College Level Evolution by AudioLearn

College-Level Evolution

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TABLE OF CONTENTS Preface........................................................................................................ 1 Chapter One: Early Evolutionary Theories .................................................. 5 Early Evolutionists ........................................................................................................... 5 Timeline of Evolutionary Theories .................................................................................. 7 Evolutionary Thought in Ancient Times ......................................................................... 8 Christian Philosophies on Evolution ............................................................................... 9 Nineteenth Century Evolution ....................................................................................... 10 After Darwin and Natural Selection .............................................................................. 12 The Story of Darwin ....................................................................................................... 13 Key Takeaways ............................................................................................................... 15 Quiz ................................................................................................................................ 16 Chapter Two: Natural Selection ................................................................ 20 What is Natural Selection? ............................................................................................ 20 Adaptation, Fitness, and Reproductive Success............................................................ 25 Studying Natural Selection ............................................................................................ 29 Natural Selection and Complex Behaviors .................................................................... 29 Key Takeaways ............................................................................................................... 31 Quiz ................................................................................................................................ 32 Chapter Three: The Study of Taxonomy and Phylogeny ............................. 36 Taxonomy....................................................................................................................... 36 Phylogenic Trees ............................................................................................................ 39 Cladistics ........................................................................................................................ 42

Phylogenetics and Molecular Phylogenetics ................................................................. 44 Key Takeaways ............................................................................................................... 46 Quiz ................................................................................................................................ 47 Chapter Four: Genetics and Genetic Variation .......................................... 51 Introduction to Genetics ................................................................................................ 51 History of Genetics ........................................................................................................ 52 Genetic Processes ........................................................................................................... 54 Mendelian Genetics ....................................................................................................... 58 Genetic Variability and Mutation .................................................................................. 60 Mutations ....................................................................................................................... 61 Key Takeaways ............................................................................................................... 62 Quiz ................................................................................................................................ 63 Chapter Five: Origin of Life ....................................................................... 67 Early Earth Environment .............................................................................................. 67 Early Forms of Life ........................................................................................................ 73 Viral Evolution ............................................................................................................... 74 Prokaryotic Cell and Eukaryotic Cell Evolution ............................................................ 75 Key Takeaways ............................................................................................................... 79 Quiz ................................................................................................................................80 Origin of Eukaryotes ...................................................................................................... 84 Evolution of Multicellularity.......................................................................................... 86 Evolution of Individuality ..............................................................................................88 Transition to Group Living ............................................................................................ 89 Key Takeaways ............................................................................................................... 91

Quiz ................................................................................................................................ 92 Chapter Seven: Species and Speciation ..................................................... 96 Identifying Species ......................................................................................................... 96 Speciation and Modes of Speciation .............................................................................. 99 Genetics of Speciation ...................................................................................................101 Key Takeaways ............................................................................................................. 102 Quiz .............................................................................................................................. 103 Chapter Eight: Evolution of the Human Species ...................................... 107 Early Man ..................................................................................................................... 107 Human Evolution......................................................................................................... 109 Human Structural Changes ..........................................................................................110 Human Migration ......................................................................................................... 112 Evidence for Human Evolution .................................................................................... 113 Evolution before the Homo Genus ............................................................................... 114 Evolution of the Homo Genus ...................................................................................... 115 Tool Usage ..................................................................................................................... 117 Behavioral Changes....................................................................................................... 117 Modern Human Evolution............................................................................................ 118 Key Takeaways .............................................................................................................. 119 Quiz .............................................................................................................................. 120 Chapter Nine: Extinction ........................................................................ 124 Extinction Basics .......................................................................................................... 124 Background Extinction ................................................................................................ 128 Mass Extinction ........................................................................................................... 129

Key Takeaways ............................................................................................................. 133 Quiz .............................................................................................................................. 134 Chapter Ten: Evolution of Reproduction ................................................. 138 Asexual Reproduction .................................................................................................. 138 Evolution of Sexual Reproduction ............................................................................... 140 Advantages and Disadvantages of Asexual Reproduction .......................................... 143 Mating Systems ............................................................................................................ 144 Sex and Mate Selection ................................................................................................ 145 Key Takeaways ............................................................................................................. 147 Quiz .............................................................................................................................. 148 Chapter Eleven: Evolution of Sociality and Populations ...........................152 Population Evolution ................................................................................................... 152 Hardy-Weinberg Model ................................................................................................155 Cooperation in Populations ......................................................................................... 156 Group Living .................................................................................................................157 Social Evolution ........................................................................................................... 158 Evolution in Finite Populations ................................................................................... 158 Key Takeaways ............................................................................................................. 160 Quiz ............................................................................................................................... 161 Chapter Twelve: Coevolution .................................................................. 165 Coevolution Explained ................................................................................................. 165 Coevolution and Mutualism ........................................................................................ 168 Host-Parasite Coevolution ........................................................................................... 169 Antagonistic Coevolution ............................................................................................. 170

Mosaic Coevolution....................................................................................................... 171 Key Takeaways ..............................................................................................................172 Quiz ...............................................................................................................................173 Chapter Thirteen: Evolution and Disease ................................................. 177 Evolution of Disease Origins ........................................................................................ 177 Disease Susceptibility .................................................................................................. 179 Host and Pathogen Evolution ...................................................................................... 180 Evolution of Senescence ............................................................................................... 181 Key Takeaways ............................................................................................................. 184 Quiz .............................................................................................................................. 185 Chapter Fourteen: Future of Evolution ................................................... 188 Holocene Extinction .................................................................................................... 188 Ways Humans Might Evolve ........................................................................................ 191 Human Extinction ....................................................................................................... 192 Future of the Planet with Global Warming ................................................................. 193 Key Takeaways ............................................................................................................. 196 Quiz .............................................................................................................................. 197 Summary ................................................................................................ 201 Course Questions and Answers ............................................................... 205

PREFACE This course has been designed to teach the interested college-level student the fundamentals of evolution. Evolution is a field of science that is continually changing as more is understood about cell biology, genetics, and the study of the early earth environment. Evolution involves the adaptation of organisms to their environment and the ways in which organisms find their niche or surpass other organisms in the process of natural selection. The course talks about the origins of life and explains what we know about how life has evolved on earth throughout the ages. As you will learn from the course, evolution is not just a historic event but is a process that continues in today s time and will continue to be part of life on earth in the future. No study of evolution would be complete without a discussion of the history of evolutionary theories, which is the topic of chapter one in the course. We will discuss some of the early evolutionists who gave rise to what we currently believe about how evolution works. We then talk in more detail about evolutionary thought throughout time, including modern evolutionary thinking. The story of Charles Darwin is a good one and will help you understand how his major breakthroughs in the understanding of evolution as a naturalist in the Nineteenth Century helped to pave the way for modern evolutionary thought. The focus of chapter two is natural selection. It is a key evolution-related process involving the ability of different organisms in a population to adapt to its environment and to pass on this adaptability to their offspring. As you will see in this chapter, natural selection relates to fitness in a given environment and an organism s reproductive success. Examples of natural selection are given as well as a discussion of how natural selection relates to complex behaviors in higher-order animals—a phenomenon known as evolutionary psychology. Chapter three in the course talks about the evolutionary relationships between the different types of living things. It starts with a discussion of taxonomy, which is the naming convention used to describe all living things. Every form of life falls under one

of three domains, Bacteria, Archaea, and Eukarya. There are other subdivisions that describe these types of arrangements. Exactly how to describe the relationships between life forms involves a discussion of phylogenetic trees. As you will see, newer findings in biology and microbiology have changed the way these phylogenetic trees are arranged. Chapter four discusses genetics and genetic variation. Genetics works on a small scale in the inheritance of certain traits by a descendant from a direct ancestor. It also works on a large scale because it is through a series of genetic mutations that new species are ultimately created. We will talk about Mendelian genetics, the science of mutations, and the advantages and disadvantages that come with certain genetic situations. Chapter five in the course introduces topics related to the origin of life on earth. Life on earth in the beginning of time was very different than it is now. This is partly due to the fact that the early conditions of earth as a planet were vastly different from that of present-day time. The chapter talks about the evolution of viruses and of prokaryotes, which were the first cells to represent life on this planet. There is more to be said about evolution than the evolution of single-celled organisms so this is the topic of chapter six. Eukaryotes are infinitely more complex than prokaryotes—even those that are unicellular. Many eukaryotic organisms are multicellular; for this reason, the evolution of multicellularity is discussed in this chapter. Because evolution happens to populations rather than to individuals, it is important to also talk about the evolution of individuality. There are advantages to evolving in a social environment, which is also covered in this chapter. The major topics of chapter seven in the course are species and speciation. Earlier chapters talk about evolution and its role in the diversity of species on earth. In this chapter, we talk about how species are defined and the different methods in which speciation or the formation of a different species occurs. Historically, species were defined by their similar characteristics but, in this chapter, we talk also about how the knowledge of genetics has changed the definition of what exactly is meant when referring to an organism being of a certain species in today s scientific terms.

Chapter eight talks about the evolution of the human species. From an evolutionary perspective, humans have not been around very long. Even so, there have been many changes that have taken place over the course of about 400,000 years. As you will see in the chapter, there have been changes in brain size and gait, among other things, that have been a part of the processes necessary to turn ancient species into modern man. The topic of chapter nine in the course is extinction, which is the final termination of a specific organism type or species. This has occurred to 99 percent of all species that have ever lived on earth. We will talk about background extinction, which happens over a period of time for a variety of reasons, as well as extinction events that have occurred in the earth s history, leading to the mass extinction of many of the species on earth at roughly the same time. Chapter ten discusses issues related to the evolution of reproduction. There are basically two broad categories of reproduction, which are asexual reproduction and sexual reproduction. There are evolutionary advantages and disadvantages of both that will be compared in this chapter. With sexual reproduction, in particular, there are complex variables involved in mate selection, which will also be covered along with the evolutionary issues related to human sexuality and human sexual reproduction. The focuses of chapter eleven in the course are evolution within populations and the evolution of social behaviors. Anytime there is a group of individuals in a population, there will be issues of conflict and cooperation, which are discussed in the chapter. Social behaviors are complex but have genetic and evolutionary influences. Topics also included in the chapter are the Hardy-Weinberg Principle and the evolution involved in finite populations. Chapter twelve focuses on the subject of coevolution. Coevolution is a phenomenon that happens when two or more species affect each other s evolutionary processes. This can happen when two species have a mutualistic relationship or when there is a hostparasite relationship. There are two other types of coevolution discussed in this chapter, including antagonistic coevolution and mosaic coevolution, which involve specialized relationships between two or more species.

The focus of chapter thirteen in the course is evolution and disease. Diseases affecting all species have been around since the beginning of time. The way in which diseases have originated is discussed in this chapter, including how some human diseases have crossed species to affect humans. Also covered in the chapter is the evolution of senescence or aging. There are several theories as to how and why humans age, which are discussed in the chapter.

Chapter fourteen looks at the future of evolution, particularly of humans and of the planet itself. We will talk about what s already happened with the Holocene extinction, often called the sixth mass extinction event on earth. Exactly how humans will evolve is unknown but scientists can make some speculations, which are discussed in the chapter. Human extinction is covered as a possibility as is the future of the planet with the progress of global warming, which will affect the earth itself and the humans on it.

CHAPTER ONE: EARLY EVOLUTIONARY THEORIES No study of evolution would be complete without a discussion of the history of evolutionary theories, which is the topic of this chapter. We will discuss some of the early evolutionists who gave rise to what we currently believe about how evolution works. We then talk in more detail about evolutionary thought throughout time, including modern evolutionary thinking. The story of Charles Darwin is a good one and will help you understand how his major breakthroughs in the understanding of evolution as a naturalist in the Nineteenth Century helped to pave the way for modern evolutionary thought.

EARLY EVOLUTIONISTS The study of evolution did not miraculously begin with Charles Darwin. There have been ideas about evolution since the time of Ancient Greece. About 2600 years ago, in an area of the world now known as Turkey, Anaximander studied geology and astronomy. He came to understand that earth was a solitary entity that didn t actually rest on anything. He believed that early life began in a wet rather than a dry environment, that life gradually evolved into a drier environment, and that mankind did not exist on earth in their current form from the beginning. He believed that human ancestors were once fish and based his reasoning on the idea that, because human babies cannot look after themselves, there must have been an ancestor that could do this. Empedocles lived from about 490 BCE to 430 BCE. He was a scientist and Ancient Greek philosopher. He believed that everything was made from a combination of earth, water, fire, and air. He came up with the first ideas about natural selection but did not go as far as saying that natural selection led to different species. He thought that early earth was filled with monstrous creatures that had been selected out over time and had since become extinct so that more adaptable forms of life existed in modern times. The era of the Ancient Greeks set many of the ideas on evolution for many centuries. Carl Linnaeus was a natural scientist in the 1700s. He was the first to develop the scientific forms of we now understand as the genus and species names of living things. Homo sapiens is the scientific designation for humans; every other species on earth has a similar scientific name that defines it. He believed that God started all life on an island with just a few beginning species.

In 1753, Comte de Buffon studied evolution and believed that all four-legged creatures were developed from a single common ancestor. He believed that four-legged animals were the perfect species above that of other animals. James Hutton was actually a geologist in the late 1700s. He furthered the ideas of natural selection, believing that, if an organism was not suitable or adapted in an environment so that it could not procreate, it was selected out so that forms of life that were more likely to procreate replaced it. Erasmus Darwin was the grandfather of Charles Darwin. He studied reproduction but believed that it was a filament that fathers contributed to the making of an embryo but that the mother did not contribute to any part of the embryo. Instead, the mother was the home to the embryo and provided it with the nutrients and oxygen necessary for growth. He believed that warmblooded animals came from some common ancestor. He believed that all plants and animals had a common ancestor. He felt that competition between males led to the survival of the fittest. Jean-Baptiste Lamarck developed a theory in 1800 that an animal could pass on certain traits to their offspring if they used the trait more often. As an example, if a man worked out and was muscular, his children would be born more muscular. While this was wrong, he did also believe that evolution was both slow and gradual. This is only partially true because it doesn t account for sudden mutations in an organism or its offspring. William Wells stated in 1813 that, when breeding animals, people could select out certain traits and breed animals with those traits, leading to the different domesticated animals. He furthered his theory to people but not to other species. This was basically an idea in support of natural selection. Geoffroy Saint-Hilaire was a researcher in the 1800s. He believed in evolution that could occur in large steps because of influences in the environment. He also believed that new species could arise in this fashion. Finally, he proposed the idea that birds evolved from reptiles, long before this was shown to be true archaeologically. Two contemporaries of Charles Darwin rejected Lamarckism, which was blatantly wrong, and felt that all forms of life could become other species. These were Robert Grant and Charles Lyell. They felt there was a common origin for modern plants and animals but did not understand how species transformation could take place. Edward Blyth was alive in the early 1800s. He understood about artificial selection, which is selection used by breeders of domestic animals. He also knew that there were variations within

a species. He furthered his ideas by indicating that the variations in a species could be acted on in the natural environment through natural selection but didn t believe that new species could come from this. Instead, he believed that natural selection kept a species in its truest form. Robert Chambers published a book anonymously in 1844 that greatly opposed the religious views of his era. He wrote that the solar system developed from a nebula and that life sprung up on earth spontaneously. He didn t understand how evolution actually happened. The book was believed to have prepared the public for the work of Charles Darwin. Charles Darwin and Alfred Wallace wrote a joint paper in 1858 on evolution through natural selection. In 1959, The Origin of Species was published that showed evidence of natural selection. It left essentially no question in the minds of scientists that natural selection existed. This did not make it instantly popular, however. It was not fully accepted until the 1930s by most scientists.

TIMELINE OF EVOLUTIONARY THEORIES In this section, we will talk more about the timeline of evolutionary thought. There have been ideas related to evolution in the ancient cultures of the Romans, Greeks, Chinese, and Islam. There were two opposing thoughts that were discussed as part of the evolutionary debate. The first was essentialism”, which argued that every species on earth has unalterable characteristics. This was in line with the theology of the time. The second was evolutionary cosmology along with naturalism, which was the idea that the different species characteristics were variable. We ve already talked about early evolutionary thought; however, evolutionary thinking has changed in recent years with the knowledge about genetics and biology contributing to modern synthesis. This looks at genetic diversity in species populations and applies the study of paleontology and comparative anatomy to determine how the different species have evolved over time. Most recently, DNA sequencing has led to an understanding of phylogenetics from a molecular perspective. We will talk about the current three-domain system of all life, that was developed by Carl Woese, later in this course. For now, you should know that this is a relatively recent phenomenon in evolutionary thinking.

EVOLUTIONARY THOUGHT IN ANCIENT TIMES Anaximander of Miletus lived from about 610 BCE to 546 BCE. He was a pre-Socratic philosopher. As mentioned, he believed that life originated in water, with creatures eventually spending more time on land than in the water over time. He believed that man must have been first the child of another type of animal, probably some type of fish, because modern man could not have survived early life on earth if he needed to be cared for as long as humans do before maturity. Philosophers at the time subscribed to essentialism, which was the belief in the unchanging essences of every living thing. In evolutionary thought, it involved the idea that species characteristics did not change over time but were fixed entities. Empedocles said that the birth and death experience simple mingled and separated the different elements that make up an organism. He believed that current animals and plants were derived from pieces and parts of older organisms that were mingled inside the embryo. Empedocles relative contemporaries did not believe this. In fact, Plato and Aristotle said that all things were fixed through divine design. Plato believed in essentialism and some type of creator of all things. He did not believe that species could transform. Aristotle believed in a great ladder of life” or chain of being” that was static over time. He believed that the final form of an organism perfectly served their function. He rejected Empedocles work. Zeno, about a century later, founded the Stoic school of philosophy and agreed with Aristotle. He believed in teleology, in which all features of nature showed evidence of having a purposeful design. The Roman Empire followed most of the Ancient Greek philosophers when it comes to timeline. Lucretius was one of the Romans who wrote on the development of the earth, humans, and other living things. His approach was purely naturalistic and did not reference any type of supernatural involvement. This work led to the beliefs that came during the Renaissance. Other theorists of the Roman era belonged to the Stoic school of thought. This included Seneca the Younger, Cicero, and Pliny the Elder. These philosophers influenced Christian thoughts on evolution because their thoughts were largely teleological and based on the theological origin of the different species. Origen of Alexandria was a third-century church father and Christian philosopher. While he supported the creationist beliefs in the Book of Genesis, he said it was all allegorical and should

not be interpreted literally. He did not believe that people should truly expect that the universe was entirely made in seven days. After Origen of Alexandria, there was Augustine of Hippo, who also believed that the creationist story should not be accepted as literal fact. He felt that some creatures were derived from the decomposition of early life forms. It was stated in his book On the Literal Meaning of Genesis that living things were not perfect but had the potential to be so. He also believed that life gradually transformed over time. In later times, the Roman Empire fell and Islamic philosophers predominated in the 8th through 13th centuries. Al Jahiz said that stronger animals devoured weaker animals in a struggle for existence and that God disposed some creatures in favor of others. He also wrote about the food chain in living things.

CHRISTIAN PHILOSOPHIES ON EVOLUTION The time of the Middle Ages was when much of Ancient Greek teachings were lost to Westerners. These had, however, been preserved in the Islamic cultures and were translated into Latin by the twelfth century. There were Christian thinkers, such as Peter Abelard and Thomas Aquinas, who looked at Aristotle s and Plato s work about the goodness of God, believing in the perfection of all things and in the great chain of being, which looked at the organization of all living things, inanimate objects, and spiritual beings. According to the great chain of being, there was an order of things, ranging from lowest to highest. Hell existed at the bottom of the chain and God was listed at the top. Mankind was in the middle, while worms were thought to be the lowest form of animal life. No species could transform into another or change places in the linkages that made up the great chain of being. The Book of Genesis was revered and it was believed that the hierarchy involved in the great chain of being was unchangeable. Thomas Aquinas was a Christian theologian who also believed that the Book of Genesis shouldn t be interpreted literally because it conflicted with the way that natural philosophers had learned already about how nature works. He said that God basically set up nature to run on its own natural processes, believing there was no conflict between theology and the development of the universe through natural mechanisms. He did not believe Empedocles, who said that there was no purpose in how things have evolved. He believed that nature was a form of divine art.

In the early 1600s, Rene Descartes developed mechanical philosophy, in which the universe was a sort of natural machine. There were others that followed him and indicated that all of the universe had developed without divine intervention. This was different from philosophers like Gottfried Leibniz and Johann Herder, who believed that evolution was a divine process. Pierre Maupertuis had a materialistic view of nature, indicating that reproduction created natural modifications that accrued over many generations to produce new species and new races of man. He was in support of natural selection and opposed taxonomists who felt that the qualities of species were unchanging. This idea of unchanging species was characteristic of natural theological thinking. In the late 1700s, theorists like James Burnett said that man probably developed from primates and that species evolved over time due to their overall responses to the environment. As mentioned, Erasmus Darwin was a part of this but said that a single living filament gave rise to all warm-blooded animals.

NINETEENTH CENTURY EVOLUTION The ideas and findings of paleontologists entered into evolutionary thinking by the early 19th century. George Cuvier looked at the structural differences between elephants of today, mastodons, and mammoths, which are extinct. He said they were distinct species and was the first to describe the probability that a species could become extinct. Fossils were increasingly looked at in rock layers, which helped to establish how old the earth was. Cuvier said that catastrophism in nature explained some extinction patterns. He also looked at fossil records to see how plant life has evolved. John Phillips, in 1841, identified three major eras in geology. These were the Paleozoic era, which involved the predominance of marine invertebrates, the Mesozoic era, which was predominated by reptiles, and the Cenozoic era, which was dominated by mammals. There was also the work of Adam Sedgwick and William Buckland, who also believed that catastrophic events led to mass extinction and the arrival of new species. Unlike more progressive theorists, researchers like William Buckland believed that the biblical flood was the last major catastrophe in terms of evolution and extinction. Charles Lyell, on the other hand, said that there were more gradual changes in geology that contributed to evolution rather than cataclysmic events.

Jean-Baptiste Lamarck studied the transmutation of species. He did not think there was a common ancestor but that there were simple forms of life that were still being spontaneously generated. He felt that there was some type of life force that caused species to be more complex with time. This was related to the great chain of being. Remember too that he thought that changes in a species adaptation to the environment during its lifetime were later inherited by the offspring. The concept of transmutation of species was a more primitive explanation for evolution. It described the ways in which certain species transformed into other species. Certain idealists like Louis Agassiz and Richard Own believed that species of plants and animals had fixed characteristics that were both unchangeable and developed by the creator. They used embryological patterns of development could explain the relationships between the species. Each of these ideas made Charles Darwin more convinced that he needed proof and sound science to back his theories. As you have learned too, there were many ideas that predated Charles Darwin s theories on natural selection. Darwin himself looked at selective breeding and the ideas put forth by others indicating that harsh environmental conditions led to weeding out of the weakest individuals in a population. When Darwin wrote on natural selection, he named those early theorists that had anticipated natural selection before it was somewhat more proven. Also prior to Darwin was Patrick Matthew, who indicated that, if there was enough of an evolutionary change leading to a new species, the new species might not be able to reproduce with species it had evolved from. This is how he defined a new species. We will talk about Charles Darwin in a minute but suffice it to say, he did not believe in the fixity of species, writing secretly on the transmutation of species prior to his actual finished work on natural selection. By the time of Darwin in the 1850s, it was a hot topic of debate as to whether or not species evolved. Darwin s work changed all that by indicating that evolution existed by new species diverging from existing species. Thomas Henry Huxley was an anatomist who was convinced by Darwin s work on the origin of species. He displaced the ideas of natural theology with naturalism, which did not involve theological ideas. Huxley used paleontology to help explain aspects of evolution, which included the idea that birds evolved from reptiles. This was proven by the discovery of Archaeopteryx in Europe as well as North American ancient birds that had teeth. The evolution of horses was also uncovered through paleontological records.

AFTER DARWIN AND NATURAL SELECTION Darwin largely ignored issues related to human evolution in his work because of the controversies associated with the idea that humans evolved from lower animals. It was first believed that humans existed on earth for just a few thousand years. Then, there were archaeological digs that stretched for many thousands of years, indicating that human ancestors existed for thousands of years before that. Java man was discovered in the 1890s, which served as a bridge between Neanderthals and modern man. Thomas Henry Huxley wrote about the similarities between gorillas and humans, including similarities in brain structure. He wrote a book on the subject in 1863. Lyell and Wallace felt that there were similarities between apes and humans but felt that there was a common ancestor for each of the species of primates, including humans. Darwin later wrote that the differences between primate thinking and human thinking were a matter of degree rather than substance. There were four major alternatives to the idea of natural selection that were espoused in the latter part of the 19th century. There was theistic evolution, orthogenesis, neo-Lamarckism, and saltationism. These are explained as follows: •

Theistic evolution—this basically tries to align science with modern religious beliefs and isn’t really a scientific theory at all.

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Neo-Lamarckism—this is the idea that use or disuse of a body structure allows it to be passed on or not passed on to the offspring.

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Orthogenesis—this involves the idea that there is a driving force that allows for evolution to go in a specific direction.

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Saltationism—this is the idea that a single mutation has the potential to change offspring into an entirely new species all in one step.

We will discuss Mendelian genetics in a few chapters. He discovered the laws of inheritance that became more popular around 1900. At the time, there were the Mendelians, who looked at variations in a species as they apply to the laws of inheritance. There were also the biometricians, who were more interested in the variation of specific characteristics within populations of organisms. These two camps opposed each other. The two camps came together with the study of population genetics, which argued that larger changes in a population could come about by the natural selection and change in the frequencies

of a large number of genes in a population. This was believed to be how new species could be developed. We will talk about the evolution of moths in populations where being a certain color offered better protection against predators. This indicated that natural selection could actually happen quite quickly. Modern synthesis of evolutionary thought came about in the twentieth century. This combined natural selection, genetic variation, and Mendelian inheritance into modern evolutionary thinking. There was a shift away from pure natural selection to ideas related to genetic drift within a population. A species came to be defined as a population of organisms that could breed together and that were reproductively different and isolated from others in the population. In the middle of the twentieth century, there was a rise in molecular biology and the discovery of DNA and genetic codes. Biochemists Emile Zuckerkandl and Linus Pauling developed the molecular clock theory, which was that sequence differences between related proteins in different species could help define how far apart they were in terms of species divergence. By the late twentieth century, there came to be a more gene-centered view of evolution. It was believed that sexual reproduction helped to create better resistance among the offspring to parasites and other pathogenic organisms. Sexual reproduction creates genetic diversity, which is felt to be better for the species overall. Whether or not sexual reproduction is truly better for a species or not is still the subject of debate. Most of evolutionary thought was developed without the background of microbiology. Because of advances in the study of the genes in microbes, called microbial genomics, small microorganisms can be studied as to the differences in the species. Horizontal gene transfer was identified in 1959, which is the way that pieces of genetic material can be transferred between different bacterial species, which in many cases, leads to antibiotic resistance. This phenomenon is believed to play a role in creating new species of microorganisms.

THE STORY OF DARWIN As you have seen, Charles Darwin did not develop his theories on evolution and the origin of species in a vacuum. His weren t the first words on evolution in the world and they haven t been the last words on the subject. Even so, he did a remarkable job of studying certain populations and wrote a landmark book On the Origin of Species. Darwin gained a reputation as an important fossil collector and geologist. He studied naturalism rather than become a clergyman. He became convinced in the idea of the

transmutation of species after learning about bird specimens gathered from the Galapagos Islands. He also studied orangutans in the zoo as to their facial expressions; he studied animal breeding and how that changed the fitness of subsequent litters of domesticated animals. He initially studied under Robert Edmund Grant and learned of Lamarck s ideas and the work of his grandfather Erasmus Darwin, showing a common ancestor to modern animals and plants. He collected beetles and took his voyage to other parts of the world on a ship called the Beagle. He did not develop his evolutionary ideas because of his work on the Beagle, however. While on the Beagle, he collected numerous fossils and zoological specimens. Afterward, he looked around for zoologists to help him catalog his specimens. It was actually ornithologist John Gould who took on the bird specimens Darwin had collected; it was Gould who recognized that the birds collected were actually about 12 different species of finches. Darwin was extremely concerned that his work met the accepted scientific methodology of the day. He did not want to simply present theories; he wanted facts to back them. There were many who believed in theistic evolution at the time and, while he was a religious man, he wanted to be very scientific about his findings. He came to understand that, while individual organisms did not change over time, their offspring could change because of the reproductive process. Those offspring that adapted better could bring forth offspring that also fared better when it came to adaptation. He felt that geographic isolation led to reproductive isolation of species that lived there. This would lead to divergence of species and to what he called geographic speciation. It was exactly these circumstances that existed on the Galapagos Islands. Darwin actually wrote about a number of things besides the origin of species. He wrote about barnacles, geological topics including earthquakes, and orangutans in the zoo. He was ill throughout most of his adult life but still kept a busy working life, ultimately writing his seminal work on the origin of species more than 20 years after his voyage on the Beagle.

KEY TAKEAWAYS •

There have been ideas in support of evolutionary theory since the ancient times, first proposed by pre-Socratic scholars.

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Almost all of the early theories on evolution were made without the knowledge we currently have about microbiology and genetics.

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Natural selection involves the adaptation of an organism to its environment and the ability to pass on these adaptations to one’s offspring.

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Charles Darwin was not the first nor the last to talk about the origin of species and speciation but he spent a great deal of time studying the phenomenon in the wilds of the Galapagos Islands.

QUIZ 1. What did Anaximander believe that humans ultimately evolved from? a. Plasma b. Fish c. Trees d. Plant forms Answer: b. Anaximander thought that humans evolved from some type of ancient fish. He felt that life began in a wet environment and evolved into living on a drier environment. 2. What area of evolution was the focus of Empedocles in Ancient Greece? a. The evolution of man from apes. b. The theory that animals and plants evolved separately. c. The theory of natural selection to cause monstrous forms of life to become extinct. d. The evolution of the different species over time. Answer: c. Empedocles developed a theory that life was once filled with monstrous creatures that were selected out through natural selection but didn t understand that different species came out of the process. 3. What theorist in evolutionary theory was perhaps the most wrong in his theories? a. Lamarck b. William Wells c. Saint-Hilaire d. Robert Grant Answer: a. Lamarck developed Lamarckism, which was the idea that, if certain body parts were used most often in an organism s life, these were preferentially passed on to the environment.

4. What can best be described as artificial selection? a. The idea that using a certain body part more could mean it gets passed down to the offspring. b. The process of selection that occurs in the breeding of domestic animals. c. The process of selection that occurs in a finite population. d. The process where certain species become extinct so others could take their niche. Answer: b. The process of selection that occurs in the breeding of domestic animals is referred to as artificial selection. 5. The idea that all of a species’ characteristics are unchanging over time is called what? a. Essentialism b. Rational thought c. Natural selection d. Naturalism Answer: a. Essentialism has many different manifestations, depending on the field of study. In evolution, this is the idea that all species have characteristics that are unchanging over time. 6. Which ancient philosopher least believed in theology and the divine nature of things? a. Plato b. Aristotle c. Empedocles d. Zeno Answer: c. Each of these philosophers believed that there was divine design for how things are made and that every organism is made specifically so they are suited to their environment.

7. What was not a major contribution to science by George Cuvier? a. The description that elephants, mastodons, and mammoths were different species. b. The idea that species could become extinct. c. The concept that plants evolved into animal species. d. The idea that catastrophism led to certain types of extinction. Answer: c. Each of these was a contribution to science and especially the science of evolution that came out of George Cuvier s work. He looked at the evolution of plant life but did not suggest that animals came from plant life. 8. What is the dominant life form in the Cenozoic era as defined by John Phillips? a. Reptiles b. Invertebrates c. Plant life d. Mammals Answer: d. In the Cenozoic era, the dominant organism has been mammals. This is different from the Paleozoic era and the Mesozoic era, which were dominated by marine invertebrates and reptiles, respectively. 9. The idea that a single mutation has the potential to alter offspring to such a degree that a new species can arise in a single step is called what? a. Theistic evolution b. Neo-Lamarckism c. Orthogenesis d. Saltationism Answer: d. In saltationism, the idea is that a single mutation has the potential to change offspring so they are of a different species than the parent.

10. According to the molecular clock hypothesis, what could help tell the time period between when two species diverged? a. Their DNA genome b. Differences in related protein sequences c. Anatomic measurements between the species d. Differences in their archaeological patterns Answer: b. Differences in protein sequences in related proteins in different species could tell the time when the species diverged from each other, according to the molecular clock hypothesis.

CHAPTER TWO: NATURAL SELECTION The focus of this chapter is natural selection. It is a key evolution-related process involving the ability of different organisms in a population to adapt to its environment and to pass on this adaptability to their offspring. As you will see in this chapter, natural selection relates to fitness in a given environment and an organism s reproductive success. Examples of natural selection are given as well as how natural selection relates to complex behaviors in higher-order animals— a phenomenon known as evolutionary psychology.

WHAT IS NATURAL SELECTION? Natural selection involves the differences in adaptation and survival in an environment, coupled with reproductive success or failure, depending on the environment and on which species live well or live poorly in niche they live in. It depends on competition for resources so that not all members of a group have 100 percent access to resources. Natural section is different from artificial selection. Artificial selection is intentional and is what happens when breeders of domesticated animals select out certain offspring who are considered more perfect”. The best offspring are bred again so that, over time, the species changes and offspring are more likely to have the desirable characteristics. There are natural variations in all groups of organisms. Some comes from random genetic mutations in the genomes of the individual organisms, which are inherited. The genotype is the actual collection of genes in a particular organism, while the phenotype is what you see in an organism because of its genotype. It s the phenotype that interacts with the environment to give an organism an advantage or disadvantage to the organism. What is the environment of the organism? It is not just the abiotic (nonliving) factors. It also involves the molecular biological circumstances of the cell, other cells near the organism and the entire population the organism lives in. The goal of every organism is to adapt or survive in their environment and to reproduce within it. the reproductive success depends on sexual selection, which is the selection of a mate, and what s called fecundity selection, which is the selection of traits that make an organism better able to reproduce. Large female size in certain insects confers fecundity selection to that organism.

Due to differences in the phenotype of the organisms that get passed down to offspring, an organism can develop its own special ecological niche, which is the area they do better at in terms of adaptation than other organisms. This development of an ecological niche is called microevolution”. If large changes occur in an organism, speciation can occur, which is the emergence of a new species. This is referred to as macroevolution. Natural selection is the main reason why organisms exhibit what s referred to as adaptive evolution”. Charles Darwin himself defined natural selection as a way to lead to speciation. He believed that individual traits, if they are positively linked to adaptation, will be preserved for reproduction and the furthering of the trait and the species. Those animals or plants that had traits which enhanced survival would be more likely to reproduce. This leads to progressive evolution of certain populations within a species. If this is extreme, new species will develop. Part of natural selection is the idea of competition for resources. According to Thomas Robert Malthus, a political economist who worked with Darwin, an unchecked population will increase in number exponentially, while the food supply only grows arithmetically. This leads to limited resources and competition. Darwin developed his theory somewhat before he developed evidence for it. He and others wrote a paper on the tendency of all species to form varieties within the population. While he studied finches in the Galapagos, he also studied pigeons, which had different variations and different species because of selective breeding or artificial selection. Back in Darwin s day, natural selection explained all of evolution. While it was controversial because it was felt to be too weak of an influence on speciation, it was also controversial because it was not guided by anything. It was Herbert Spencer who coined the phrase survival of the fittest” after reading Darwin s works. Modern biologists do not use this term, however, because it means that the fittest organisms are somehow functionally superior, which is not always the case. The idea of natural selection was developed before genetics itself was discovered in 1900. After putting together Mendel s laws of inheritance through genes and Darwin s natural selection, the concept of natural selection became more accepted by mainstream scientists, who reformed all the concepts into what was called modern synthesis. Out of this came the idea that certain patterns of gene activity determined the phenotype of the organism. An important factor in creating new species is the idea of reproductive isolation. Animals that thrive together on an island or islands like the Galapagos Archipelago create reproductive

isolation because there is no mating with larger numbers of organisms. This supports the formation of new species. By the end of the twentieth century, there was a sort of second modern synthetic thought, which brought in what is now known about molecular genetics. This created the field of evolutionary developmental biology, referred to as evo-devo”. This field looks at what we know about the evolution of embryonic development in order to explain the relationships between different species. Think about the fact that human embryos have limb paddles and tails in utero that are lost in embryonic development. This is what is studied in evolutionary developmental biology. In reality, natural selection is not completely based on heritability of traits. Some traits that affect an organism aren t fully heritable. Natural selection is blind to heritability but not blind to phenotype. Traits that tend to lead to better reproductive success in an organism are said to be selected for”, while traits that lessen reproductive success are said to be selected against”. There was an interesting phenomenon that took place during the industrial revolution that was a direct result of a rather rapid form of natural selection. Excessive pollution killed off the lichens that otherwise lightened the tree trunks. This left behind dark tree trunks. There were both light-colored and dark-colored peppered moths. The dark peppered moths were less likely to be eaten by birds compared to the light peppered moths. This selected for dark coloration so there was an increase in dark colored moths in the population. When the Clean Air Act of 1956 caused lichen to return to the area, light colored moths again were predominant. Natural selection is based on the idea that there will be genetic variation in every population. Some of the variations will enhance survival and reproductive success, while other variations do exactly the opposite. There will only be differential reproduction if the varied trait is heritable. Slight variations may take many generations to have an effect. It is the environment the organism lives in that selects for or against a specific trait. This is not intentional but it is not completely random either. Artificial selection is, on the other hand, largely intentional. Fitness is important to the study of natural selection. More fit” organisms survive better and longer so they can reproduce. Fitness does not relate as much to the longevity of an organism as it does to the reproductive success of the organism. More offspring means a greater ability to have more of the organism s successful genes in the environment. There is a difference between survival of the fittest” and improvement in fitness”. Survival of the fittest only removes those that are not as fit but doesn t necessarily create fitter organisms overall. Improvement can only come through mutations that turn out to be beneficial to the organisms who have it.

Competition is also important. It leads to greater fitness in one organism and lesser fitness in another organism and depends on a limited supply of resources, which can be territory, food, or water. Competition can happen between different species or among the same species. It isn t as important in places where animals have room to roam and find new resources. With directional selection in an environment, a single extreme phenotype is favored over others. With stabilizing selection, an intermediate phenotype is favored over extreme phenotypes. In disruptive selection two separate extremes, usually occupying different niches, are favored over an intermediate phenotype between the two extremes. Disruptive selection can become a precursor to actual speciation. Natural selection can be classified by the life cycle stage of an organism at which the selection acts. Viability selection is also called survival selection. It asks to increase the probability of an organism s survival in the first place. Fecundity selection, which is also called reproductive selection or fertility selection increases an organism s ability to reproduce. Fecundity survival can be divided into gametic selection, which increases the survival of the gamete, and compatibility selection, which increases the formation of a zygote or fertilized gamete. Sexual selection involved competition between organisms so they will be more likely to be selected as a mate. The plumage on a male peacock is an example of how sexual selection works. Sometimes this form of selection is done while creating risk to the organism s viability. Ecological selection is any other type of selection in a population, such as infanticide, competition, and kin selection. After Darwin, sexual selection was separated out from other types of ecological selection. Sexual selection can be intrasexual, meaning that it is competition between members of the same sex, such as is seen in male-male competition. It can also be intersexual competition, which involves how one gender selects a specific mate of the other gender. In most species, it is the females who do the choosing of the male mate, although this is not universal. The extravagant male plumage will cause a positive feedback loop, resulting in sexual desire. The antlers in stags of some animals are part of intrasexual competition. Among microorganisms like bacteria, natural selection takes place in the development of resistance to antibiotics. Antibiotics like penicillin used to be very effective in killing certain bacteria. This is now not the case, since methicillin-resistant Staphylococcus aureus or MRSA has become prominent. Because of the presence of these organisms, different antibiotics are used to kill them. Unfortunately, this only leads to multi-drug resistant organisms. This has led to a sort of evolutionary arms race, in which researchers must come up with stronger and

different antibiotics to kill the organism. The same thing has happened with insects and pesticides. In order for natural selection to lead to speciation, the differences in organism traits must be heritable. Mutations in certain genes must happen to change the genes or actual chromosomes within the organism s cells. A change in genetics can be advantageous or disadvantageous. Most genetic changes are seen in DNA that does not code for a protein and is therefore a neutral mutation. Most mutations are harmful. The biggest changes happen in regulatory genes that affect many other genes. Most of the time, these too are lethal to the cell. If the environment changes, what becomes advantageous can instead be deleterious to the organism. As mentioned, true speciation requires reproductive isolation or a reduction in gene flow. Hybrids are generally selected against rather than selected for the organism. Ultimately, a species is differentiated from others by its ability to procreate within its own species rather than with another. When a certain allele in a gene leads to greater fitness of the organism, this leads to more of the allele being in a population. This continues onward until the allele becomes fixed so that the whole population carries the phenotype or physical characteristics that can be gotten by the fitter allele. This is called directional selection. The opposite happens if the allele is bad for the phenotype s fitness. Eventually, the allele disappears. This is called stabilizing selection. Purifying selection helps to hang onto certain genetic features by exerting selective pressure that knocks out bad or harmful variants. In some cases, being a heterozygote with regard to a certain trait, which involves having two different alleles of the same gene, is better than being a homozygote, leading to a normal organism or an organism with two of the identified alleles. This is the case with sickle-cell trait in mankind. The normal person is at increased risk for malaria and being homozygous for sickle cell anemia is also bad. Heterozygotes for the trait have the advantage. There is a phenomenon of genetic hitchhiking. This happens when to genes are so close together that when recombination occurs in the making of gametes or sex cells, they are often combined together. If one of the genes is selected for in a population, so is the other, even if it is a neutral gene or is slightly deleterious to the organism. This is sometimes how genes and their closeness are measured. Selective sweeps happen because of positive selection, while background selection causes a gene to be weeded out because of purifying or negative selection.

ADAPTATION, FITNESS, AND REPRODUCTIVE SUCCESS In biological systems, adaptation has three different meanings. First, it is the process that helps an organism fit into their environment so that it is evolutionarily fit. Second, it is a state that is reached by a specific population as part of the fitness process. Third, it is any phenotypic trait that is maintained because it has evolved through natural selection. Darwin believed that adaptation was a big part of natural selection. Adaptation is directly related to the biological fitness of an organism. Gene frequencies in a population help to determine who adapts and who does not adapt. Sometimes, adaptation happens because more than one species coevolves in order to become entwined with one another in the evolutionary process. Teleology refers to the structure and purpose of the different body features of an organism, which contributes to their adaptation. While adaptation relates to teleology, it is not the same thing. Adaptation is an actual process that happens because of the form and function of a body part. There are many parts of a plant or animal that can be called adaptations, which are things that increase the fitness of the organism in its environment. The diversity of organisms in the environment is dependent on two different things: speciation and adaptation. Adaptation does not lead to reproductive isolation but speciation does. Adaptation is not simply having the ideal phenotype for a given environment. For example, an organism must remain viable at all of its different stages of development and must be viable as evolution progresses. Each genetic change and each phenotypic change in the different generations must be small because environments and the relationship between the organism and the environment are very complex. Even so, some adaptations have been very big, such as when eukaryotes were first developed in the evolutionary process by engulfing certain prokaryotes that led to the development of chloroplasts and mitochondria. Adaptations help an organism survive in its particular niche. Adaptations can be physiological, structural, or behavioral. Structural adaptations can be seen, while physiological adaptations cannot be seen but are determined through biochemistry or microbiology. Behavioral adaptations are inherited behaviors, like instincts or the capacity to learn. Mating patterns, the ability to find food, and vocalizations are behavioral adaptations, while making slime, phototropism, and the making of venom are physiological adaptations. Other physiological adaptations involve the ability to regulate temperature and things that affect growth and development.

Adaptation is not the same as acclimatization, learning, and flexibility, which happen in life and are not inherited. Flexibility involves the capacity to live in different habitats. Acclimatization involves making physiological adjustments to the environment. Learning involves improving behavior performance and is not inherited. The degree of flexibility of an organism is inherited but not flexibility itself. Certain herbivores like giant pandas and koalas are not very flexible because they can only live on certain types of food. Generalists can survive in many different types of conditions. These include most carnivores, crabs, rats, and humans. Humans can adapt to different altitudes by making more red blood cells. This is called acclimatization, which isn t heritable. Like flexibility, the ability to acclimatize is heritable, however. As climates change in the world, so does the habitat. As the habitat is changed, so do the biota. The numbers of different species in a habitat always change. When the habitat changes, there can be a genetic change in the organism, there can be habitat tracking, and there can be extinction of the species. Only genetic change leads to adaptation. Habitat tracking basically leads to the movement of the organism from one place to a better habitat. Genetic change involves natural selection that leads to certain organisms being better suited to the habitat. The genetic change can be structural or physiological. Adaptation is a process that never ends. Ultimately, though, there can be an equilibrium so that the species best fits its environment. If the habitat changes too rapidly, genetic change does not occur fast enough. This can lead to the bringing back of a population from near-extinction if they move or if enough genetic change has occurred. This is called evolutionary rescue. If it does not happen, extinction will occur. Co-adaptation happens when two species are dependent upon one another. One species will adapt to changes in the environment and the other species co-adapts accordingly. This is basically what happened in the evolution of flowering plants and the insects that pollinate the plants. Mimicry happens in some species as part of adaptation. There is a type of mimicry called Batesian mimicry, which was discovered by Henry Walter Bates, who studied mimicry in certain insects. This happens when insects that are palatable evolve to mimic those that are unpalatable so they don t get eaten by predators. This provides further evidence for natural selection. There are downsides to every adaptation. Adaptations in one area can lead to maladaptation in another area, such as the development of feathers for penguins, who do not fly at all. Some

adaptations can be just as destructive as they are helpful. This highlights the imperfection of nature in creating adaptations for different species. Most adaptations are a compromise. An example of this is the camouflage in some animals that must be broken in order to display brighter colors during the mating season. Even in humans, adaptation is a compromise. The human brain and hence, the human skull, is small and immature at birth by necessity. If the brain was larger and more mature, the infant could not fit through the birth canal and would not survive birth. This is known as birth compromise. The tradeoff is that human pelvises must be created for bipedal locomotion, which is considered a positive adaptation in humans. Pre-adaptation happens when a population is well-adapted to the environment without having prior experience with the habitat. It can happen because a species already has a lot of genetic variability. This is true of microorganisms, that have such large populations that at least some of them will survive a given habitat. Exaptation involves having a certain trait as an adaptation for another purpose that helps still another aspect of adaptation. Feathers, for example, on an ancient dinosaur were created for insulation but they have the added ability, called an exaptation, to fly. There are also non-adaptive traits that have either a neutral or bad effect on the organism s fitness for a specific habitat. These traits are called spandrels, which are adaptations that have no specific function. Other traits may have been once adaptive but have later become either maladapted or completely unnecessary. These are called vestigial adaptations. Many organisms in nature, including humans, have vestigial organs. Wisdom teeth, for example are vestigial. Extinction happens when an organism cannot keep up with the change in habitat. It happens when the death rate exceeds the birth rate for an extended period of time. Ultimately, the species disappears. Coextinction can also occur if one species becomes extinct and another dependent organism also becomes extinct. It can happen when the food chain becomes disrupted or when a flowering plant loses the insect that normally pollinates it. Fitness is what represents the combination of natural and sexual selection. A genotype or phenotype can exhibit fitness. Either of these ultimately relates to the reproductive success of the organism. Fitness can be described as the average contribution an organism makes to the gene pool of the subsequent generation. If an organism is asexual, its genotype gets passed on to each of its daughters so the genotype is more important than the phenotype. In sexual reproduction, the phenotype is more important

because only half of the organism s genome gets passed to the next generation. Fitness is not related to longevity but is instead related to the ability to pass on the genes to the next generation. Fitness is measurable but isn t an exact number but is a probability that the genotype or phenotype will get passed on. It is a property of a population of a species rather than of an organism itself. An individual can have a genotype that is greater or less than the fitness of the total population. Reproductive success is an organism s individual production of offspring per lifetime or per breeding attempt. It is not limited to the number of offspring that a single individual creates but also relates to the number of offspring that the offspring themselves make. A long life is not necessarily related to reproductive success. A major factor in reproductive success is the parental investment an organism makes in order to ensure that the offspring have a better chance themselves of reproductive success. Mate choice and sexual selection are also important in reproductive success. Reproductive success is measured in longitudinal studies because it is measured over several generations. Nutrition is important in reproductive success. The amounts of certain nutrients taken in at certain times of an organism s lifespan will play a role in the organism s ability to be reproductively successful. This is true of many types of species. A lack of nutrients can adversely affect the organism s mating capacity. Insects and mammals both are affected by the amount of protein, fat, and carbohydrates in the diet. Nutrition is most important in the premating time period in many mammals. For some, it is the carbohydrate content that is important, while in others, it is the protein content. In humans, there is an advantage to cooperative breeding, which helps in the investment required to raise a child to adulthood. It takes parental involvement and non-parental involvement. Throughout history, women have a greater reproductive success rate than men. Women have a greater investment in their offspring from the beginning. Males do not have a great investment in the offspring from an evolutionary standpoint. In the hunter-gatherer environment, adequate birth spacing helped to ensure the better survival of each of the offspring.

STUDYING NATURAL SELECTION In the study of natural selection, there are many examples of how natural selection has played a role in the development of certain adaptations. Skeletal adaptations are one example. Think about the skeletal adaptations that have taken place in lizards and giraffes. Giraffes evolved to have long necks so they could reach vegetation high in the trees. The tradeoff for animals with short necks was that they died off. The tradeoff for the giraffe was that they must expend extra energy to support their neck. Lizards developed longer legs to get up out of the water in order to escape flood conditions. Coloration is adaptive to certain species, particularly in mating. The growth of peacock feathers in males allows for enhancement of mate selection among peacocks. We have already discussed natural selection as it occurred in the coloration of peppered moths in the Industrial Age. Bacteria are often studied by researchers when it comes to evolution because evolutionary changes in bacteria happen much more rapidly than other organisms. The fact that they go through several generations in a single day can help researchers see how evolutionary pressures can affect these large populations of microorganisms. Antibiotic resistance is one of the major areas of study in bacterial populations. Humans have evolved to digest cows milk but to varying degrees. In parts of the world where cattle are raised and milk is used in the diet, the humans have a higher incidence of having the enzyme lactase, which is necessary for milk digestion. If milk is not a big part of the diet, most of the individuals who live in those environments are lactose intolerant and cannot digest cows milk carbohydrates.

NATURAL SELECTION AND COMPLEX BEHAVIORS The study of natural selection as it applies to complex behaviors is referred to as evolutionary psychology. It looks at human behavior as it applies to human evolution. These researchers look at thoughts, responses, and emotions from an evolutionary standpoint. This is based on the idea that humans have instincts just like other animals do. Ancestors of modern man used their intelligence and instincts in order to solve common problems. These abilities allowed ancient man to solve problems and arrive at successful solutions that could, in turn, affect their ability to be reproductively successful. Making friends and having trust are

common-sense things that give humankind an advantage. Evolutionary psychologists believe that some of these things are inherited and instinctual. There are certain principles followed by evolutionary psychologists. These are the major principles followed by these researchers: •

The brain is a physical structure that affects behaviors that may or may not be adaptive.

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A person’s brain circuitry helps in solving problems.

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Psychological behaviors are largely subconscious, even though your thinking is a conscious thing.

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There are complex neural circuits that help humans solve problems more adaptively.

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Modern mind has adaptive changes that originated at the dawn of mankind, when humans were hunter-gatherers.

Language is something that humans have evolved to be able to do. Language is a complex behavior that was once and still is beneficial for human survival. Language acquisition has evolved and advanced over time because of natural selection. In modern times, language leads to increased popularity, better wealth, safety, reproduction, and survival. Phobias may be explained by evolution. While phobias are considered irrational, most phobias are based on fears of things that were once more dangerous to mankind, such as spiders, snakes, tigers, and lions. They allowed ancestors to be more wary of things that could easily be hidden in the environment.

KEY TAKEAWAYS 1. Natural selection involves a greater survivability of a species that has adapted to the environment. 2. Adaptations can be helpful, harmful, benign, or vestigial. They can involve structural, physiological, or behavioral changes in the organism. 3. Reproductive success is the success in not only reproducing yourself but the subsequent reproductive success of the next generations. 4. Mimicry involves looking or behaving like another organism in order to confer an advantage to the species. 5. Evolutionary psychology involves the probability that behaviors in humans and higher animals are somewhat instinctual and based on what was successful in the huntergatherer society.

QUIZ 1. What does natural selection least depend on? a. Adaptation to the environment b. Reproductive success c. The size of the population d. Competition for resources Answer: c. Natural selection depends on each of these things but it is least affected by the size of the population undergoing natural selection. 2. The physical characteristics of an organism is called what? a. Phenotype b. Genotype c. Genome d. Mutational trait Answer: a. The phenotype involves the characteristics of a specific organism. It is based on its genome or genotype and can change because of mutations in the genome from the time of birth. 3. What term best describes the phenomenon of selective breeding in domesticated animals? a. Sexual selection b. Artificial selection c. Trait analysis d. Formation of an ecological niche Answer: b. Selective breeding is a type of artificial selection that is done with the purposes of choosing traits that are desirable and breeding those animals with the desirable traits.

4. What do researchers in evolutionary developmental biology or evo-devo actually study? a. Changes in phenotype among populations of organisms b. Genetic variations between organisms of the same species. c. Protein differences between different species. d. The developmental changes that occur in embryos. Answer: d. Researchers in evolutionary developmental biology or evodevo study the relationships in the organisms by looking at the developmental changes within embryos themselves. 5. What type of selection is happening with the differences in plumage among male peacocks? a. Ecological selection b. Kin selection c. Sexual selection d. Gametic selection Answer: c. Sexual selection is the choosing of a sexual mate over others of the same gender. This is what happens when female peacocks choose a sexual mate on the basis of the male s plumage. 6. Competition among members of the same gender for mates of the opposite gender is referred to as what? a. Intrasexual competition b. Intersexual competition c. Gametic selection d. Fecundity selection Answer: a. Intrasexual competition is that which occurs among members of the same gender in order to be more attractive to the opposite gender.

7. Which type of adaptation is not helpful for an organism’s survival? a. Deleterious adaptation b. Structural adaptation c. Physiological adaptation d. Behavioral adaptation Answer: a. Each of these adaptations can be helpful for the survival of an organism but a deleterious adaptation will not be helpful and will reduce the chances of survival. 8. What is not a physiological adaptation in an organism? a. The making of venom b. The capacity to learn c. The ability to regulate temperature d. The making of slime Answer: b. Each of these is a physiological adaptation except for the capacity to learn, which is a behavioral adaptation. 9. The phenomenon of a trait that was once adaptive but is no longer adaptive or may be maladaptive is called what? a. Pre-adaptation b. Spandrels c. Deleterious adaptations d. Vestigial adaptations Answer: d. Vestigial adaptations, like the appendix and wisdom teeth, were likely once functional but are no longer serving any helpful function.

10. The phenomenon of a trait that does not appear to have any specific function in an organism is called what? a. Pre-adaptation b. Spandrels c. Deleterious adaptations d. Vestigial adaptations Answer: b. A spandrel is a trait that does not appear to have any adaptive function in an organism.

CHAPTER THREE: THE STUDY OF TAXONOMY AND PHYLOGENY This chapter talks about the evolutionary relationships between the different types of living things. It starts with a discussion of taxonomy, which is the naming convention used to describe all living things. Every form of life falls under one of three domains, Bacteria, Archaea, and Eukarya. There are other subdivisions that describe these types of arrangements. Exactly how to describe the relationships between life forms involves the discussion of phylogenetic trees. As you will see, newer findings in biology and microbiology have changed the way these phylogenetic trees are arranged.

TAXONOMY Taxonomy is the scientific method of naming and classifying different groups of biological organisms that share certain characteristics. Taxonomy refers specifically to a naming convention, while phylogeny refers to the evolutionary background of a specific organism. A clade is a group of organisms that share a common ancestor and a phylogenetic tree is the tree that has been built to describe the evolutionary background of an organism. Organisms can be grouped into taxa and are given a certain taxonomic rank. There is a taxonomic hierarchy that involves the different rankings of organisms. The largest rank is called a domain. There are three main domains of human life: Bacteria, Archaea, and Eukarya. There is no domain for viruses, which technically aren t living things because they are not cellular. After domains, there are kingdoms, phyla (or divisions in botany), classes, orders, families, genuses, and species. As mentioned in chapter one, Carl Linnaeus first developed the taxonomic system used today. Related studies include cladistics, phylogenetics, and systematics; these are all ways that scientists attempt to connect the different organisms as they relate to one another in terms of the evolution of species. All organisms, plants, and animals have a genus and species. Humans, for example, are called Homo sapiens, while we understand bacteria and other microorganisms mainly on the basis of their genus and species names, such as Staphylococcus aureus and Escherichia coli. While historically, taxonomy was based on obvious similarities and differences between the different

species, the studies of microbiology and genomes have changed the ways in which these relationships are interpreted. As you have seen, the terms taxonomy, systematics, phylogenetics, systematic biology, biological classification, and scientific classification often have overlapping meanings but each is somewhat distinct from the other in terms of their meaning. Because of the great diversity of living things, taxonomic classifications are very large and complex. Exactly how scientists go about determining what species a particular organism is involves a branch of taxonomy called microtaxonomy”. Where the organism falls in terms of the higher taxonomic ranks is called macrotaxonomy”. Early taxonomy, prior to Linnaeus, was relatively arbitrary. Serious attempts to do these kinds of classifications did not happen until the 1700s. Most of these were descriptive and were only used to describe plant classifications. The Great Chain of Life” theory was based on the idea that there was a common ancestor to all living things. The Ancient Egyptians tried to describe certain medicinal plants from as early as 1500 BCE. Aristotle himself identified certain attributes of living things, including the major divisions of plants and animals. He divided animals into vertebrates and invertebrates, and understood that there were differences in animals if they were egg-laying or gave birth to live offspring. The trend toward classifying plant species continued in the Early Modern Era. The first taxonomist was Andrea Cesalpino, who studied more than a thousand plants in the 1500s. This was expanded in the 1600s by John Ray, who studied thousands of different plant species. Carl Linnaeus lived in the 1700s; he developed a standardized system for naming both plants and animals that is still used today. When Darwin developed his theory on the origin of species, what came along with this was the idea of common descent. Fossil groups were included in tree of life” representations that were popular around the time of Darwin. Dinosaurs were believed to be the common ancestor of birds under this system. Later on, we will talk about cladistics, which is the method that has been used to define certain groups of species in terms of their common ancestors. This allows for the arrangement of the different taxa according a hierarchical evolutionary tree, paying no attention to the different ranks. According to the rules of cladistics, groups that have all of the descendants of a specific ancestor is called monophyletic. Groups that have some of their descendants removed are called

paraphyletic. Groups that span more than one branch of the tree of life is called polyphyletic. In the PhyloCode, which uses clades to understand species relationships, the system is designed to coexist with the ranks used in Linnaean taxonomy. According to Linnaeus, the top rank was plants and animals. The idea of domains is a new one, developed first in 1977 when three domains were developed. Archaea and Bacteria were once considered one domain but, as research progressed, it was clear that there were key distinctions between these two types of organisms so that two domains were made to add to Eukarya. While most people use the three-domain system, there have been other systems proposed since then. Most recently, there is the Cavalier-Smith system, which describes two major empires and seven kingdoms. The seven kingdoms are Bacteria, Archaea, Protozoa, Chromista, Plantae, Fungi, and Animalia. A species name is referred to as a binomial because it is a two-part name. The genus name is always capitalized, while the species name is not capitalized. When written, the binomial is italicized. In some cases, there are subspecies, which will give a trinomial name to the organism. In plants, there are also infraspecific names that are similar to the subspecies names used in the animal kingdom.

PHYLOGENIC TREES Another name for phylogenetic tree is the evolutionary tree. This is a tree or diagram that shows the relationships between species, also referred to as their phylogeny. They can be based on physical similarities or genetic characteristics. The idea is that all life on this planet has a common ancestry so that the tree” is rooted with a common ancestor. Figure 1 shows an example of a phylogenetic tree:

Figure 1.

This concept of a tree of life” is an ancient one, when the ancients referred to the Great Chain of Being”. Charles Darwin illustrated his concept of the tree of life in his book On the Origin of Species. Tree diagrams are still used today to understand the basics of evolution. In modern times, the classification of species is now more dynamic and less static. There are different types of phylogenetic trees. In a rooted tree, there is a single node that represents the most recent common ancestor with descendants making up the leaves of a tree. In an unrooted tree, the relatedness of the different leaves is made clear but there isn t any assumption about a common ancestor. It helps to identify ancestry and some of them involve speculation about the time period between ancestral splits, which is based on the molecular clock hypothesis we talked about in chapter one. Both the rooted tree and the unrooted tree can be bifurcated or multifurcated. A bifurcated tree has two descendants that arise from a specific interior node. A multifurcated tree has more than one descendant coming from an interior node. Another name for a phylogenetic tree is a dendrogram. There are other types of trees that are sometimes used. A cladogram does not have ancestors on its internal nodes. A chronogram is a tree that indicates a timespan between the branches. A Romerogram is a representation of evolution as a whole but isn t an evolutionary tree. Trees themselves have their limitations so sometimes a phylogenetic network is used instead. The problem with phylogenetic trees is that they aren t necessarily correct. There can be horizontal gene transfer, hybridization, or genetic recombination between species that give them genetic similarities that they wouldn t otherwise have. So, how are phylogenetic trees built? The basic idea is that organisms descend from other organisms but with modifications made that make them unique from the ancestor. Scientists look at the patterns of these modifications in order to determine who the common ancestor is. They look at the different modifications that have occurred over time in order to see which modern or ancestral species was the original species. The novel traits or the most recent traits that are different from the ancestor are called the derived traits, which are different from the ancestral traits. Features that are gained or lost can be derived traits; they do not have to be an addition to the ancestor. The goal is to determine which traits are derived and which traits are ancestral. These traits can be physical, biochemical, or behavioral.

Another goal is parsimony, which means that one looks at the simplest explanation or the simplest path from the ancestor to the descendants. The right tree is probably the one that has the fewest number of independent genetic events in the process of drawing the tree. One problem in looking at the different features in a phylogenetic tree is that there can be homologous features that have a shared ancestry and analogous features that look similar but arose completely independently from each other. Evolution can also work backward so that a gained trait can just as easily be lost in the future. DNA sequencing is just one more recent tool that can be used to build phylogenetic trees. Related genes in different organisms are compared to see how similar they are to one another and to see what pattern best reflects the common ancestor.

CLADISTICS Cladistics is another way of classifying organisms and is the most commonly used method in today s time. It is an overall classification system that categorizes groups of plants or animals into clades, which is based on the most recent common ancestor of the group. It is determined by looking at the derived characteristics that can be seen in the group s most recent common ancestor. Figure 2 shows the clade involved in human skull formation:

Figure 2.

Willi Hennig was an entomologist who first wrote a book on cladistics in 1966. It has been used to some degree since 1901, when it was applied to birds. It was later applied to insects and to plants. It was originally used to describe differences in structural characteristics but, when the polymerase chain reaction or PCR testing was developed in 1990, the use of DNA characteristics to define relationships between organisms became more popular. Computers are used to identify DNA differences and similarities. What gets created when cladistics is used is called a cladogram. This looks like a tree that best hypothesizes the evolutionary relationship between organisms. As mentioned, genetic relationships are now more commonly used to do this than morphological characteristics. We spoke of parsimony in the creation of phylogenetic trees. Because of the accuracy of DNA sequencing, parsimony is no longer completely followed and cladograms can be more sophisticated. Interestingly, when different pieces of data are used, the cladograms produced can be different and confusing. There are certain terms used to describe the character states within members of a clade. A plesiomorphy is the ancestral state that has been retained by the descendants of the ancestor. A symplesiomorphy is a character state that is different among members of a clade, even though they are related. Cold-bloodedness in reptiles and warm-bloodedness in birds are different phenomena, even though these are closely related organisms. In such situations, warmbloodedness is a new feature, called a symplesiomorphy. An apomorphy is a new innovation or derived state within a clade. It can be used to name a clade. Clades are identified by the synapomorphies, which are shared within a clade, while autapomorphies are traits that do not show a relationship between clade members. A synapomorphy can be something like having digits that helps to define the clade. Any characteristic that is seen in at least two descendants but is not seen in the common ancestor is called a homoplastic state. Mammals and birds are both warm-blooded but the common ancestor was not warm-blooded. They also represent different smaller clades but are part of a larger clade. Because it was developed independently from one another, warmbloodedness in mammals and birds is not a synapomorphy. Instead, warm-bloodedness in these two groups is considered a homoplasy that does not identify these two organism types as part of a clade. So, basically, an apomorphy is something that each member of a clade has in a monophyletic clade, unless the organism subsequently lost the apomorphic trait. If there is at least one plesiomorphy in a clade that was not inherited by all of the descendants, it is called a

paraphyletic clade. This type of clade is truncated so that some of the descendants have been removed because of differences in their characteristics. Polyphyletic clades have at least one homoplasy in the clade members that hasn t been inherited by a common ancestor.

PHYLOGENETICS AND MOLECULAR PHYLOGENETICS As mentioned earlier, phylogenetics is a way to study the evolutionary relationships between different species. Observable traits, DNA sequences, and protein sequencing are used to define most of the different relationships. Computers are commonly used to increase the likelihood of finding the most accurate relationships between descendants. In the late 1800s, the idea of recapitulation was established when it comes to phylogeny. The common expression was ontogeny recapitulates phylogeny”, which indicated that the embryonic growth of an organism closely mirrored its evolutionary pathway. This theory is not longer considered valid. Molecular phylogenetics is related to molecular evolution. In molecular phylogenetics, hereditary molecular differences and genetics are used to understand an organism s relationship to other organisms. It helps to understand what s behind the diversity of the different species. Molecular evolution suggests that mutations in certain genes, leading to protein changes, have affected the structure or morphology of the different descendant organisms. Phylogenetic trees can be developed from these biochemical data. Orginally, things like carbohydrates, enzymes, and proteins were used to identify differences in the descendant organisms. Much later, DNA sequencing was instead used to get at the source of these differences. This process is long and expensive if it makes use of the entire genome of the organism. Instead, certain chromosomes and DNA sequences are looked at instead of the whole genome. The idea is that, over time, there have been mutations in key DNA segments that have resulted in diversity among the different organisms. There will be DNA segments preserved over time that have come from the ancestor and segments that have changed. The percent divergence or percent of substitutions of base pairs in a DNA sequence will be used to define the disparity between the organisms. Multiple key sequences are used in the comparison. Clades are defined by their similarities in DNA sequences. DNA sequences provide a better determination of the molecular clock or the time that the divergences happened because genetic mutations tend to happen over a relatively steady period

of time and at a constant rate. In some cases, the proteins are used to identify divergences rather than the DNA sequences. In determining and identifying phylogenetic trees of different organisms, first the sequence is gotten through biochemical techniques. The sequences are then aligned to make comparisons and substitutions are uncovered. From this, the phylogenetic tree is built and evaluated. The main limitations of using molecular methods to determine a phylogenetic tree is that it cannot always identify when portions of the tree have later come together rather than always diverging. It is also limited by horizontal gene transfer, which mainly occurs in microorganisms. It also assumes a single common ancestor or a rooted tree” and assumes a constant molecular clock, which may not be the case.

KEY TAKEAWAYS •

Taxonomy is a way of establishing the naming of organisms in terms of their ranks in different categories.

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The most often used system of taxonomy involves three domains: Bacteria, Archaea, and Eukarya.

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Phylogeny refers to the evolutionary relationships between different organisms.

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Phylogenetic trees can be created using morphology, biochemistry, or genetics of different organisms.

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The molecular clock theory looks at the timing of different evolutionary changes over time.

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Cladistics looks at clades, which are groups of organisms that share a common ancestor.

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Molecular evolution looks mainly at the DNA sequences in an organism in order to find out when there were divergences in the genetics of the different descendants of an ancestor.

QUIZ 1. The naming convention used to describe a specific organism or group of organisms most refers to what? a. Cladistics b. Phylogenetic tree c. Phylogeny d. Taxonomy Answer: d. Taxonomy refers specifically to the naming convention used to describe specific organisms based on their shared characteristics. 2. What is a group of living things called that share a common ancestor? a. Clade b. Phylogenetic branch c. Taxonomic classification d. Phylogenetic organization Answer: a. A clade is a group of living things that share a common ancestor. Cladistics is the study of these types of relationships. 3. What was the first taxonomic systems in the world used to describe? a. Subtypes of animals b. Subtypes of fish c. Subtypes of microorganisms d. Subtypes of plants Answer: d. The ancient Egyptians used rudimentary taxonomy to try to identify subclassifications of medicinal plants.

4. Aristotle was able to make broad strokes in dividing living things in Ancient Greece. What were the two main classifications of organisms he developed? a. Crustaceans and non-crustaceans b. Plants and animals c. Egg layers and non-egg layers d. Cold-blooded and warm-blooded Answer: b. Aristotle did a great deal to understand the taxonomic relationships between living things, ultimately dividing living things into two large groups: plants and animals. 5. What is most true of phylogenetic trees? a. They are rooted and show a common ancestor to all life forms. b. They are not always accurate because of things like hybridization and horizontal gene transfer. c. They can tell about how long ago the different nodes on the tree broke off from one another. d. They are more like a network rather than any type of tree formation. Answer: b. Phylogenetic trees are not very accurate because even unrelated organisms can share genetic characteristics because of things like hybridization and horizontal gene transfer. 6. Similar traits between species that arise from the same common trait in an ancestor are called what? a. Homologous traits b. Analogous traits c. Derived traits d. Ancestral traits Answer: a. Homologous traits are similar traits between species that come from the same common trait in an ancestor.

7. In a clade, what term represents the characteristic that does not define a clade because they are not shared by members of the clade? a. Plesiomorphy b. Autapomorphy c. Apomorphy d. Symplesiomorphy Answer: b. An autapomorphy is a trait in a clade member that is unique to an organism because it does not relate to what the major similarities are within a clade. 8. A trait that is the same in two organisms as being the same but was not actually inherited by a common ancestor is called what? a. Plesiomorphy b. Apomorphy c. Autapomorphy d. Homoplasy Answer: d. A homoplasy is a trait that two modern descendants had but that was not inherited by a common ancestor. An example is warmbloodedness, which is seen in birds and humans but is not because they share a common ancestor. 9. What is the current type of molecule looked at in terms of identifying the phylogenetics of an organism? a. DNA b. Proteins c. Carbohydrates d. Lipids Answer: d. Earlier studies used chromatography of things like proteins and carbohydrates to identify phylogeny. Nowadays, DNA sequencing is used to make these determinations.

10. Which statement is not true about molecular phylogenetics in the determination of an organism’s phylogeny? a. The entire DNA genome of the organisms is used to make this determination. b. Similar DNA sequences can help to identify a clade. c. The percent divergence is the difference in DNA base pairs or number of substitutions that have happened over time. d. Key segments of DNA are evaluated across different organisms. Answer: a. Each of these statements is true except for the statement that entire DNA genomes are used. This would be expensive and time consuming; it is not necessary to do this either.

CHAPTER FOUR: GENETICS AND GENETIC VARIATION This chapter discusses genetics and genetic variation. Genetics works on a small scale in the inheritance of certain traits by a descendant from a direct ancestor. It also works on a large scale because it is through a series of genetic mutations that new species are ultimately created. We will talk about Mendelian genetics, the science of mutations, and the advantages and disadvantages that come with certain genetic situations.

INTRODUCTION TO GENETICS In order to understand genetic variations, we need to first talk about genetics in general. Genetics is the study of heredity and, in particular, how genes are connected to heritable traits. While heredity and genetics has been understood to some degree for a long time, modern genetics was introduced to the Western world by Gregor Mendel, who was a 19th century Augustinian friar. He studied how specific traits were inherited from a parent to its offspring. This was done without an understanding of what genes and chromosomes are. Genetic material is coded in the nucleic acids of the body. In all forms of life, except for viruses, the nucleic acid that forms the genes is called DNA or deoxyribonucleic acid. It exists in long chains called chromosomes. Bacteria generally have a single circular chromosome, while other forms of life have linear and multiple chromosomes. Chromosomes contain genes. Genes are the basic unit of inheritance. If a particular gene is passed on, the trait is usually passed on, even though it might not be seen as part of the phenotype of the organism. The genome is the entirety of the cell s genes and chromosomes. Genes are made up of numerous base pairs, which are molecules that form a sort of code that determines what the protein made by the gene will look like. The sum total of the proteins, carbohydrates, lipids, and other molecules made or used by a cell or organism determines the structure and function of the cell.

HISTORY OF GENETICS The concept that living organisms inherit certain traits from their parents has been known since ancient man practiced selective breeding of plants and animals. Before Gregor Mendel, genetics had been studied but not in the detail that it was studied by Gregor Mendel. Initially, the concept was that the offspring had the average of the characteristics of the parents but this would not have made evolution possible through natural selection. This was called blending inheritance”. Remember, too, that Lamarck felt that acquired characteristics could be inherited from the parents. Pangenesis was the belief system of Darwin, who felt that both acquired and innate traits could be inherited. Mendel himself believed that there were dominant traits and recessive traits inherited from parents. He mathematically studied pea plants and their patterns of inheritance. He wrote a paper in 1865 on the subject but this was not widely disseminated until 1900. It was discovered in 1911 by Thomas Hunt Morgan that genes were located on chromosomes. He studied fruit flies and sex-linked inheritance. Soon after, it was determined that genes lined up along a chromosome. Chromosomes are made from DNA and related proteins but it wasn t clear that it was the DNA responsible for genetic traits. Transformation, which is the transfer of genetic material from dead bacteria or from the environment to living bacteria, was discovered in 1928. James Watson and Francis Crick discovered the nature of DNA structure in 1953. It was determined to be a double-stranded helix. Figure 3 shows the typical structure of a DNA molecule:

Figure 3.

It was then determined that the double strands could be separated and copied in the process of DNA replication. This means that DNA is semi-conservative; one strand provides the template for the making of the other strand.

GENETIC PROCESSES Through complex processes of transcription and translation, the genetic code is made into proteins. Transcription involves the copying of the DNA segment into ribonucleic acid or RNA. Translation is when the RNA message gets turned into a protein segment. Most recently, the human genome has been sequenced and the polymerase chain reaction was developed, which is a technique for amplifying and identifying DNA sequences. The patterns of inheritance can be determined by doing a genetic pedigree. This is a drawing that looks and the male and female parents, their offspring, and their own offspring. This can be done through many generations, highlighting which individuals in the pedigree carry the trait or disease state. Often, the pedigree will show the different patterns of inheritance of a particular trait or disease. Some genetic traits are the result of multiple genes, such as the height of one s offspring. These are called polygenic traits. This makes it more difficult to draw an actual pedigree chart. In many cases, scientists do not know exactly which genes get involved in the determination of the end result in the offspring. Remember that humans, and many multicellular eukaryotic organisms reproduce sexually so there are traits that can be passed on from both parents to each of their offspring. There are also complex traits that not only involve many genes but yield offspring that have features on a continuum between the two parents. This is true of human skin color. It doesn t mean that these are not heritable but rather that the actual inheritance of the feature is more complicated than can be explained by one gene. Heritability is the degree to which genetic factors determine a specific trait. Human height is an example of something that isn t 100 percent heritable. This is because the environment, such as nutrition, also plays a role in the end result. As mentioned, DNA is what makes up genes. DNA is itself made of nucleotides, which are a type of molecule that can easily form chains. There are four different nucleotides that make up DNA. These are adenine, guanine, cytosine, and thymine. The arrangement of the nucleotides determines the protein made by the gene. Figure 4 shows what the nucleotides look like:

Figure 4.

As you can see by the figure, adenine combines with thymine and cytosine combines with guanine. When these are on opposite strands of DNA, they create a sort of ladder with rungs that makes up the DNA structure. This means that one strand can be used to copy its opposite strand. The longest human chromosome is about 250 million base pairs or nucleotides long, with hundreds or thousands of genes per chromosome. There are proteins that support and organize the DNA so that the whole chromosome structure is called chromatin. Most organisms are considered diploid, which means that they contain two copies of each chromosome. This is not the case with haploid organisms like bacteria, that have just one copy of the chromosome. Gametes, or sex cells, are haploid because, when they come together in the offspring, the offspring will be diploid. Each separate gene on one chromosome is called an

allele. For traits that are passed on with a single gene, one allele is given by each parent to make two alleles in a diploid organism. An allele can be dominant, recessive, or codominant. Some are sex-linked or X-linked and affect primarily boys, because they have just one X chromosome so they cannot have a normal allele on a second X chromosome. This is the case with girls that have two X chromosomes. Organisms can divide sexually and asexually. The process of mitosis is when a cell divides itself into two daughter cells that are identical to the parent cell. These daughter cells are called clones. Mitosis represents asexual reproduction of the cell. Bacteria do this as part of their reproductive process, although it is called binary fission. Eukaryotic organisms may or may not be involved with sexual reproduction. This involves the making of a haploid sex cell that combines with the haploid sex cell of the opposite gender to make offspring that have mixed patterns of DNA and that are diploid like the parent cells. A gamete is a sex cell, which can be either a sperm cell or an egg cell. Bacterial cells can take up new genetic material in ways that are not the same thing as sexual reproduction. Conjugation involves taking up a piece of DNA from another bacterium, while transformation involves the uptake of DNA from the environment. This is what is meant by horizontal gene transfer. You should know that chromosomes in the sex cell do not get transferred unchanged from parent child. If this was the case, all offspring would be identical in form and appearance. There is genetic recombination that takes place, which basically shuffles the DNA on homologous chromosomes. This is also referred to as chromosomal crossover. It happens in the process of meiosis, when a diploid germ cell becomes haploid in order to make a sex cell. If two genes are far apart, their crossover rate is higher. With genetic linkage, two genes are so close together that they get inherited together. As we talked about, genes and DNA serve to provide a template used to make proteins. The genetic code is made from a set of three nucleotides in a row, called a triplet code or codon. Each codon makes up the code for a certain amino acid. There are 20 amino acids that make up the structure of proteins. It takes a messenger RNA molecule to turn the DNA into a message that is read in order to make proteins. We will talk later about mutations, which are mistakes in the DNA structure. Mistakes can be substitutions in the nucleotide sequence, deletions of a gene, or additions to the gene. Some can make very little difference to the organism, while others can be extremely deleterious. Genetic

diseases often happen because of mutations in one or more genes. Sickle cell anemia, cystic fibrosis, and muscular dystrophy are all genetic diseases that come from gene mutations. While most phenotypes in an organism are inherited, there is some contribution of the environment in determining the actual phenotype. This is true for diseases like phenylketonuria, which is a problem in the metabolism of the amino acid called phenylalanine. Without phenylalanine in the diet, the person does not have characteristics of the disease. Even identical twins do not have 100 percent heritability as it applies to getting certain diseases. This is why twin studies are used to determine just how heritable a disease process is. While every cell of a multicellular organism contains the same DNA in their genome, not all cells are the same in the organism. This is because of differences in gene regulation. There are certain transcription factors that determine what genes get expressed and those that do not. This process of regulation can be complex and can involve factors that promote a gene s expression and those that inhibit a gene s expression. There are signals within a cell and around the cell that determine what the cell s function is in a multicellular organism. Mutations play a role in natural selection. Most mutations either have no effect or are detrimental to the organism. Some, however, can be beneficial to the organism. This is where natural selection plays a role in genetics. If a mutation is beneficial and confers an advantage to the host, the mutation could be selected for and the frequency of the mutated gene would increase in the population. There are certain organisms studied more frequently than others in the study of genetics. Most of these organisms are easy to grow, have short generation times, known genotypes, and easy manipulability when it comes to their genome. Some of these include Escherichia coli, baker s yeast or Saccharomyces cerevisiae, certain plants, mice, fruit flies, and some nematodes.

MENDELIAN GENETICS Mendelian genetics is a way of understanding inheritance according to laws of genetics outlined by Gregor Mendel. They serve as the main model for how genes get transferred from parents to offspring in both plants and animals. As mentioned, Mendel studied pea plants and hybridized them as part of his studies on inheritance. His work determined that inheritance is discontinuous rather than blended or continuous. Mendelian genetics is also referred to as classical genetics. Out of his studies came Mendel s laws. He bred purebred purple and white pea plants to make what was called the F1 generation. Because these were purebred, they carried two copies of the same gene for flower color. The end result was that all flowers in the F1 generation were purple. He determined that purple color was a dominant trait. Figure 5 shows a Punnett square:

Figure 5.

He then looked at the progeny or offspring of the F1 generation to make an F2 generation. Because the F1 generation consisted entirely of heterozygous alleles, the end result was a ratio of purple to white flowers that was three to one. A homozygous organism has identical copies of the same allele, while a heterozygous organism has two different copies of an allele. Remember that Mendel did not know anything about genes or alleles. Instead, he called the genes factors” and alleles were forms of the different factors. According to Mendel, these pairs of alleles separated independently and inherited one from each parent. This observation led to the Law of Segregation and the Law of Independent Assortment. According to the Law of Dominance, some traits are considered dominant over others. Recessive traits only get expressed if they are homozygous. If the dominant allele or trait is at all a part of the organism s makeup, the phenotype will be that of the dominant trait. An organism with a dominant trait may be homozygous or heterozygous for the trait but one would not be able to tell the difference because the recessive trait is effectively hidden. Mendel s first law is the law of segregation. It states that each organism has two alleles for each trait that completely separate during the making of sex cells or gametes. The second law is the law of independent assortment. It means that the different gametes are equally likely to be fertilized. Two separate alleles inherited by the offspring will be inherited separately. This is the law most likely to be violated because of the phenomenon of genetic linkage that we just discussed. The third law or the law of dominance says that a recessive trait will always be hidden by a dominant trait. This law may be broken but this is uncommon. Are there instances of inheritance that can be non-Mendelian? As it turns out, there are. In the case of complete dominance, the offspring are of the dominant phenotype, even if they are heterozygous. In some cases, there can be incomplete dominance, where there is an intermediate to being dominant or recessive. There is codominance, where both the alleles get equally expressed. The ABO blood type in humans is an example of that. There are also multiple alleles. There will still be one allele per parent but the choices of alleles are more than two. In polygenic inheritance, many genes play a role in the inheritance pattern.

GENETIC VARIABILITY AND MUTATION Genetic variability or genetic variation involves the differences in DNA among individuals. If there was no genetic variation, the organisms of the same species would always look alike. Genetic variation can be seen phenotypically, found through biochemical differences, or seen in the DNA sequencing of the organisms. Geographic variation can be seen in populations that are of the same species but do not look alike. This is because of genetic drift. Most genetic variation is caused by random mutations. There are a number of ways to maintain genetic variation in a population. Because of heterozygosity, alleles that may be harmful and that are recessive can be somewhat hidden. Natural selection also favors genetic variation. Genetic variation can be helpful because it promotes biodiversity. Other things that can cause genetic variability include the following: •

Recombination among homologous chromosomes.

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Movement into or out of a population.

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Polyploidy, which is having more than two of the same chromosomes.

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Genetic mutations that have a positive effect on fitness.

In actuality, mutations happen all the time. About 60,000 mutations occur every day in human cells in each cell but the majority of these are repaired with DNA repair mechanisms. Things that decrease genetic variability include the following: •

Fragmentation of the habitat of an organism.

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The founder effect, in which a population is founded by just a few individuals.

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Climate change, which decreases the size of populations and lowers variability.

Evolvability is when a system or population is able to undergo adaptive evolution. This allows for evolution through natural selection. If beneficial mutations do not happen often enough, adaptation can t occur. Sexual reproduction causes more evolvability than asexual reproduction. Selection is better and is enhanced because of things like mating rituals that increase sexual selection, having a large population size, short generation time, and recombination.

MUTATIONS We have talked a little bit about mutations. These are changes in the nucleotide sequence of a gene in a genome. This issue can happen because of errors in DNA replication, carcinogen exposure, or exposure to radiation. Not all mutations are noticeable but these are linked to things like cancer, evolution, and immune functioning. Mutations may involve the duplication of very big sections of DNA because of genetic recombination. Changes in chromosome number, as is seen in polyploidy and aneuploidy, can cause large mutations, some of which aren t compatible with life. In other cases, it can result in a new species. Transposons are segments of DNA that are able to move within the genome. Certain mutations may be favorable to the individual having the mutation. Neutral mutations are those that do not affect the organism s fitness but can lead to genetic drift. Small-scale mutations just affect one or a couple of nucleotides. Point mutations affect one nucleotide only. Insertions happen when one or more nucleotides are added to the genome. Deletions happen when one or more nucleotides are removed from the genome. Substitution mutations happen when one nucleotide gets exchanged for another. If a mutation adds or subtracts just three nucleotides, the effect is not as great as if more or less than three nucleotides are added or subtracted. This leads to a frameshift mutation, where the reading of the rest of the gene is incorrect. This is because codons happen in groups of three. Large-scale mutations affect large sections of the chromosome. Chromosome translocations happen when there is exchange of genetic material from one type of chromosome to another. Inversion happens when the direction of the genome is reversed. A mutation can inactivate a protein. This usually is a recessive trait. Gain of function mutations will increase the activity of a protein. Dominant negative mutations make an altered gene product that is antagonistic to the cell. Lethal mutations will kill the cell. Deleterious mutations can decrease the organism s fitness, while advantageous mutations increase the organism s fitness. Examples of beneficial mutations include one for HIV resistance in some Europeans, who may also have had resistance to the bubonic plague in the 14th century. Malaria resistance is conferred by people who are heterozygous for sickle-cell anemia. The ability to digest lactose is a beneficial mutation in humans. Antibiotic resistance in bacteria is beneficial to the organism.

KEY TAKEAWAYS •

Genetics helps to explain how certain traits are passed on from parent organisms to offspring.

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The genetic blueprint is DNA. Genes are the smallest unit of heritability; these all together make up the genome of an organism.

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All cells in the multicellular organism contain the same genes but these are expressed differently in different cells.

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Mendel worked with pea plants and determined the different laws of inheritance.

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Genetic variability can be due to several things that usually are beneficial to the population.

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Mutations are largely deleterious or neutral; however, some can be advantageous and will be selected for in the process of natural selection.

QUIZ 1. Which type of organism does not necessarily have DNA as its main genetic blueprint material? a. Bacteria b. Archaea c. Eukaryotes d. Viruses Answer: d. Viruses may contain DNA or RNA as their major form of nucleic acid. Certain viruses do not contain any DNA but contain only single-stranded or double-stranded RNA molecules. 2. What is the basic microbiological unit of inheritance called? a. Genome b. Gene c. Chromosome d. Base pair Answer: b. The gene is the basic unit of inheritance. Genes are either passed on intact or not passed on as part of the hereditary process. 3. What type of allele is seen in only one gender because of having two different chromosomes as part of their DNA? a. Sex-linked b. Dominant c. Recessive d. Codominant Answer: a. A sex-linked allele leads to a trait seen in only one gender because the gender has just one X chromosome and not two.

4. What is the general name of the haploid cell of an organism that is used for reproduction? a. Egg cell b. Sperm cell c. Gamete d. Clone Answer: c. A gamete is a sex cell that combines with a gamete of the opposite gender to make a diploid zygote, which grows into an embryo and into an adult organism. 5. How does natural selection play a role in genetics and heritability? a. It ensures that all weaker organisms die out. b. It uses epigenetic factors to control gene regulation. c. It increases the frequency of an advantageous mutation. d. It does not play a large role in heritability. Answer: c. Natural selection will result in an advantageous mutation increasing in frequency in the population, which could cause enhanced selection for the mutated organism. 6. What organism did Gregor Mendel study? a. Mice b. Fruit flies c. Algae d. Pea plants Answer: d. Gregor Mendel studied and cultivated pea plants in order to see how they cross-bred or hybridized as part of his study of genetics and how genes are passed on.

7. Which of Mendel’s laws are most likely to be violated in real life genetic situations? a. The law of segregation b. The law of independent assortment c. The law of dominance d. None of these laws can be violated Answer: b. The law of independent assortment gets violated when two genes are so close together that they are inherited together due to genetic linkage. 8. What is it called when there are more than two choices of alleles that can be inherited? a. Complete dominance b. Incomplete dominance c. Polygenic inheritance d. Multiple allele inheritance Answer: d. In multiple allele inheritance, there are more than two types of alleles that can be chosen from and inherited. Each parent will still carry a single allele but there are simply more choices of alleles that are possible. 9. Which type of mutation affects the greatest amount of the genome? a. Aneuploidy b. Chromosome inversion c. Frameshift mutation d. Substitution mutation Answer: a. Aneuploidy is a large mutation because it causes the whole chromosome to be missing in later generations.

10. The addition of which number of nucleotides in a mutation will lead to a frameshift mutation? a. Three b. Five c. Six d. Nine Answer: b. As long as the addition or deletion affects a multiple of three nucleotides, it will not cause a frameshift mutation.

CHAPTER FIVE: ORIGIN OF LIFE This chapter introduces topics related to the origin of life on earth. Life on earth in the beginning of time was very different than it is now. This is partly due to the fact that the early conditions of earth as a planet were vastly different from that of present-day time. The chapter talks about the evolution of viruses and of prokaryotes, which were the first cells to represent life on this planet.

EARLY EARTH ENVIRONMENT The earliest time on planet earth is called the Hadean period. It is difficult to study this period because of a relative lack of fossil records. Water first appeared on earth and the first life forms developed over time. There are several periods, called eons. Before going further, we will talk about the different eons and the major events that occurred during these times: •

Hadean—this was the first eon and was associated with the formation of the earth.

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Archean—this was when the earth’s crust formed and the oldest rocks existed.

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Proterozoic—this was when life first began in the seas. These were single-celled organism.

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Paleozoic—this was when fish, amphibians, reptiles and early plants developed and predominated.

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Mesozoic—This is when dinosaurs lived and became extinct. The first birds arrived on earth.

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Cenozoic—this is when mammals and mankind predominated the earth.

Earth likely formed in a multi-step process over a period of tens of million years. There was likely an area of protoplanetary gas and dust that coalesced to make a solid structure as these particles collided with one another and stuck together. Growth of the earth itself took millions of years. In the solar system, the moon and Mars developed and became separate bodies. The circular orbit of the earth was established. Earth s molten core took between 10 and 30 million years to form.

Gravitation attraction was likely the reason that the earth grew in size and solid objects in the solar system became the planet we know today. It is not known if there were larger collisions between more than one celestial body contributed to the overall size of the earth. The moon itself may have become attracted to the earth through a collisional event. The geologic time scale or GTS is the way scientists look at the history of the planet. This scale is used because the time periods used to describe early earth are so long. The term Ga” is used to represent billions of years, while the term Ma” is used to describe millions of years. Earth itself is about a third of the age of the universe and is about 4.5 billion years ago. The first atmosphere was probably made from gases emitted from the volcanoes on earth. While it is not 100 percent clear, there was probably little oxygen in the first earth atmosphere. The earth collided often with other celestial bodies and its surface was molten. When a planet-sized body called Theia collided with earth, the moon was created. The Hadean period or eon happened before a fossil record was able to show life. It ended about four billion years ago. Figure 6 shows the different eons on earth:

Figure 6.

In the Archean and Proterozoic eons, the first life forms developed. What followed this was the Phanerozoic eon, which is divided into three eras: The Paleozoic area, with fish and arthropods evolving, the Mesozoic, which involved the non-avian dinosaurs, and the Cenozoic era, which involved the rise of mammals on earth. As a comparison, the first humans came to earth about 2 million years ago. The first evidence of life on earth dates back about 3.5 billion years, during the Archean eon, which would have been just about the time that earth s crust formed. There were fossils of microbes found in sandstone dating to this time period in Western Australia. Graphite, which is a biogenic substance, dates from 3.7 billion years ago in Greenland. The first photosynthetic organisms began on earth about 2.4 to 3.2 billion years ago. These produce oxygen as a waste product of photosynthesis so that the earth became more oxygenated. About 580 million years ago, multicellular life first formed, leading into the Cambrian explosion about 541 million years ago, where life suddenly diversified and become plentiful. About 99 percent of life that once lived on earth has become extinct. There are currently about 10 to 14 million different life forms currently on earth. The earth s crust has changed continually. The process called plate tectonics, which is what separates the continents is still happening today. Pangea is believed to be a single land mass on earth that once connected all of the continents. The earth s atmosphere that harbors life is called its biosphere, while the water habitats on earth are called the hydrosphere. Mankind and activities of humans have played a big role in these areas in recent years. The concept of geochronology involves measuring life in mya, which stands for million years ago. This means that, for the Hadean period, the time was about 4.54 to 4 billion years ago or 45400 to 400 mya. In the Hadean period, earth is formed out of galactic dust, gases, and debris. Life did not exist and the earth was volcanic, extremely hot, and molten. This is when the moon was created and liquid water may have first formed. The Archean eon was between 2500 and 4000 mya. Prokaryotic life first emerged in a process called abiogenesis, which is the formation of life from nonliving molecules. There may have been three separate continents at the time with greenhouse gases and volcanic gases predominating. The Proterozoic period was between 541 and 2500 mya. Eukaryotic life and multicellular organisms existed on earth with oxygen created by living photosynthetic bacteria. Early plants and fungi were developed and there were several ice ages.

The phanerozoic era is from 541 mya to the present time. Complex life developed and the three eons already discussed occurred. There were several mass extinctions, particularly of the dinosaurs; birds and modern mammals developed. Stratigraphic evidence can help to determine the geologic time scale of the earth. There are four major timelines noted, with the first eon taking the most time. This is different from the timetable of life on earth but makes use of basically the same names. The earth developed at the same time as the solar system. It is believed that there were large rotating clouds of gases and dust known as the solar nebula, which was created after the Big bang, which happened about 13.8 billion years ago. There may have been a supernova shock wave that precipitated the coalescence of the earth into solid form and created the rotational properties of the earth. Solar winds blow away excess dust and other debris, leaving behind solid earth material. As the earth grew, it developed a hot, molten material made of metallic substances. These heavy metals sank, resulting in a separation from the molten center and the outer crust of the earth. This also set up earth s magnetic field. There may be a central ice core surrounded by a molten outer core because the earth is cooling. The oldest rocks on earth were found to be 4 billlion years. There are craters noted on other celestial bodies, which have led to the idea that there was a Late Heavy Bombardment that happened around 4 billion years ago. Volcanoes were common, but there is evidence that liquid water also existed around 4.4 billion years ago. The earth cooled but there was no oxygen or ozone layers. The moon is our only natural satellite. Moon rocks have been determined to be about 4.53 billion years old. It is not very dense and has a small metallic core. There is no water on earth. It is believed that Theia, which was about the size of Mars, impacted the earth and stayed in Earth s orbit. This was a huge impact that melted or vaporized the moon and earth s surface. Eventually, the moon became more spherical. The process of plate tectonics happened early after crust formation. Because the earth was hotter, plate tectonics happened at a greater rate. The tectonic plates were smaller but there were more subduction zones. The solid earth s crust likely melted when there was the Late Heavy Bombardment. The earth had three atmospheres. The first contained hydrogen and helium and was captured from the solar nebula. This later got depleted by solar wind, leaving behind gases released by

volvane, which were mainly greenhouse gases. Greenhouse gases include carbon dioxide, water vapor, ozone, methane, and nitrous oxide. Oxygen is not a greenhouse gas and did not exist in high quantities in early earth. Water vapor was probably something that came from asteroids, comets, and meteorites. Clouds ultimately formed and rain cause the oceans to form. Water covered much of the earth in the early Archean period. The sun got hotter and greenhouse gases helped keep the earth warm enough so that it wouldn t be covered in ice. Methane came from early microbes, while ammonia and carbon dioxide came from the volcanoes. Life originally developed in the early oceans. There were probably early chemical reactions that created the building blocks of life, which would have been nucleotides and amino acids. Extraterrestial sources of organic molecules could also have helped form life. Once there was self-replication, the necessary components for life existed. It is believed by some that RNA was the initial nucleic acid used for genetic material. RNA is less stable and was eventually replaced with the more stable DNA. Amino acids can also easily be synthesized by abiotic substances. Amino acids together form proteins and will form small peptide chains in vitro. The process requires high temperatures near the boiling point of water and moderate pressures. This could have occurred near thermal vents deep in the ocean. In order to form cells, double-layered membranes containing lipids needed to be developed. Lipids can form liposomes or bubbles in vitro. Some clays on earth have certain properties that allow for RNA emergence. There are some who support the idea that clay had something to do with the formation of early life on earth. Figure 7 indicates what a liposome looks like:

Figure 7.

While there were probably many protocells in early life forms, only one line survived. The last universal ancestor of all living things existed in the Archean eon about 3.5 billion years ago. It was likely a prokaryote, which will be discussed later in this chapter. It had nucleic acids but did not have organelles. It used DNA and RNA in similar ways as happens in modern bacteria. Some researchers believe that lateral gene transfer was present even as far back as that time. While the earliest life forms absorbed nutrients from the environment, used fermentation, and made energy out of fermentation, this was largely an anaerobic event and did not require oxygen. Photosynthetic organisms changed all that by causing a large increase in oxygenation of the environment. Photosynthetic organisms fix carbon dioxide into organic molecules used for structural and functional elements of the organism. Purple bacteria and green sulfur bacteria do not make oxygen but make other molecules as end products. These tend to live in extreme environments like hydrothermal vents and hot springs, which are usually unhospitable to other organisms. These are very ancient organisms. Stromatolites were the first oxygen-making photosynthetic bacteria. The first oxygen probably oxidized iron in limestone. They later added oxygen to the atmosphere, which became the third atmosphere on earth. Some of the oxygen reacted with UV radiation to make ozone. Ozone

absorbs UV light in the upper atmosphere. This decreases the mutation rate on earth. Oxygen was probably toxic to many lifeforms that existed on earth at the time. Plate tectonics have reconstructed the continents. The tectonic plates have an edge, which is marked by an orogenic belt. There has been more than one supercontinent throughout earth s history. Pangea was the last of the supercontinents. There were at least two snowball earths in the Proterozoic era. These were related to the CO2 levels on the earth, which keep the earth warm.

EARLY FORMS OF LIFE The oldest rocks still found on earth are about 4 billion years old. Evidence of life shows up shortly after that. Fossils of a microbial mat were found in Australia from 3.5 billion years ago. Cyanobacteria in Greenland were discovered dating back 3.7 billion years. These were what stromatolites were made from. Scientists do not know if there were earlier forms of life that did not show up in fossil records. There are no fossil records from the Hadean period. There were many asteroids and meteorites bombarding the planet but life may have existed during this time. Evidence for this is the finding of graphite carbon in crystals of zircon dating from 4.1 billion years ago. Graphite cannot exist without the presence of organic life. Some researchers are skeptical and believe that asteroids could have brought the carbon to earth. As mentioned, the earliest forms of life were prokaryotes. They probably used nutrients like phosphorus from the environment and likely thrived in extreme conditions. There are about 335 proteins that are shared by all modern Archaea and Bacterial organisms, indicating a common ancestor. It indicated also that these were probably anaerobic, living without oxygen, and lived near hydrothermal vents. There are those who believe life originated on earth more than once or that life came to earth on asteroids. Most believe that the earliest organisms were based on RNA instead of DNA. This feature changed over time. No one knows, though, how RNA first came into being. It seems astronomical that RNA could have formed spontaneously. Others believe that it s not so astronomical and that life lives elsewhere in the universe.

VIRAL EVOLUTION Viruses are considered ancient and many are RNA-containing particles. Because they are not cellular, they are not necessarily thought of as life forms by modern scientists. They mutate to a great degree and respond easily to natural selection, resulting in adaptation. Many offspring are made at a time, even though they are not able to reproduce without some kind of host. Mutations get passed to the progeny quite easily. There are many diseases that are caused by viral organisms. Viruses can infect all three domains of life, which may mean they existed at the time of the first universal common ancestor. They have likely arisen many times over the course of history, with new viruses being developed even today. There are three theories about how viruses originated and evolved: 1. Viruses came first. It is possible, because of their simplicity that viruses predated all cellular forms of life. They code for proteins that are completely unrelated to any known cellular proteins but, because they require a host, many do not believe this hypothesis. 2. Degeneracy theory. This is the idea that viruses were once smaller cells that parasitized bigger cells during the course of time. Support for this theory is the presence of larger viruses that have genetics similar to bacteria. It does not explain why small intracellular parasites do not resemble viruses at all. 3. Vagrancy or escape theory. This is the idea that viruses evolved from pieces of DNA that escaped other cells. It doesn’t explain the complexity of viruses in terms of their capsids and other structures. 4. Coevolution theory. This is the theory that says that viruses existed near hydrothermal vents and were able to self-replicate. They evolved at the same time as cells have. 5. Chimeric origins theory. This involves the idea that viruses started out as part of the primordial gene pool, making it a cross between the virus first and escape theories. Viruses mutate to a greater degree than other organisms. This is very true especially for RNA viruses, such as HIV/AIDS. Vital proteins are fold super families that show similar folding even if the DNA sequence is not the same. There are 4 types of fold super families in viruses that correspond with the three domains and one that probably predates the splitting off of the domains. The proteome of a virus suggests it is old indeed.

Viruses cannot form fossils but the genomes of many organisms do contain certain endogenous viral elements that are the remnants of ancient viruses that have inserted themselves into cellular genomes. There are hundreds or thousands of retrovirus sequences in most vertebrates. These help us study the evolution of viruses. They exhibit Darwinian natural selection. RNA viruses mutate more than other viruses because there are no good replication repair processes. Some mutations are lethal, most are silent, but a few are beneficial. Viruses can shuffle their genes so that they can exhibit genetic shift, making them more virulent. Other viruses change slowly over time in what is called antigenic drift. Each of these contribute to the emergence of new viruses. Several virus types have evolved to infect more than one species. Viruses evolve in order to become more infectious. This is enabled by their rapid response to natural selection and rapid mutation rates. Viruses are transmitted through droplets, like sneezing and coughing, airborne transmission, passed through breathing, waterborne transmission, vector transmission, and viruses that can live outside the host. Viruses that are transmitted from mother to child in utero, called vertical transmission, will have lesser virulence than those that are transmitted horizontally from one host to another.

PROKARYOTIC CELL AND EUKARYOTIC CELL EVOLUTION We have talked about prokaryotic cells and eukaryotic cells but have not officially defined them. Prokaryotic cells or prokaryotes are more primitive. They have nucleic acids (DNA) but do not have any enveloped or lipid-bound organelles. Eukaryotic cells or eukaryotes are more complex. They have a cell nucleus that contains their genetic material and have multiple types of membrane-bound organelles. Even with their differences, they did evolve from a single common ancestor that was likely some type of prokaryote. The first cell on earth first occurred about 3.8 billion years ago, which was about 750 million years after the earth itself was formed. No one knows exactly how this happened and it has not been reproduced in a laboratory system. When life first emerged, there was little oxygen on earth but there was plenty of CO2 and nitrogen along with carbon monoxide, hydrogen gas, and hydrogen sulfide. These are conditions that are most optimal for photosynthetic cells. We know that electrical discharges in the presence or inorganic molecules can make amino acids and simple organic molecules. The next step in forming life would have been the making of macromolecules. This can happen under certain conditions of heat in the presence of amino acids. The trick that cannot be

explained is how to get these polypeptides to be self-replicating. Only nucleic acids can selfreplicate so these were necessary for life. Because it has been shown that RNA can catalyze reactions and serve as a template in order to catalyze its own self-replication, it is widely believed that RNA was the original nucleic acid in early forms of life. The time period where this happened is called the RNA world. As we have mentioned, DNA later replaced RNA as the main genetic material in cells. When RNA became enclosed by a phospholipid bilayer, this would have become the first cell. A phospholipid bilayer is necessary for a cell to actually be a cell. Plasma membranes made of lipid bilayers are part of both prokaryotic and eukaryotic cells. Phospholipids are considered amphipathic, which means that they have a water-loving end and a water-hating end. They arrange themselves so that the water-loving end is exposed to the exterior and interior of the cell. Cells also need to metabolize food to make energy. This is something that also had to evolve. All cells of any type use ATP energy as their main energy source. ATP is also used for movement of the cell. Some early cells only used a pathway called glycolysis to make ATP energy and some of these fermented things like sugars. Later cells used photosynthesis, while more advanced cells use oxygen in the oxidative phosphorylation pathway that makes the most ATP energy. These pathways altered the atmosphere of the earth. Glycolysis and fermentation do not require oxygen so these pathways were present in cells when there was little oxygen in the atmosphere. Photosynthesis was the next evolutionary step, which uses energy gotten from the sun. The first photosynthetic cells came about 3 billion years ago. Probably, hydrogen sulfide and CO2 were used in these early cells. Using H2O or water did not come until there was plenty of water on earth. When oxygen became prevalent, oxidative metabolism evolved. This makes use of oxygen to make ATP energy, with water and CO2 as end-products. This process is much more efficient in oxidative phosphorylation than it is in glycolysis, which gave these organisms an evolutionary advantage over glycolytic cells. There are two types of prokaryotes in present time. The first is archaebacteria or Archaea and the second is eubacteria or just bacteria. Archaea are known for their extreme environments but it doesn t have to be the case. Thermoacidophiles live in certain hot sulfur springs that are acidic and hot. Some are also human pathogens.

Bacteria can be of several different shapes with small to larger genomes, depending on the organism. Cyanobacteria participate in photosynthesis as their major feature. Most bacteria are not human pathogens; however, there are some that are always pathogenic in nature. Eukaryotes have ribosomes and a plasma membrane like prokaryotes but all parts of eukaryotes are considered more complex than the same parts seen in prokaryotes. Eukaryotes are larger than prokaryotes and they are largely more interesting than prokaryotic cells. Figure 8 shows what a eukaryotic cell looks like:

Figure 8.

Eukaryotic cells are compartmentalized, which isn t as much the case in prokaryotic cells. We will talk more about eukaryotic cell evolution in the next chapter but, for now you should know that the chloroplasts and mitochondria have interesting origins from an evolutionary perspective. Mitochondria are where much of the ATP is made, while chloroplasts are responsible for photosynthesis. Lysosomes and peroxisomes are present in the cell in order to break down and digest other molecules. Plant cells contain vacuoles that have a variety of functions for the cell. Eukarytoic cells also have a cytoskeleton that helps to give the cell its structure and that helps to organize the different organelles so they stay in place. Some parts of the cytoskeleton are involved in cell movement. Eukaryotes were first on earth about 2.7 billion years ago, which is more than a billion years after prokaryotes. It was once thought that Archaea and Eubacteria were very similar but DNA analysis has shown they are actually very different. Some early evolutionary event must have happened to separate these lines of descent. Archaea are actually more similar to eukaryotes than eubacteria are related to eukaryotes. This indicates that the ancestors of archaea and eukaryotes were probably more similar to these cells than they were to bacteria. We will talk more about how multicellular organisms evolved in a later chapter. Many eukaryotic cells are unicellular but some are more complex than others. Yeast organisms, for example, are more complex than bacteria and contain more DNA per cell. Some unicellular eukaryotes have pseudopodia or false feet”, such as amoeba, which help them move from one place to another. Multicellularity developed about 1.7 billion years ago. Cells of algae for example will form multicellular colonies and will share resources. These are precursors to actual multicellular organisms. Ultimately, cellular specialization and division of labor took place in order to make what are complex organisms today. Many multicellular organisms have highly specialized cells that do many different things. Animal cells tend to have more complexity than plant cells.

KEY TAKEAWAYS •

The earth is about 4.5 billion years old. It coalesced from space dust, debris, and hot gases.

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The moon was once a pro-planet that collided into the earth billions of years ago.

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The first earth conditions were volcanic, hot, and without oxygen.

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The first organisms were prokaryotic and survived through glycolysis by taking up nutrients from the environment.

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Glycolysis developed first, then photosynthesis, and then oxidative phosphorylation.

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Viruses are ancient and mutate to a greater degree than cellular organisms.

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Eukaryotes are more advanced than prokaryotes and have membrane-bound organelles.

QUIZ 1. What was the first geological period on earth called? a. Cenozoic b. Hadean c. Paleozoic d. Phanerozoic Answer: b. The Hadean period is the first period known on earth. This was followed by several other periods. 2. During which geologic eon did mankind and mammals first occur on earth? a. Paleozoic b. Archean c. Cenozoic d. Mesozoic Answer: c. The Cenozoic eon was the latest eon. It was when mammals and mankind was first developed and happened after the dinosaurs died out. 3. When did the first prokaryotes first emerge on earth? a. Archean era b. Phanerozoic era c. Cenozoic era d. Hadean era Answer: a. The Archean era or eon is when the first prokaryotic forms of life developed on earth. This was shortly after earth s crust was solidified and when earth was no longer molten.

4. How did the moon form around the earth? a. It was once an asteroid. b. It formed from dust and gases around the earth. c. It was a small planet that crashed into the earth. d. It was broken off from the earth when it formed. Answer: c. The moon was once a small planet that crashed into the earth. The name of the planet, which was about the size of Mars, was Theia. 5. What type of organism make up stromatolites, which are the earliest evidence of life on earth? a. Sulfur-producing bacteria b. Algae c. Fungi d. Cyanobacteria Answer: d. Cyanobacteria made up stromatolites, which are the earliest evidence of life on earth. These were found in Greenland that dated back to 3.7 billion years ago. 6. What does the fossil record show of life in the Hadean period of earth’s existence? a. There were no fossils during his period of time. b. Cyanobacteria existed in rock fossils. c. Algae existed in ocean fossils. d. Biofilms have been found in the fossil record. Answer: a. There were no fossil records during this period of time but there has been graphite found to be imbedded in certain rocks, which indicate the possibility of life.

7. What is the theory of virus evolution that indicates that viruses were once small, cellular parasites that evolved into viral particles? a. Escape theory b. Virus first theory c. Degeneracy theory d. Coevolution theory Answer: c. The degeneracy theory is that viruses were once intracellular parasites that evolved into virus particles, which would be somewhat of a de-evolutionary process. 8. What is not true of virus mutations? a. RNA viruses mutate faster than DNA viruses. b. Antigenic drift happens when mutations accrue over time. c. Genetic shift happens when viruses shuffle their genes. d. Viruses can mutate but do not infect more than one species. Answer: d. Viruses can mutate so that they can infect more than one species of organism. Each of the other statements is true. 9. Which type of prokaryote is known for its ability to survive in extreme temperatures? a. Archaea b. Eubacteria c. Cyanobacteria d. Intracellular bacteria Answer: a. Archaea are especially known for their ability to survive in extreme environments of all types, including extremes of pH and temperature extremes.

10. What is not a function of the eukaryotic cell’s cytoskeleton? a. Movement b. Preventing cell desiccation c. Organizing organelles d. Maintaining cell structures Answer: b. The cytoskeleton does each of these things but it does not involve itself in cell desiccation protection.

Chapter Six: Major Life Transitions There is more to be said about evolution than the evolution of single-celled organisms so this is the topic of this chapter. Eukaryotes are infinitely more complex than prokaryotes—even those that are unicellular. Many eukaryotic organisms are multicellular; for this reason, the evolution of multicellularity is discussed in this chapter. Because evolution happens to populations rather than to individuals, it is important to also talk about the evolution of individuality. There are advantages to evolving in a social environment, which is also covered in this chapter.

ORIGIN OF EUKARYOTES As you remember, the eukaryotic organisms, also called Eukarya or Eukaryota, are one of three domains of life that also include Bacteria and Archaea. Most of the life that can be seen without a microscope represents eukaryotic cells. Plants and animals are both eukaryotic. These are more complex, have linear strands of DNA, have DNA within a nucleus, and have membranebound organelles. Most plants are characterized by the presence of chloroplasts. Chloroplasts are entirely used for photosynthesis. Plants still have mitochondria for energy production but need chloroplasts to capture light energy in order to make complex organic nutrients. Both plants and animal cells have mitochondria in the cells. Mitochondria are double-walled organelles that make the majority of the ATP necessary for cellular energy. The processes involved in oxidative phosphorylation take place within the mitochondria. Figure 9 shows the structure of a typical mitochondrion:

Figure 9.

Eukaryotic cells are likely the descendants of symbiotic prokaryotic cells that were once separate cells. It is believed that mitochondria were once separate prokaryotic cells that were taken up by larger prokaryotic cells. They may have been engulfed by the larger cell types but remained as symbiotic partners to create eukaryotic cells. This type of symbiosis is called endosymbiosis. The evidence for endosymbiosis, including the following: 1) There are double membranes in both mitochondria and chloroplasts. No other organelles have a double membrane. 2) Mitochondria and chloroplasts have their own DNA, which happens to be circular. This is passed in humans from mother to child because only egg cells bring their mitochondria with them. 3) Mitochondria divide through binary fission or by pinching into two halves, which is how this is done with bacteria. Chloroplasts are similar to mitochondria but, because of the way that evolution works, mitochondria likely were endosymbiotic in eukaryotes first and chloroplasts did this second. This is because all eukaryotes have mitochondria but only plant cells have chloroplasts. Neither chloroplasts nor mitochondria can live independently because the necessary proteins to make and operate them are found in the host genome and not in the mitochondrial or chloroplast genome.

EVOLUTION OF MULTICELLULARITY Multicellular organisms consist of more than one type of cell. The cells are dependent on one another, which is not always the case with unicellular organisms. We talked about algae, which are considered multicellular. Things like slime molds and social amoebae are intermediaries between being a unicellular organism and a multicellular organism. There is such a thing as pluricellular organisms”, which are colonial organisms rather than truly multicellular. Multicellularity did not happen in a single independent time in evolutionary history but instead evolved at least twenty-five separate times. It has occurred in eukaryotes and some prokaryotes, such as myxobacteria, cyanobacteria, and actinomycetes. It has only stuck throughout evolution in six instances, including brown, red, and green algae, fungi, animals, and land plants. The first sign of this phenomenon in evolution was 3 to 3.5 billion years ago among organisms similar to cyanobacteria. A necessity for multicellularity to become possible is that the organism must be able to reproduce itself in order to make an entire organism. This means being able to have differentiation into sperm and egg cells, also called germ cells”, for the purposes of reproduction. In addition, there should be the ability to differentiate into different types of nonreproductive cells. There are more than 100 different types of cells in animals and about 10 to 20 different types of cells in fungi and plants. Finally, cells should have the ability to adhere to one another if multicellularity is to be possible. Some organisms have been found to have lost their multicellularity as part of their evolutionary process. Certain fungi have reverted to become unicellular after a period of time being multicellular. This has also happened in some algae. It is believed that these organisms simply reverted to their previous unicellular state. Other organisms have reduced their multicellularity due to losses in the number of different types of cells. This has occurred in certain protozoa. Multicellular organisms carry the risk of developing cancer, particularly in those that live long. Cancer can happen in plants and animals. When this happens, some believe this represents a loss of the organism s multicellularity because it involves a loss of differentiation of the cell. So, how did multicellularity develop? Some believe that there were cells that aggregated into a grex, which is a slug-like mass, and that this functioned as a multicellular organism. Slime molds behave this way. Others believe that nuclear division occurred at one point without formation of a separating cell membrane in order to form a coenocyte that functioned as a multinucleated cell. This would have led to a functional, multicellular organism. Still others

believe that cells divided but did not separate from one another. This is what happens in embryos. The early multicellular organisms did not leave a good fossil record because they weren t bony nor did they have hard body parts. Demosponges, however, did leave behind fossils and were early multicellular organisms. There are other early multicellular organisms that did yield a fossil. For this and other reasons, it has been hard to find ancestors of most multicellular organisms. What we do know comes mainly from studying the development of embryos. There are theories as to how multicellularity evolved. One theory is the symbiosis theory. This suggests that it started with cooperation or symbiosis of different single-celled organisms that later became dependent on each other. This theory would involve an exchange in DNA eventually in order to create a new species. Clown fish and sea anemones are extremely codependent on one another, for example. The problem with this theory is that it isn t known how the DNA would be exchanged. The only time this is known to have occurred is when chloroplasts and mitochondria were involved in endosymbiosis. Another theory is called the syncytial theory or cellularization theory, which involves a cell with multiple nuclei. Support of this theory is seen with slime molds and ciliates. This, however, doesn t completely explain multicellularity. This is because, in organisms that have more than one nucleus, there is usually one large macronucleus and smaller micronuclei used for sexual reproduction. A third theory is the colonial theory is that organisms of the same species developed symbiosis among themselves. This is seen in some land-evolved organisms but not in aquatically-evolved organisms. This phenomenon is seen in certain protists, such as amoeba. These are called colonial protists. The combined groups of organisms will function as one organism but this probably indicates pluricellularity rather than multicellularity. There are advantages to multicellularity. It allows organisms to be bigger than could be explained by diffusion alone. This allows for a certain competitive advantage to these types of organisms. Multicellular organisms also live longer than unicellular organisms because it allows some cells to die with others surviving. Despite these apparent advantages, unicellular organisms are more successful in the environment than animals but they are not more successful than plants.

EVOLUTION OF INDIVIDUALITY As you have seen, there has been a shift in evolution toward greater complexity, particularly in multicellular organisms. The truth, however, is that this has not happened in all evolutionary lines and many organisms are still unicellular. Evolution has not actually been completely gradual. It has happened through a small number of major evolutionary transitions. Much of these transitions have involved the cooperation of different cells and organisms to form an entity that is more complex than prior entities. One of the major transitions that has occurred is in the way DNA and other heritable information is stored and passed on to create progeny individuals. This involved organisms that were once able to replicate by themselves but later could only replicate as a group. It also involved a lack of conflict between the different cells that have come together so they can work toward the same goal. How does this work? There is more than one step to this process. It takes first the formation of a more cooperative collection of organisms. It then takes cohesiveness within the group so it can be seen as a single organism. Lastly, it takes some type of division of labor within the group. There are questions one must ask about how this transition occurs. For example, what conditions favor things like cooperative group formation, cooperation between the cells, division of labor, communication between the cells, and a reduction in conflict within the organism? There needs to be some benefit to the cooperative process that directly affects those that cooperate versus those that do not cooperate. Some benefits include evasion of predators, the ability to make fruiting bodies that help in dispersal of young, and increased efficiency in the use of factors that individual cells secrete. There is a phenomenon in evolution called kin selection. It means behaviors of one cell or organism that directly or indirectly benefits the organism that has the same DNA as the organism doing the behavior even if it does not directly benefit the individual itself. Bees do this type of behavior because there are many worker bees that ensure the survival of the species even if it doesn t ensure the survival of the worker bees. Cooperation can be directed at nonrelatives if it also benefits the cooperator. This is seen in ant colonies who benefit from each other. There are certain conditions that favor the division of labor among the parts of an organism. Division of labor can be seen in certain algae that make small cells whose job it is to keep the colony floating because the cells make flagella for this purpose. Another case is seen in

cyanobacteria that divide into nitrogen fixers and photosynthetic cells. In these cases, the division of labor favors the organism. All symbiotic relationships involve division of labor. Anytime that division of labor is more efficient, this will be the favored relationship. Cells that have aggregated need to communicate with one another. One of the things that can complicate this is that there can be cheaters” that signal dishonestly or that don t respond to signaling efforts. This means that the communication must be honest. Signaling mechanisms cannot be easily faked and must be costly to fake. Both the sender and receiver must share common interests. There also must be minimal conflict between the different cells in a group. The goal of cooperation and minimal conflict is maximization of the fitness of the entire group. In the case of workers in a cooperative, conflict can be avoided if the helping worker is just as related to another worker s offspring as if it had the offspring itself. In other cases, competition is repressed, as is seen in some bee colonies where workers destroy the eggs laid by other workers. In some cases, a cooperative group can break up but the individuals can still reproduce. This would not be an advantage that favors mutual dependence. Mitochondria, for example, cannot reproduce by itself if separated from the cell. Termite queens can t reproduce if the workers don t cooperate. The thing that most favors mutual dependence is extreme division of labor. Exactly how this occurs isn t known.

TRANSITION TO GROUP LIVING What about organisms—plants, animals, or others—who live in a group setting? Why do they do this and why to animals help each other out when it is costly to their own survival? Some animals are inherently asocial. These include polar bears and mosquitoes. Others are very social. These include wolves, who live in packs, and fish, who live in schools. Ants, bees, wasps, and termites are the most social of all animals because they live in tightly woven colonies. Social behavior can be very adaptive, meaning that increases the fitness of the parts, usually through improved reproductive success. Social behavior can provide protection against predators. Think about bird flocks, schools of fish, and herds of wildebeests, which can escape predators by living in groups. It basically decreases the odds of any one organism getting killed by a predator. There are risks and benefits to forming social groups. One of the benefits happens when one organism does something to aid another. This is called altruism. With altruism, there is some

cost to the organism providing the help or at least there is a potential cost. This happens in squirrels, when one squirrel cries out to warn others about a predator. Sharing nesting space and raising another s young are also examples of altruism. There is an individual cost but an overall advantage to the group. When a group of vampire bats, for example, involve those that get food and those that don t after a hunting expedition, those that get food share it with those that don t. This is an example of both altruism and reciprocity. Reciprocity means that, on another expedition, the one who previously gave food to others will, at another time, be the receivers of food. Bats who don t share are less likely to get fed at a later date. Because of kin selection, the same bats are more likely to share with relatives than with nonrelatives. This allows researchers to see the relatedness of different bats in a group. The advantage to kin selection is that there is an increased chance of the donor s DNA getting passed from one generation to another. Eusocial animals are those that live in colonies. In these types of colonies, only a few of the members have the opportunity to reproduce. These include the naked mole rate, certain reefdwelling shrimp, termites, ants, some bees and some wasps. It is a feature of these colonies that they usually produce large numbers of offspring and the benefit is greater than it would be if the individuals had the opportunity to reproduce themselves. There are often large structures for these organisms, which is where they live. These colonies are well-defended and tend to do very well.

KEY TAKEAWAYS •

Eukaryotes are unique in that they have mitochondria and/or chloroplasts that have been introduced to the species through endosymbiosis.

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There are advantages to multicellular organisms but a major feature is that high specialization means that one cell cannot break off and reproduce itself.

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There are things that favor the formation of an individual organism from multiple separate parts.

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Kin selection involves giving special favors to another individual in a group because they are related to them.

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Altruism is when one member of a group gives to another, even if there is a cost to the giver.

QUIZ 1. Which organelle in a eukaryotic cell is responsible for photosynthetic processes? a. Chloroplasts b. Mitochondria c. Nucleus d. Endoplasmic reticulum Answer: a. Chloroplasts contain the apparatus necessary for the capture of sunlight to make organic molecules through the process of photosynthesis. 2. Which organelle in a eukaryotic cell is responsible for making ATP energy to the greatest degree? a. Golgi apparatus b. Nucleolus c. Mitochondria d. Endoplasmic reticulum Answer: c. Mitochondria participate in several cellular processes that make ATP energy for eukaryotic cells. ATP can be made in other parts of the cell but mitochondria make the most ATP than other parts of the cell. 3. What organism is considered an intermediary between unicellular and multicellular organisms? a. Slime molds b. Algae c. Mushrooms d. Bacteria

Answer: a. Each of these represents a single-celled or multi-cellular organism, except that slime molds are considered intermediaries between the two types of organisms. 4. What is another name for colonial organisms, as is seen in some protists? a. Multicellular b. Biofilms c. Unicellular aggregates d. Pluricellular Answer: d. Colonial organisms are considered pluricellular because they contain many cells but do not actually qualify as being multicellular organisms. 5. What is not a theory on how multicellularity occurred in the evolutionary process? a. Cells that were identical formed a conglomerate that functioned as a single organism. b. A cell divided its nucleus but did not have a dividing cell membrane to make a coenocyte. c. Cells divided but did not physically separate. d. Cells of different organisms came together to function as a single unit. Answer: d. Each of these is a theory of how multicellularity occurred except that it is probably not possible for cells of different organisms to come together as a functional multicellular unit. This would involve two different genomes coming together, which does not happen.

6. What is the main way that the evolutionary relationships between multicellular organisms is studied? a. By looking at embryological development b. By studying the fossil record c. By examining DNA sequences of modern organisms and ancient organisms d. By looking at the morphology differences between modern organisms and their ancestors Answer: a. Because the DNA of ancient organisms cannot be studied and older microorganisms did not leave behind a fossil record, most of the research is studied by looking at embryological development. Sometimes, biochemical differences between organisms are also used to look at an organism s phylogeny. 7. The phenomenon where an organism does things that benefits its close relatives is called what? a. Parasitism b. Mutualism c. Symbiosis d. Kin selection Answer: d. Kin selection involves the behaviors done by certain organisms that directly or indirectly benefit their close relatives. The more related the organism is, the greater is the benefit to it by the behavior.

8. What is the greatest advantage to the division of labor in an organism that is multicellular? a. Increased ability to avoid predation b. Larger size of the organism c. Greater efficiency of the organism d. Greater mobility of the organism Answer: c. The greatest advantage in the division of labor in an organism that is multicellular is a greater efficiency of the organism if some cells do one thing and other cells do other things. 9. What is not an example of altruism in a group of animals? a. Sharing nesting space with others b. Raising another animal’s young c. Cooperating to get food for the group d. Warning others of danger Answer: c. Each of these is an example of altruism except for cooperating to get food for the group. Part of the definition of altruism is that there must be a risk or potential risk to the one giving the help. 10. Under which situation will altruism be more likely to occur between organisms of a group? a. There is a greater benefit to the recipient of the altruistic act. b. There is increased relatedness between group members. c. There is less relatedness between the group members. d. There is greater cost to the giver of the altruistic act Answer: b. Altruism tends to be the greatest if there is increased relatedness between the group members. This is because it maximizes the chance of passing on the DNA of the giver and receiver of the altruistic act.

CHAPTER SEVEN: SPECIES AND SPECIATION The major topics of this chapter are species and speciation. Earlier chapters talked about evolution and its role in the diversity of species on earth. In this chapter, we talk about how species are defined and the different methods in which speciation or the formation of a different species occurs. Historically, species were defined by their similar characteristics but, in this chapter, we talk also about how the knowledge of genetics has changed the definition of what exactly is meant when referring to an organism being of a certain species in today s scientific terms.

IDENTIFYING SPECIES As we have already discussed, an organism s species is the smallest and most basic unit of classification in taxonomy. There are several ways to identify a species. You can call a species a group of organisms that have the ability to produce fertile offspring. You can also look at things like DNA sequence or karyotype, behavior, morphology, or ecological niche. While it may seem simple to identify a species using these methods, issues like hybridization can get in the way of actually determining what the species of a given organism falls under. Reproductive status cannot be used in identifying asexually reproducing organisms. In addition, because evolution is not just a thing of the past, there are things that can cause a species to change in present time. At the end of this chapter, we will talk about how genetics are increasingly being used to quantify a species. Back in Darwin s day and, in fact, not too long ago, species were identified by morphology. Some researchers looked more at what can be defined as species concepts rather than species themselves. John Wilkins, for example, identified several species concept groups. These include the following: •

Recognizing agamospecies as being those that reproduce asexually

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Using the term biospecies to identify those that are reproductively isolated

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Ecospecies defines those that have certain ecological niches

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Using evolutionary species to define those that have the same lineage

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Genospecies or genetic species defines those with the same gene pool

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Morphospecies are those that have a specific phenotype

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Taxonomic species are those that can be defined using taxonomic principles

The term morphospecies is also referred to as a typological species. This is a group of organisms that each have specific characteristics or properties that can easily be determined just by looking at the organism. This was the classical method of defining the species, used in Linnaeus s time. The problem is that you can have slightly different characteristics in organisms of the same species that do not necessarily mean they are of an altogether different species type. The term mate-recognition species is used to identify those organisms that have the ability to recognize one another as possible mates. This is similar to cohesion species, which is a group of organisms that have the ability to have phenotypic cohesion, regardless of whether or not they can make hybrids when they reproduce. Because bacteria can transfer their DNA to other distantly related bacteria, they represent a particular problem. This has led to the concept of DNA barcoding. This is an aspect of mitochondrial DNA within a gene that codes for cytochrome c oxidase. This has been sequenced for nearly 200,000 species and can be used to identify what species an organism belongs to. An organism s evolutionary species is also called their phylogenetic or cladistic species. This looks at the common ancestors of a given organism type. This is best done by looking at DNA sequences of a group of organisms that have similar proteins to see when they last diverged from one another. The advantage of this is that it doesn t involve reproductive capabilities so it works for asexual organisms. Sometimes, more than one area of DNA needs to be looked at, although it can unnecessarily make more species out of a group than there really are. Because it is really difficult to study extinct species, paleontologists use the term Chronospecies to define a single lineage or organisms that have changed their morphology over time. This allows the researcher to make a distinction as to when an organism has changed so much that it has in fact become its own species. It is even more difficult to define the species of a virus particle because the population is so big and changes greatly over short periods of time. Viruses are not said to have an exact species name but are instead referred to as having a quasispecies. Quasispecies are not the same thing as the species of a virus because, as non-living entities, they do not have a species name.

Species are discovered and given their taxonomic name when they are identified and their characteristics published in a publication that assigns it a specific and unique scientific name. The organism itself is kept in a museum or university collection so they can be verified as new and to compare the different specimens. The person who defines a new species gets to name it but they must use an appropriate name, according to the International Code of Zoological Nomenclature. There are other resources that keep track of the different species. All of these varying issues related to the definition of species has led to what is known as the species problem”, which highlights the fact that there are many definitions of species—none of which is completely satisfactory. There are differences between species definitions, such as morphospecies and molecular-based definitions of species that lead to discordant results in some cases. As mentioned, horizontal gene transfer represents perhaps the major stumbling block to determining the different prokaryotic species as well as some eukaryotic species. There are also what are called species aggregates or microspecies, usually seen in plants. These are groups of related organisms that are complicated by things like polyploidy, hybridization, and apomixis, which is the replacement of sexual reproduction with asexual reproduction. Insects, treefrogs, and fungi also have microspecies aggregates. Fertile hybrids lead to gene flow between more than one population of organisms; their presence challenges the idea of reproductive isolation as a way of determining a species. Certain species of crows can form a hybrid bird if they are in the same geographical area. Ring species involves a series of different species that do not share the same geographical area but that can interbreed in those areas where the ecological niches are overlapping. This leads to potential for gene flow between the different species but only in those that are close to one another geographically. The phenomenon of ring species is not common. Salamanders in the US, warblers in Asia, and certain gull species are ringed species.

SPECIATION AND MODES OF SPECIATION Speciation is defined as the evolutionary processes that take place in order to lead to the development of a new species. Charles Darwin said that natural selection was the major cause of speciation and that sexual selection was the main mechanism for this. Later terms related to this were cladogenesis, which is the splitting of lineages into two more descendent lineages, and anagenesis, which is phyletic evolution within a given lineage of organisms. Darwin himself asked why species exist at all. He wondered why, because there are fine distinctions between related organisms, there aren t an infinite number of transitional forms of an organism. Why aren t species easily defined, he asked. He also wondered why there weren t more transitional species occurring over time. He determined that there was something about natural selection that both generated and maintained the different species. One of the issues related to this is the fact that, if there was out-crossing sexual reproduction, which is interbreeding between species, the cost would be that there would be many different species, each of which would be rare and have few members. It would be too difficult to find a mate. Species with higher numbers would increase in number because they would have more sexual mates, while species with lower numbers would be driven quickly to extinction. In addition to reproductive costs, rarity of an organism is costly because their rare features are generally not an advantage to the organism. This leads to species members avoiding mates that have rare features—a phenomenon called koinophilia. This further leads to the reproductive isolation and uniformity of the species. There are four different modes of speciation that each have taken place in the evolutionary process. These are allopatric, parapatric, peripatric, and sympatric modes of speciation. With allopatric speciation, species are created by things like habitat fragmentation that alter the geography of a species. There are dissimilar selective pressures to the different groups, antigenic drift, and the presence of different mutations. Should they come into contact again, the differences that have occurred make them reproductively isolated from one another. This is what happens with island evolution, where organisms are isolated on a small island. Peripatric speciation, a population gets isolated and forms its own species. This is a subtype of allopatric speciation and is related to the founder effect, in which just a few organisms found” a new population. Genetic drift plays a major role in this phenomenon.

Parapatric speciation involves the partial separation of geography between species. There is cross-breeding but reduced fitness of the heterozygous organism that prevents interbreeding. This speciation occurs because of differences in ecological niches in nearby populations of organisms. Sympatric speciation involves a single ancestor in the same geographic location that forms different descendent species. It can happen when insects become dependent on different types of host plants in the same geographical area. Ecological factors also play a role in this type of speciation. The Wallace effect is also referred to as reinforcement. This happens when natural selection reinforces or increases the reproductive isolation of a species. It is sometimes seen when separated populations come together again. If they haven t developed into completely separate species, the organisms can interbreed to produce hybrids that might not be fertile themselves. If they are infertile or subfertile, the reproductive isolation will increase and species formation will happen. This is what happens in the making of mules from horses and donkeys. If the hybrids are more fit, species separation will not occur. Ecological selection involves the interaction between the organisms and their environment, particularly when it comes to acquiring resources. Ecological niches play a role in all forms of speciation because they exert different pressures on the organisms living in them. Can new species be formed artificially? It has been used in many instances of animal husbandry. In some cases, the wild animal that led to the domesticated animal can interbreed with each other. It has been done in the laboratory with fruit flies, which were gradually differentiated into separate species through differences in habitat selection. They can also be isolated by differences in nutrient preferences. Anytime a different ecological pressure is exerted on an organism, the tendency toward speciation occurs. Speciation is possible if polyploidy happens. If there is failure of meiosis to make diploid gametes, the end result is an offspring that has more genes in it than either parent. It causes rapid speciation, even though it sometimes yields sterile offspring. This occurs particularly in plants but it has probably occurred in animals over the course of evolutionary history. Some of these polyploid offspring are able to reproduce asexually. Sometimes, hybridization between two distinct species causes a new phenotype to appear. If it is fitter than the parents, this phenotype will be selected for. It will become a new species if reproductive isolation happens as well. Because reproductive isolation is difficult to achieve,

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this type of speciation does not happen very often. Hybridization without polyploidy is more uncommon than that which happens with polyploidy. No one knows exactly how fast speciation occurs over time. Some believe there is phyletic gradualism, which means there is a slow but gradual change in species. Punctuated evolution involves more rapid evolution, which is seen with domestication and plant manipulation by growers. Corn, for example, has rapidly evolved over a short period of time. This leads some to wonder why actual natural evolution takes so long. The fossil record supports punctuated evolution, with the sudden appearance of certain organisms occurring in the fossils seen by paleontologists.

GENETICS OF SPECIATION Charles Darwin had a difficult time defining what a species was. Since then, many different ways of defining species have been developed so that there are more than 70 different definitions of species used to define any new ones. What this means is that species as a concept is largely a manmade idea. Nowadays, genetics is increasingly applied to defining a species. According to recent research, a new species can be defined if just 2 percent of their DNA is unique to the organism. One of the difficulties of using genetics to define a species is that it tends to increase the number of species than can be defined with using morphology alone. These techniques can identify what are called cryptic species”, which look identical to other species but are actually genetically different. Mayr s concept of reproductive isolation has rapidly fallen apart. One advantage of using genetics to define a species is that it is better at identifying endangered species that can get the protection they need under laws like the US Endangered Species Act. Without genetics, the identification of endangered species becomes almost impossible. A disadvantage is that it is a more expensive way of defining a species.

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KEY TAKEAWAYS •

There are many different definitions used to identify the different species.

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There are four modes of speciation with ecological niches factoring in each of these modes.

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Mayr’s species definition mainly defined species as having reproductive isolation.

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Genetic speciation is expensive but defines cryptic species that look the same as other species but are genetically different.

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QUIZ 1. What is the least effective way of determining that an organism is in a specific species? a. Morphology b. Fossil record c. DNA sequence d. Reproductive status Answer: b. Species are not generally looked at in terms of their fossil record, although some paleontologists use this as a last resort to identify an extinct species. 2. A species concept that is used specifically to define a species that reproduces asexually refers to what type of species? a. Genospecies b. Morphospecies c. Agamospecies d. Biospecies Answer: c. The term agamospecies defines those that can be defined without reference to sexual reproduction because these species reproduce asexually. 3. What term is used by paleontologists to look at species that have changed their morphology over the course of evolution rather than changed into a different species? a. Genospecies b. Quasispecies c. Chronospecies d. Ecospecies

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Answer: c. The term Chronospecies is used to define a species that may have changed over the course of time in the evolutionary process but is still the same species. 4. What type of organism has a quasispecies rather than an actual species? a. Plant b. Archaea c. Bacteria d. Virus Answer: d. Viruses are not living organisms so they do not have a species name. Instead, they are referred to as having a type of quasispecies organization pattern. 5. What is it called when an ancestor species breaks off into two or more distinct descendants? a. Ringed species hybridization b. Horizontal gene transfer c. Anagenesis d. Cladogenesis Answer: d. Cladogenesis is an evolutionary process that has an ancestor organism splitting into two or more separate species along evolutionary lineages. 6. What was Darwin’s major dilemma when he asked why species existed in the first place? a. Why there weren’t an infinite number of transitional forms between species. b. Why species become extinct over time. c. Why organisms of the same species can look different. d. Why geography seems to support the development of different species. Answer: a. His major dilemma was why there weren t an infinite number of transitional forms between the species, either in a certain

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geographical area or over a period of time in the evolutionary process. He assumed there was a reason that natural selection favored speciation. 7. Which mode of speciation happens when a few founders of a new colony break off from the main colony, with the effect of starting a small group of new species members? a. Allopatric b. Peripatric c. Parapatric d. Sympatric Answer: b. Which peripatric speciation, a few organisms separate from the main group in order to have a new species develop with just a few founders. 8. According to the Wallace effect, how does the reinforcement of species separation happen? a. The organisms operate in different ecological niches b. One organism is a predator to another organism c. The hybrid organism is infertile or subfertile d. The hybrid has increased fitness than either of the separate species Answer: c. If there are two related species and the hybrid of these is subfertile or infertile, there will be the reinforcement of the species, according to the Wallace effect. 9. What type of evolution is favored by the fossil record and by animal husbandry? a. Phyletic gradualism b. Stable species after they have developed c. Punctuated evolution d. Frequent mass extinction with rebirth of new species

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Answer: c. Punctuated evolution is rapid evolution over a short period of time, which occurs in the fossil record when new species suddenly appear and when animals or plants are quickly speciated artificially over very short periods of time. 10. How much different can the DNA of an organism be unique as a minimum in order to call it a new species? a. 2 percent b. 16 percent c. 40 percent d. 65 percent Answer: a. At a minimum, two percent uniqueness in an organism s DNA can be enough to call a species as being different from another.

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CHAPTER EIGHT: EVOLUTION OF THE HUMAN SPECIES This chapter talks about the evolution of the human species. From an evolutionary perspective, humans have not been around very long. Even so, there have been many changes that have taken place over the course of about 400,000 years. As you will see in the chapter, there have been changes in brain size and gait, among other things, that have been a part of the processes necessary to turn ancient species into modern man.

EARLY MAN Early man can also be referred to as archaic humans. Modern humans arrived on earth about 315 thousand years ago. Our modern species is called Homo sapiens. Early humans have been referred to in differing ways. Homo neanderthalensis or Neanderthal man first evolved on earth at around 430 thousand years ago. Other ancient humans include the Denisovans, Homo rhodesiensis, and Homo heidelbergensis. Figure 10 describes human evolution:

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Figure 10.

The three things that most differentiate archaic man from modern man are prominent brow ridges, thick skulls, and lack of a prominent chin. Their head size was relatively close to that of modern man and they walked upright. Actual modern humans” first appeared in Ethiopia about 160,000 years ago; they gradually replaced the archaic humans, although non-modern humans may have coexisted with man as recently as 12 to 30 thousand years ago. There is no clear-cut definition of what archaic humans really were. Some include all archaic forms of human life under the category of Homo sapiens, with the archaic species being subspecies. This leads to a three-part name, such as Homo sapiens neanderthalensis, rather than Homo neanderthalensis. Others use the term Homo erectus to define archaic humans. Problematic is the fact that some early modern species of man had archaic features.

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The evolution of archaic humans was likely some type of punctuated equilibrium. Remember that this means the evolution happened relatively quickly over a short period of time. Brain size increased from about 900 milliliters in Homo erectus to about 1300 milliliters. It reached a peak and has since started to decline in modern mankind. Archaic humans most likely used language for the first time. This is based on what we know of the brain size in these humans and the fact that they likely lived in larger groups. It is argued that, if humans lived in large groups, they must have had language in order to stay together.

HUMAN EVOLUTION Human evolution started with the first evolutionary strides of primates. There are several terms used to describe human evolution you should know about in order to understand how humans have evolved: 1. Hominoid—this defines an ape, which also includes the gibbons and the hominids in general. 2. Hominid—this defines the great apes, including gorillas, orangutans, chimpanzees, and humans. 3. Hominine—this defines the subfamily that includes gorillas, humans, and chimpanzees, but doesn’t include orangutans. 4. Hominin—this defines the Hominini tribe, which includes chimpanzees and humans. 5. Homininan—this includes humans and their ancestral relatives but doesn’t include chimpanzees 6. Human—this defines only Homo sapiens, of which modern humans are the only extant species. The process of human evolution requires the development of language and bipedalism. This was never a linear ascension but was more web-like because it involved a great deal of interbreeding with archaic human forms until there was the ascension of modern man. Everyone has a small number of Neanderthal genes in their DNA. In terms of relatedness, the first separation away from other great apes occurred with the gibbon family about 15 to 20 million years ago. Next, there was the divergence from the orangutan family about 14 million years ago. Then came the breakoff from the gorilla family about 8

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million years ago. Finally, about 4 to 7 million years ago, humans parted from chimpanzees, which are our closest modern relative.

HUMAN STRUCTURAL CHANGES There have been several changes that have occurred throughout evolution to lead to modern man. Bipedalism was the key evolutionary adaptation that led to major skeletal changes. The first bipedal species was Sahelanthropus or Orrorin, which both arose about 6 million years ago. These were believed to have primitive forms of bipedalism. The genus Ardipithecus was fully bipedal around 5.6 million years ago. What was the value of bipedalism? Some believe that it better enabled long distance running, enhanced our field of vision, kept the hands free for tools and food carrying, and avoided hyperthermia through decreased sun exposure on the back. It uses less energy than quadrupedal walking. The arms shortened and the legs lengthened over time and the big toe began to be lost as a grasping object. The main changes to the skeletal system was to the legs and pelvis. Other changes involved those to the vertebral column, which gained a new shape, change in alignment of the big toe so it would help in moving forward, and shortening of the arms for easier running. The pelvis changed the most, with the disadvantage of narrowing the birth passage. This has made the birth process more difficult and more complex, and limited the brain size. It shortened the gestation time and made human babies ambulatory at a later age. Menopause evolved and the menstrual cycle changed so that it led to the advantage of women to help raise their grandchildren rather than continue to raise their own children. Girls arrive at menarche at a later age. The human brain is greater than that of other primates. Humans have about a 1330-milliliter brain size, which is three times that of gorillas and chimpanzees. Ardipithecus and Australopithecus had stable and relatively small brain sizes, while greater brain size was first seen in Homo habilis. Neanderthals had the largest brain size; it has fallen since that time. Along with this has been an increase in brain growth after birth so that there could be social learning and the acquisition of language in young humans. The brain structure has changed, even as the size has decreased. The temporal lobes, responsible for language, have increased as has the prefrontal cortex, which handles decisionmaking and social behavior. There have been changes in the overall morphology of the skull,

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which have helped the brain have more growing room. The cerebellum size has also increased, which is responsible for things like balance and motor control. It may also have increased in response to the need for speech. There has been a reduced change in sexual dimorphism, which represents the differences between makes and females. The male canine tooth has shrunk in size and the brow ridge has decreased. Humans now have a hidden estrus, meaning that it can least likely be determined when they are fertile. Females are now fertile year-round. Males are still larger than females and have different degrees of body hair and a different subcutaneous fat pattern. These things were believed to increase pair bonding between men and women. The genus Homo has a unique structure associated with the opposition of the thumb and the little finger that doesn t exist in other species. This feature is said to lead to an increase in grip strength and in the ability to do skilled manipulation of the hand. Other changes include a greater dependence on vision, longer period of youth development, a smaller gut, and a greater metabolism. Body hair has been lost, the teeth positions have changed, the chin has developed, and sweat glands evolved. There have been several ways of determining the place of modern man and our relationship to older human beings. Skulls have been discovered since the middle of the 1800s to the present time, which help to determine the timeline of human evolution. Genetics has also played a role in determining relationships. Research has been done on the immunological similarities and differences between modern primates and humans. DNA sequencing has also been done on homologous or related proteins. These provided a sort of molecular clock to help fill in the blanks that can t be gotten through skeletal remain discoveries. This last technique has provided the best analysis of the divergence times of the different species. A more recent paper suggests that, even when early chimpanzees and early humans diverged in prehistory, there was interspecies mating that took place, which affected the gene pool. There were likely two splits in the lineages of these species. One related to the species divergence but included interbreeding and the other that involved a lack of interbreeding.

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HUMAN MIGRATION Mitochondrial DNA, which is only passed from mothers to their children, is used to determine the migratory patterns of early humans, which was modified by the fact that the continents were a bit more accessible to one another than they currently are. Genetics has helped the investigation of migration patterns. The genus Homo has migrated out of Africa a minimum of three separate times. The migration patterns are believed to be related to changes in the climate. Human artifacts have been found near New Delhi that date from 2.6 million years ago. This is earlier than it was once believed. Chinese archaeological digs have found human tools from about 2.5 million years ago. The area of Ethiopia in Africa is believed to be the origin of the X and Y chromosomes of the first human man and woman. Modern humans are believed to have exited Africa about 55,000 years ago, even though others left earlier than that. Genetic studies have identified Mitochondrial Eve and Y-chromosomal Adam. These were the progenitor humans that first gave rise to our modern human species. The theory is called Out of Africa”, which has also been supported by archaeological findings, such as the finding of Lucy, an example of an australopithecine from 3.2 million years ago in the 1960s in Ethiopia. There was some mixing between Neanderthals and Denisovan species and, as mentioned, all humans have Neanderthal genes—about 2 to 4 percent of the total genome. Some modern humans living near Fiji and New Guinea have Denisovan alleles as well. This does not complicate the idea that we came out of Africa but suggests it did not just happen once. Denisovan genes have been found in Tibetan populations as well. The most current dispersal theory indicates that humans dispersed along coastal regions to an area around Yemen around 70,000 years ago, populating Oceania and Southeast Asia. They were believed to use mainly marine resources. A later group traveled through the Persian Gulf to the Middle East, while some populated Eurasia. Rising sea waters likely destroyed most of the evidence of the first group of migrants. There is a single migration lineage called L3 that gave rise to all people who are not African.

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EVIDENCE FOR HUMAN EVOLUTION As with the evolution of other organisms, several fields of study are involved in how this worked over time. The fossil record was used traditionally but now genetics has largely taken its place in determining where humans came from. This study of human life and its origins is called anthropology or paleoanthropology. The extant hominoids, those currently living, are humans, bonobos, chimpanzees, gorillas, gibbons, and orangutans. As mentioned, gibbons are our most distant relative, while bonobos and chimpanzees are our closed relatives. The similarities between chimpanzees and humans indicate the sharing of between 95 and 99 percent of DNA. Speciation was very drawn-out, however, in part because of inbreeding. Mitochondrial Eve loved around 200,000 years ago in Africa. The fossil record for the divergence of gorillas, chimpanzees and hominins is lacking. The earliest fossils of the hominin type were Sahelanthropus and Orrorin genuses, which date back 7 million and 5.7 million years ago, respectively. They may or may not have been our direct ancestors but could represent another branch of apes. Australopithecus species arose about 4 million ears ago. They had descendants that were our ancestors. Lucy herself was an Australopithecus afarensis, found in Ethiopia. There are relatives of hers that were found in South Africa. Homo habilis is the first of the Homo genus to come forth at around 2.8 million years ago. They used tools, which have been documented archaeologically. Most were tools made of stone. Encephalization began to evolve after that so that Homo erectus developed and emigrated from Africa about 1.9 million years ago. Later came Homo ergaster, who lived mainly in Africa. Homo erectus and Homo ergaster first used fire and had more complex tools to work with. There are other species that have been found as later ancestors. These include Homo rhodesiensis, Homo antecessor, Homo heidelbergensis, and Homo neanderthalensis. The earliest Homo genus that had modern features entirely came out of the Middle Paleolithic period in Ethiopia. The Neanderthals and the Denisovans probably evolved from a type of Homo erectus that had already left Africa. Hybridization or interbreeding is a part of human prehistory. There was Neanderthal-human interbreeding in the Middle Paleolithic and Upper Paleolithic eras. It probably also happened with the Denisovans. All of this points to a network of inheritance rather than a linear ascension from archaic man to modern man.

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EVOLUTION BEFORE THE HOMO GENUS It is sometimes helpful to understand how evolution proceeded prior to the arrival of the Homo genus. Primates on earth have existed for 65 million years. There are several animal species that have been termed the first primates”. These were likely the Plesiadapis from North America and the Archicebus from China, although there were others in Eurasia. They evolved into several life forms, some of which became modern great apes. The catarrhines or the genus Catarrhini were early ancestors to monkeys that liked in Kenya, arriving at about 24 million years ago. The archaic species had tails and were not bipedal. About 22 million years ago, in the early Miocene period, there were many different catarrhines that lived in trees in East Africa. There were many descendants of these species. The earliest Old-World Monkeys were found to date back 20 million years ago, leading to the ape lineage, which began about 13 million years ago. Most lived in tropical and sub-tropical environments in places as far north as Spain and Austria. Gibbons have no fossil record for their origins but these were the first divergence of the great apes. The Orangutans followed these. There were those in the Nakalipithecus genus in Kenya found to be the last common ancestor for gorillas, chimpanzees, and Homo sapiens. The first gorillas split off about 4 to 8 million years ago and the chimpanzees followed. There is little fossil record for these early chimpanzees and gorillas, partly because the climate tends to dissolve bone. There is little fossil record also for the divergence of hominins from the gorilla and chimpanzee lineages, with the early human lineage being the Sahelanthropus and Orrorin. These were followed by the Ardipithecus genus. It is argued that these primates engaged in selfdomestication because of behavioral adaptations occurring in evolution at the time. Australopithecus existed in East Africa around 4 million years ago but became extinct about 2 million years ago. There were several species that have been discovered, as well as some subspecies. At least one species, referred to as Little Foot, had an opposable big toe, indicating that the species was probably a good climber. Because of predation, it is thought the nested in trees.

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EVOLUTION OF THE HOMO GENUS As mentioned, the earliest human and the first to have used tools was Homo habilis, who was the prototypical caveman”, using stone tools. The Homo habilis brain wasn t very big but it was believed to have been wired more efficiently. Encephalization occurred soon after this, which resulted in Homo erectus and Homo ergaster. In fact, the cranial capacity doubled in size at the time of their arrival. These early humans were likely the first to make use of fire and more complex tools. These were the first also to leave Africa to all parts in the Northern Hemisphere in Eurasia. Modern humans probably evolved from Homo rhodesiensis, Homo heidelbergensis, or Homo antecessor, migrating out of Africa the last time about 55,000 years ago, although some believe it could have been as early as 100,000 years ago. These replaced the local populations in Eurasia of the Denisovans, Neanderthals, Homo floresiensis, and Homo luzonensis. Archaic Homo sapiens were the original prototype of modern man. At some point, there was the evolution to more modern cultures, language, and complex stone tools, which may have occurred about 50,000 years ago, although there is disagreement as to whether this happened all at once or gradually over time. Eventually, all of the Homo genuses died out and became extinct except for Homo sapiens. We cannot underestimate the impact of the environment on human evolution. There was, for example, the super-eruption of Lake Toba in Indonesia about 70,000 years ago that had global implications on evolution. It is believed that most humans were killed and the population dwindled before taking off again over time. This phenomenon is referred to as a population bottleneck. Homo habilis directly diverged from Australopithecus in South and East Africa about 2.5 million years ago. Stone and animal bones were used as tools by this primitive form of man. There are some who believe this species should be moved back to the Australopithecus genus because they were adapted to living in trees and did not move easily as bipedal primates. Homo erectus was first identified in Indonesia. It was originally called a form of Anthropopithecus rather than one of the Homo genera. The skeleton, called Java man, was compared to Peking man at a later date and it was determined that both were the same and they were renamed to become Homo erectus. They were likely wiped out by the Toba catastrophe because of their proximity to Indonesia during the super-eruption. Homo ergaster is either a separate species or a subspecies of Homo erectus.

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With the increase in brain size in Homo erectus, there was also a decrease in intestinal capacity and a lesser efficiency of the brain in terms of nutrient use. This is what may have led to cooking food so it could be more nutritious for the body and brain. Peking Man in Asia is an example of Homo erectus. Intermediate species include Homo cepranensis, found in Italy, Homo antecessor, found in Spain and England, and Homo heidelbergensis or Heidelberg Man. Homo rhodesiensis or Rhodesian man is believed to be related to or the same as Homo heidelbergensis. We know more about Neanderthals and Denisovan man, who were more recent. Neanderthals lived in Europe and Asia around 28,000 to 400,000 years ago. The Neanderthals were particularly adapted to cold environments; they are believed to be similar to what s seen in the Inuit population and they had larger brains. Researchers believe that Neanderthals lost less body heat and could see better than modern humans. They needed a larger brain to control their larger bodies and may have been physically better than humans. They had fewer social skills and lesser use of tools compared to anatomically modern humans. There were more humans in terms of numbers so the Neanderthals were replaced. Modern man coexisted with Neanderthals for 10,000 years in Europe. The Denisovans were first found in Siberia. DNA was able to be sequenced and carbon dating showed they lived around 40,000 years ago. They come from the same lineage as the Neanderthals and may also have coexisted with anatomically modern humans. As mentioned, there is evidence of interbreeding with humans in Southeast Asia. Denisovans and Neanderthals are more closely related to one another than they are to humans. Homo floresiensis is an interesting species that existed about 190,000 to 50,000 years ago. These are sometimes called hobbits because of their small size. They carry a common ancestor to modern humans but followed their own evolutionary pathway. They were about one meter in height and had small brain capacities. Some believe that what was found to support this as a separate species was not enough to call them a separate species but instead represented a human with pathological dwarfism. The remains were found on the Flores Island in Indonesia, where pygmies can be found. The skeleton was found with human tools. Because others were found to look the same, there is also support for the separate species” idea. The term, Homo sapiens, means wise one” or intelligent one”. Most believe the species was derived from Homo heidelbergensis although interbreeding of more than one species could also have happened. The Toba Catastrophe led to a population bottleneck and likely played a role in the genetics of modern man since that time.

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TOOL USAGE Using tools is believed to be a sign of human intelligence. Increased use of tools led to the ability to use meat products that were rich in protein as well as the cultivation of plant products. The most primitive tools were sharp-edged stones or broken bones. While many species use tools, it is believed that humans are most notable for using complex tools. Stone tools have been found in Kenya and Ethiopia. This coincided with the finding that there have been structural changes in the hands and wrist that made tool use easier. Stone tools date from 3.3 million years ago. There were basic tools like choppers used in the Paleolithic or Old Stone Age. The Paleolithic Age stopped about 10,000 years ago at the end of the last Ice Age. There are three subdivisions to the Paleolithic period, which extended from 350,000 years ago to 10,000 years ago. The Acheulean period was when Homo ergaster made stone hand axes. Things like scrapers, needles, and slicers were made. Flint tools were made by Neanderthals and Cro-Magnon man. Bone tools were also made.

BEHAVIORAL CHANGES After each stage from one species to another made their transition, things changed rapidly and advanced; however, after a change, things developed more slowly. There is debate as to whether early Homo sapiens had similar language skills, complex symbolic thought processes, and creativity that currently exists today. Most believe they were well adapted to hunting and foraging. At around 50,000 years ago, there was what is called the great leap forward” in Eurasia and there was big game hunting along with more modern behavior. Others believe the process was not a great leap but was more gradual. Humans buried their dead, made clothing, and trapped animals. The first evidence of cave painting dates from that time. Simple artifacts, like buttons, bone needles, and fish hooks have been found from this time period. Other examples of modern behavior from that time period were things like jewelry, specialized tool-making, living space organization, death rituals, art and paintings in caves, and barter trading patterns. Again, it is debated as to whether this was a sudden occurrence in mankind or a gradual series of events.

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MODERN HUMAN EVOLUTION The concept of modern human evolution refers to the genetic drift patterns and adaptation that have occurred within the anatomically modern humans, who first appeared in the Middle Paleolithic period. Some modern man was isolated for many thousands of years, which has led to genetic variation of the species. There have been selection pressures on modern man that mainly affected those in Eurasia and in sedentary farmers, partly because of the rise and fall of glaciers. There are some humans who adapted to specific climates, such as those who can tolerate high altitudes. Some of this was acquired by interbreeding with archaic humans. Some studies have shown that mixtures with Neanderthals led to changes in hair color, risk for depression, smoking addiction, sleeping patterns, skin tone, and height differences in humans. The last glacial maximum led to selection pressures in the Eurasian human. Phenotypes linked to Caucasian skin coloring dates back to 19,000 years ago during the last glacial maximum. Blue eyes date back to 14,000 years ago in Italy and in the Caucasus. The adaptation leading to the cold climate adaptation seen in Inuit populations also dates back to the last glacial maximum period about 20,000 years ago. The largest brain volumes is seen in people who come from the Arctic and Siberia. The Holocene period involved large evolutionary adaptations in humans. This period of time was when there were more farmers in Eurasia, changes in diets, and the domestication of animals. East Asians developed the ability to digest lactose and learned rice domestication. Certain individuals who practiced extended free diving in the ocean had an enlarged spleen so they could hold more oxygen-rich blood cells. Menopause has been occurring later, especially since industrializations. Some populations have had selective pressures that lead to lower blood pressure, lower cholesterol, and lower blood sugar levels. The human reproductive period has lengthened.

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KEY TAKEAWAYS •

The common ancestors of mankind also gave rise to gibbons, orangutans, gorillas, bonobos, and chimpanzees.

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Chimpanzees and bonobos come from the same genus and are our closest extant relatives.

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The first of the Homo genus was Homo habilis, who first used primitive stone tools.

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Homo sapiens probably evolved from Homo heidelbergensis or Heidelberg man.

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There is evidence of early human inbreeding with Denisovans and Neanderthals.

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The migration out of Africa probably happened more than once to give rise to dead-end species, such as the Neanderthals and Denisovans.

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The last human migration out of Africa happened about 55,000 years ago to give rise to all non-Africans in the world.

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The Toba Catastrophe killed much of the human population and redirected our gene pool.

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QUIZ 1. What is not a characteristic that defines a difference between archaic man and modern man? a. Archaic man had a prominent brow ridge. b. Archaic man did not walk erect. c. Archaic man did not have prominent chin. d. Archaic man had a thicker skull. Answer: b. Each of these is true of archaic man versus modern man, except that archaic man also walked erect as does modern man. 2. When did modern man first appear on earth, according to archaeological digs? a. 450,000 years ago b. 310,000 years ago c. 160,000 years ago d. 30,000 years ago Answer: c. According to archaeological digs, modern man can first be identified as arriving on earth about 160,000 years ago. 3. Which of these species is our most distant common relative in terms of evolution? a. Gorillas b. Bonobos c. Gibbons d. Orangutans Answer: c. Gibbons were the first of these to diverge from the human lineage so they represent our most distant primate relative.

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4. Which genus of ancient man was the first to be fully bipedal? a. Ardipithecus b. Australopithecus c. Orrorin d. Sahelanthropus Answer: a. About 5.6 million years ago, the genus Ardipithecus was the first to be fully bipedal among our human ancestors. 5. What provides the best evidence for determining when the different Hominid species diverged in evolutionary time? a. Skeletal remains found in archaeological digs b. DNA sequencing c. Physical measurements of modern species d. Immunological cross-reactivity with modern species Answer: b. DNA sequencing of homologous proteins provides a sort of molecular clock that is probably the most accurate in determining when species diverged among Hominids over evolutionary time. 6. When did modern humans leave Africa the most recent time? a. 2.6 million years ago b. 800,000 years ago c. 55,000 years ago d. 9000 years ago Answer: c. Modern humans exited Africa about 55,000 years ago, although there is evidence that earlier humans left Africa as much as 2.6 million years ago.

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7. Which species of the Homo genus did not likely leave Africa at all? a. Homo neanderthalensis b. Homo floresiensis c. Denisovan man d. Homo habilis Answer: d. According to modern theories of migration, Homo habilis did not likely migrate out of Africa, although each of the rest of these did leave a fossil record outside of Africa. 8. What was the major implication of the Toba Catastrophe or the supereruption of Lake Toba in Indonesia 70,000 years ago? a. Other species were wiped out so man could ascend. b. Many if not most forms of humans across the globe were killed. c. There was an increasing dependence on marine life for food. d. Mankind came to be more social and survived in social groups. Answer: b. There was a great reduction in mankind s numbers across the globe, with many early Homo species getting wiped out altogether. 9. What were the most likely earliest tools used by early man? a. Flint tools b. Axes c. Bows and arrows d. Chipped stone Answer: d. The chipped stone tools may have been natural or made by early man, who also developed the dexterity and hand strength to use them.

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10. What modern human adaptation happened near the last glacial maximum rather than later in the Holocene period? a. Ability to domesticate animals b. Caucasian genetics c. Lactase persistence d. Farming communities Answer: b. Caucasian genetics, blue eyes, and cold adaptation happened during the last glacial maximum, while the Holocene period is associated with farming, domestication, and lactase persistence.

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CHAPTER NINE: EXTINCTION The topic of this chapter is extinction, which is the final termination of a specific organism type or species. This has occurred to 99 percent of all species that have ever lived on earth. We talk about background extinction, which happens over a period of time for a variety of reasons, as well as extinction events that have occurred in the earth s history, leading to the mass extinction of many of the species on earth at roughly the same time.

EXTINCTION BASICS Extinction involves the termination of a group of organisms, usually referring to an organism s species. Almost always, this is preceded by the loss of ability of the organism to breed to a degree that keeps up with the death rate. It is not something that can easily be determined prior to the actual fact of the extinction but is discovered after it has happened. There are certainly those that are called Lazarus taxa”, which is the reappearance of a species after it has been considered extinct. In actuality, the species was not actually extinct but was able to revive its numbers. The time period between the presumed extinction and revival can be as much as millions of years. It is something often thought of as applying to fossils only but there are examples of recently extinct species of insects, plants, mammals, fish, and other organisms that have left no fossil records but were later found after their presumed extinction. More than 99 percent of all species—more than five billion of them—have arisen but became extinct during some point in the earth s existence. There are 10 to 14 million species on earth with only 1.2 million documented to date. Other researchers believe there are more than 1 trillion species on earth, meaning that an extremely small percentage has been described. As you have learned, species tend to find an ecological niche in order to survive, even with competition. If the ecological niche disappears or competition is fierce, the species can die out. The average lifespan of a species on earth is 10 million years before it becomes extinct, although there are species called living fossils that are long-lasting and have not changed for many millions of years. Later on in this chapter, we will talk about mass extinctions and extinction events, which are uncommon and result in the loss of many species relatively suddenly in evolutionary time. We

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will also talk about the problem of extinction in present time. There are many species that have been lost and will continue to be lost because of human presence on earth. Extinction becomes inevitable when there aren t the physical numbers of organisms of a species that can reproduce to have offspring. The phenomenon of functional extinction happens if there are living specimens that are too sparsely distributed to find mating partners, when the organisms are in poor health, or because there are not enough organisms that can reproduce with one another. When studied in ecology, the term extinction” actually refers to local extinction, where the species disappears from its typical area of study but it still exists somewhere. A better term for this is extirpation. Most of the time, extirpation is followed by replacement with another species or with reintroduction of the species. An extant species is one that is not extinct. Threatened or endangered species are extant but are at risk of extinction. Humans are currently attempting to preserve species that have become endangered. The International Union for the Conservation of Nature or IUCN has different categories for the status of the species. For example, there is the distinction of being extinct in the wild” when there are no known specimens that have survived in the wild and there is no ability to repopulate them in the wild. These are mostly species that are housed in zoos. There is also the phenomenon called chains of extinction”. This happens when the extinction of one species leads to the extinction of others. Keystone species are those that affect the biodiversity and survival of a great many other species. The wolf is an example of a keystone species. An organism can undergo pseudoextinction. This is when a parent species becomes extinct but a subspecies or daughter species remains extant. This causes the old taxon to disappear, the splitting of a species into more than one taxon, called cladogenesis, or the transformation of a species, referred to as anagenesis. Pseudoextinction cannot easily be proven unless there is good genetic or fossil evidence that the parent species is truly extinct. There are several causes of a species extinction. It can come on quickly when a habitat is destroyed by pollution or natural disaster. It can take a long time if the problem is due to superior competition by others. The phenomenon of extinction debt occurs when extinction is delayed but becomes inevitable. Some extinctions can be due to technological disasters or climate change.

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There are conservation groups that are attempting to reduce the impact of human activities on the phenomenon of extinction. Humans cause extinction in many ways. These include pollution, destruction of the habitats, overharvesting, overhunting, and introduction of invasive species. Most human-caused extinction comes from human overpopulation. About 800 extinctions have been documented since 1500 CE, when the term modern extinction” is arbitrarily said to have started. If there has been a buildup of deleterious mutations or if deaths exceed the species adaptation to the habitat, the species will become extinct. Small populations are at the greatest risk of extinction because there will be fewer advantageous mutations. The buildup of deleterious mutations that contributes to the decreased fitness of a smaller population is called a mutational meltdown. Another thing that contributes to what s called background extinction is having a limited geographic range. This is less of an issue in mass extinction. Those populations with a deep gene pool are more robust and will survive better in poor conditions. A loss of genetic diversity increases the chance of extinction. Population bottlenecks are when a population stalls out and there is a limit to the number of reproducing individuals. Population bottlenecks will increase the chance of inbreeding. A species can be threatened to extinction because of genetic pollution. This is when there is uncontrolled hybridization that favors the competitive status of the hybrid or introduced species. Selective breeding can drive out the original population. The same can happen when two separate populations of organisms are brought together. Rare species are especially at risk. An example of this is the introduction of the domesticated water buffalo, which has driven out and endangered the wild buffalo. A species gene pool involves the variety of genetic information of its members. Large gene pools have a high degree of genetic diversity and robust populations that survive selection pressures. Inbreeding and population bottlenecks will decrease the genetic diversity of a species, which will increase the chances of extinction. We talked about the Toba catastrophe that was probably why many non-Homo sapiens died off, leaving humans as the surviving species. The largest contributing factor by humans to extinction is habitat destruction. Agriculture, logging, urban sprawl, fishing practices, and mining can all play a role; however, agriculture is the main factor involved in this process. Toxicity of the environment can kill a species quickly by rendering them unable to reproduce effectively or directly killing the species.

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A lot as been said about the destruction of the tropical rainforests. This is an extreme but real problem involving habitat degradation. The rainforest is largely replaced with pastures, which do not support the species that need the rainforest to survive. A lesser example is bottom trawling by fishermen, which destroys marine habitats. Global warming leads to diminished resources and can introduce new competitors to existing species that cannot keep up with the competition. The new species can be a predator to the existing species, leading to species extinction. A necessary prey, host, or pollinator becoming extinct can lead to co-extinction of another species. The presence of evolving diseases can lead to extinction of a species. The transportation of animals or plants from one area to another by humans has destroyed many species. This has happened for a long time in situations where livestock or even rats have been released to a new ecological area. Humans themselves can be an invasive species that will destroy the flora or fauna of a new area. Coextinction can happen anytime one species extinction leads to the extinction of another species. This happens because much of life on earth is interconnected. As mentioned, the loss of a keystone species can lead to many other species becoming extinct. Parasites and organisms that are mutualistic can affect other species. If a predator s prey becomes extinct, so does the predator. Climate change is not a new event but the human contribution to climate change is a new event. Fossil records have shown that any time there is climate change, there is the extinction of a species. Amphibians became largely extinct more than 300 years ago when the rainforests collapsed. Climate can destroy a habitat or introduce competitive species. We will talk more about mass extinction next but we should also talk about what s been called the Holocene extinction. This is specifically related to the extinction of many species on earth because of human intervention. Some believe it is currently a very rapid phenomenon that qualifies as a mass extinction event. The current rate of extinction is between 100 and 1000 times that of background extinction. Overconsumption of resources and population growth are the main causes of this crisis. In past human history, extinction was denied as a possibility because people believed in the great chain of life” theory that God created a perfect world where everything had its niche. Nowadays, extinction is a hot topic in the studies of botany, zoology, and other fields of biology. There are a number of governments that have enacted protection laws for endangered species as

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well as a number of organizations that have species preservation as their main goal. There are some species that have been driven to extinction or near-extinction by poaching or overhunting of a species. There are ethical reasons why people oppose extinction. There is also an advantage to the world to have a greater degree of biodiversity. Ecotourism suffers if species become extinct, which is why nature preserves have become important. One of the big problems with human-related extinction is that humans often favor day to day issues over species conservation. Agricultural needs have led to slash and burn agricultural practices. There are rare events when man successfully plans the extinction of a species. The main purpose of this is to eradicate infectious diseases. Smallpox has been driven to extinction. The rinderpest virus, which affects cattle, has been rendered extinct. The organism that causes yaws and the organism that causes polio are currently being eradicated. Some have advocated for the extinction of certain mosquito species that carry many diseases. The phenomenon of de-extinction involves using genetics and technology to revive an extinct species through cloning. This has been proposed for mammoths and for the Pyrenean ibex. This has already been tested for the Pyrenean ibex, which was cloned so that embryos could be transferred into female mountain goats. While some aspects of the process have been successful, no clone to date has survived past a few minutes of life due to birth defects.

BACKGROUND EXTINCTION Background extinction is referred to as normal extinction. This is measured as the background extinction rate throughout history prior to the contributions of humans and in between major extinction events. Extinctions are a normal part of evolution and occur at differing rates throughout geologic time. Background extinction rates can be evaluated by determining the number of species that become extinct over time. It can also be measured in million species years. If one species goes extinct every year out of a million species, this is what is referred to as million species years or MSY. Finally, the background rate can be measured as the species survival rates over time. This lists the number of years it takes for a species to go extinct. There are estimates given for the average lifespan of a species in millions of years. Mammals tend to have the shortest species lifetime, while invertebrates can live the longest, with species living around 10 million years before dying out. It is difficult to make these types of estimates

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because no one knows exactly what defines a species. Species extinction rates, even of background extinction, is not stable over time.

MASS EXTINCTION Mass extinctions are also referred to as extinction events or biotic crises. It results in a major loss of biodiversity on earth over a short period of time. No one knows the exact number of extinction events there have been, mostly because it is hard to define what is major and what is meant by a rapid change in biodiversity. Extinction events are usually defined based on their effect on multicellular organisms because it isn t known what the effect has been on microbes of the earth. Marine animals are most used to assess these events because their fossil records are the most accurate and stratification is easier to determine in water-based environments. There have been five major mass extinction events and many more minor events throughout geologic history. We will talk about these events and their possible causes. The first extinction event occurred at the transition between the Ordovician and Silurian eras about 450 million years ago. There were two events that killed off about 60 to 70 percent of all the earth s species. The earth was warm prior to the events, which were a major fall in sea levels affecting coastal areas and glaciation, which cooled the earth, killing off many marine organisms. The Late Devonian extinction happened at the transition between the Devonian and Carboniferous eras. There were multiple events that killed off 70 percent of species and that lasted 20 million years. No one knows how many events contributed to this but it primarily affected marine animals. No one knows what events likely caused this extinction. The largest extinction on earth killed off up to 96 percent of all species. It was called the Permian-Triassic extinction event, killing off insects, trilobites, and many plant species. Mammal-like reptiles died off and it took 30 million years for vertebrates to recover from this great dying event. No one knows if it was due to one or several events but it may have been caused by volcanic eruptions, meteor impact, or climate change causing the release of methane from the oceans. The Triassic-Jurassic extinction event occurred 200 million years ago, killing off about 75 percent of all species. Archosaurs, large amphibians, and therapsids were largely made extinct. It allowed the dinosaurs to ascend without competition. No one knows what caused it but it caused much of the earth to become much drier.

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The Cretaceous-Paleogene extinction event, formerly called the KT extinction. This happened 66 million years ago, resulting in the descent and extinction of the dinosaurs, with the rise of birds and mammals. Seventy-five percent of all species became extinct. It is believed to have been caused by a massive meteor strike near the Yucatan Peninsula. It is harder to identify the presence and timing of early or older extinction events for several reasons. Older fossils are buried too deeply to evaluate in many cases. Dating older fossils is harder to do. Prehistoric environmental events can damage deposition of deposits. Non-marine fossils are also very hard to evaluate if they are older. Many also conclude that we are living in what s called the Holocene extinction, which is caused by the industrialization of the earth by humans. Mass extinction has already occurred and oneeighth of all plant and animal species are threatened with extinction. What hasn t been talked about so far is the Great Oxygenation Event in the Precambrian period. This happened 2.4 billion years ago and was caused by the development of photosynthesis and from the subsequent rise in oxygen levels on earth, which likely disrupted the life cycles of many microbes. While we think of extinction events as destroying life on earth, it sometimes accelerates the evolutionary process. The new species that emerges isn t necessarily superior to the extinct species but it simply becomes dominant over other species. Mammal-like and mammals existed from the time of the dinosaurs but they could not ascend because of the niches dominated by the larger vertebrates. The end-Cretaceous mass extinction created vacancies in multiple niches in order to allow the ascendency of mammals. Groups that do survive extinctions don t always ascend but can have a decrease in their overall numbers, going into a gradual and long-term decline themselves. Extinction events are not generally predictable but there is some periodicity to them, occurring every 26 to 30 million years on average. It is not true that species numbers build up to such a degree that a mass extinction becomes an inevitable thing. As we have been discussing, the exact cause of mass extinctions is largely unknown or at least may be multifactorial. There is usually some type of shock to the environment that is compounded by a long-term stress in the environment. Either one of these things alone is not usually enough to cause a mass extinction. Finding the exact cause of a mass extinction, however, can be very difficult.

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There are three main categories of mass extinction events. Remember that any given extinction can have more than one cause. One of these is called flood basalt events, which usually involve eruptions. The second is reductions in sea level. A third is an asteroid impact, which has only been positively associated with one major extinction event. Volcanic events inhibit photosynthesis, which can damage the food chain, be emitting dust particles. Sulfur oxides can be emitted, which causes acid rain and the poisoning of organisms. Carbon dioxide emissions can also lead to global warming after the dust dissipates. Reduction in sea levels can contribute to mass extinctions because they disrupt the continental shelf area life, which is the most productive area in the ocean. This can cause mainly marine extinction but could also trigger changes in the weather pattern. Global cooling itself can cause a reduction in the sea level. This phenomenon has been impactful in all of the major extinction events. Asteroid impacts of sufficient size can raise dust particles that block photosynthesis, cause large tsunamis, trigger forest fires, and cause acid rain to fall. Outside of the Cretaceous-Paleogene extinction event, the impact of these phenomena is not known in earlier extinction events. Sustained global cooling can force species toward the equator and will lock up water on earth into glaciers. This is cyclical in nature and isn t believed to have had a major impact on mass extinction events, although they can contribute to the stress in the environment. Global warming kills temperate species or forces them to the poles. It has the greatest effect on polar species themselves, melting the ice caps and possibly triggering anoxia or lack of oxygen in the ocean. This is believed to have contributed to several minor and a few major mass extinction events. Releases of methane gases in the marine environments worsen the problem because methane is a strong greenhouse gas. Methane can be released from the marine areas by sudden global warming. Anoxic events happen when layers of the ocean become extremely low in oxygen. Most of these events are due to sudden global warming from sustained and massive volcanic eruptions. This is likely a contributing factor for many of the major and minor extinction events. Another possible contributor to extinction is an overturning of the saline environments of the ocean. Surface water is more concentrated and sinks to the bottom of the ocean, causing the deeper waters that lack in oxygen to rise to the surface, killing the upper marine life. This is a form of an anoxic event and occurs at the beginning and end of glaciation, during global warming or global cooling.

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Plate tectonics and continental drift may somewhat contribute to mass extinctions by changing weather patterns and things like wind and ocean currents. It is not likely, however, that disease infestation could have ever been the cause of mass extinctions because it would have to have affected the majority of the species on earth.

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KEY TAKEAWAYS •

Extinction is a natural part of the evolutionary process.

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Often extinctions don’t happen in isolation but involve disruptions in the food chain and competition changes in the environment that result in other extinctions.

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It is sometimes difficult to gauge extinction because it involves identifying species, which is also difficult to do.

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Background extinction rates vary throughout geological time but happen in the absence of a mass extinction event.

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There are multiple factors that contribute to mass extinction, which usually involves long-term pressures on the ecosystem and a short-term shock to the environment.

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There have been five major extinction events and numerous minor extinction events in geologic time.

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QUIZ 1. What is true of a Lazarus taxon? a. It mainly applies to those organisms that have shown up in the fossil record. b. It does not exist today because researchers keep closer track of extinct species. c. It involves all living and previously living forms of life, even if their presumed extinction was recent. d. It mainly involves species with long lifespans that reproduce under circumstances where the taxon’s numbers are rare. Answer: c. The phenomenon of the Lazarus taxon applies to past or presently living organisms that were once considered extinct but have been later rediscovered. All types of organisms can have Lazarus taxa. 2. A species that has survived unchanged for many millions of years on earth is called what? a. Extant species b. Lazarus species c. Elvis species d. Living fossil Answer: d. A living fossil is a type of species that has survived relatively unchanged in nature for hundreds of millions of years for whatever reason. 3. What is a species called that affects the populations of many other species called? a. Umbrella species b. Keystone species c. Apex predator d. Flagship species

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Answer: b. A keystone species is one that affects the population of a number of other species. Some can be apex predators but they do not have to be to be called a keystone species. 4. What least likely happens in a pseudoextinction? a. The species is transformed somehow b. The species undergoes cladogenesis c. A subspecies takes over for a parent species d. The species becomes extant again Answer: d. In most cases, in a pseudoextinction, the species is transformed, a subspecies or daughter species becomes prominent, or the species breaks into at least two other species. It would be rare for the species to become extant again because that isn t what defines a pseudoextinction. 5. What is the number one cause of human habitat degradation? a. Mining b. Urban sprawl c. Fishing practices d. Agriculture Answer: d. Each of these can cause degradation of the habitat but agriculture plays the largest role in this problem. 6. What is not true of climate change and extinction? a. Climate change can destroy habitats b. Climate change is a manmade phenomenon c. Climate change can introduce competition of a species d. Climate change will lead to extinction of species Answer: b. Climate change does lead to extinction for many reasons but it is not just a manmade phenomenon. It has occurred since the dawn of the earth for reasons other than human interference.

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7. What is not true of mass extinction events? a. They mainly apply to multicellular organisms b. They are usually measured using marine fossils c. They occur at predictable times d. They are sometimes difficult to define Answer: c. Each of these is true of mass extinction events except that they aren t predictable in their timing. 8. What species did not die off as part of the largest extinction event so far, called the Permian-Triassic extinction event? a. Trilobites b. Mammal-like rats c. Insects d. Dinosaurs Answer: d. Each of these died off in this extinction event except for the dinosaurs, which hadn t ascended yet at this time. 9. What is the least likely contributor to short-term shocks that have resulted in extinction events? a. Asteroid impacts b. Volcanic eruptions c. Sun spots d. Reductions in sea level Answer: c. Each of these can cause a shock to the environment except for solar phenomena, such as sun spots.

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10. What is not a way that volcanic eruptions can cause mass extinctions? a. They can trigger an ice age b. They can cause acid rain c. They can emit carbon dioxide, which causes global warming d. They can emit dusts that inhibit photosynthesis Answer: a. Volcanic eruptions can do all of these things but, other than causing short-term temperature reductions, they trigger global warming rather than ice ages.

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CHAPTER TEN: EVOLUTION OF REPRODUCTION This chapter discusses issues related to the evolution of reproduction. There are basically two broad categories of reproduction, which are asexual reproduction and sexual reproduction. There are evolutionary advantages and disadvantages of both that will be compared in this chapter. With sexual reproduction, in particular, there are complex variables involved in mate selection, which will also be covered along with the evolutionary issues related to human sexuality and human sexual reproduction.

ASEXUAL REPRODUCTION Asexual reproduction is an early form of reproduction from an evolutionary perspective. In this type of reproduction, offspring inherit the genes of the parent organism only. There are no gametes and the number of genes and chromosomes does not change. This is the main type of reproduction for archaea and bacteria, which are exclusively single-celled organisms. Fungi and plants also have the capacity for asexual reproduction, although it might not be their only mode of reproduction. In the chapter on genetics, we talked about some quasi-sexual reproduction in prokaryotes, which include conjugation, transduction, and transformation. Multi-celled organisms rarely have strict types of asexual reproduction but are mostly sexual. This is especially true of animals that are multi-cellular. There are advantages and disadvantages to each form of reproduction. Asexual reproduction mainly involves binary fission. In this activity, the parent organism divides with two daughter organisms taking its place. It only happens in archaea and bacteria. While a similar process takes place with regard to eukaryotic mitosis, in which a cell also divides to make daughter cells but this does not truly represent the same thing as binary fission. It is possible for a cell to participate in multiple fission, which is called schizogony. This usually happens in some types of parasitic protists. Multiple nuclei are made in a single parent cell that later divides into several daughter cells. There are three possible things that can happen with schizogony. In merogony, there are multiple daughter cells originating within the same cell membrane; each daughter cell is a merozoite. The phenomenon of sporogony is similar but results in sporozoite formation. The process of gametogony yields multiple microgametes.

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Budding is another type of asexual reproduction, often done by yeast organisms. There is a mother cell and a daughter cell created, in which the daughter cell is smaller. It happens in multi-cellular organisms, such as the hydra animal, which reproduces this way. Eventually the buds grow and mature, becoming parent cells themselves. Some parasites, such as Toxoplasma species, use internal budding, which is also asexual. Two or more daughter cells are made inside the mother cell. Then the daughter cells consume the mother cell before there is separation of the daughter cells. Some worms also participate in this type of budding, although they also do external budding. They also make cysts. Vegetative propagation is also an asexual process. There are new plants produced from the parent organism without syngamy or meiosis. This is seen in plants that create miniature versions of themselves. There are plants that make stolon, like strawberry plants, plants that make rhizomes, and plants that make tubers or bulbs, such as tulips. Others can shoot off to make clonal colonies, which involves clones of the parent plant that cover a relatively large area. Sporogenesis or spore formation happens in some multi-cellular organisms. It is not considered asexual if meiosis occurs and if fertilization is part of the spore formation. Some algae and post plants produce spores that are haploid and similar to gametes. The spores develop into gametophytes that are multi-cellular and that make gametes using the mitotic process. These processes result in an alteration of asexual and sexual reproduction. Spore formation that involves both meiosis and fertilization is not asexual. True spore formation that can be considered asexual must involve mitosis, which gives rise to mitospores that can create a new organism after they have dispersed. This happens in some algae and in fungal organisms. This is actually a rare phenomenon in these organisms. Fragmentation is a type of asexual reproduction in which just a fragment of the parent organism makes an entirely new organism that is complete. Planarians and other types of worms can do this as can sea stars and other marine animals. Lichens and liverworts are plants that do this. This is an asexual process. When echinoderms do this, it is called fissiparity. There are two reproductive processes that do not involve a male gamete. These are parthenogenesis and apomixis. With parthenogenesis, and unfertilized egg can create a new organism. Plants, some insects, some reptiles, and some bird or shark species can do this. Apomixis involves plants that can make sporophytes that are not fertilized. Ferns, flowering plants, and rarely other seed plants will do this and will make seeds without the fertilization

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process. Male apomixis is rare but possible, in which the pollen or male gamete makes the genetic material of the entire embryo. As mentioned, some species have the ability to alternate between asexual and sexual reproduction. This is called heterogamy. Aphids will do this, depending on the environmental conditions. So can some bee species, reptiles, birds, and some amphibians. Daphnia is a freshwater crustacean that will undergo parthenogenesis under conditions of a sparse population but will move on to sexual reproduction when competition is great enough. Some animals engage in polyembryony. This is when the egg is fertilized but the early embryo breaks up into multiple identical clones. This is obligatory in some animals but a sporadic thing in other animals, such as mammals, including humans. Throughout evolution, there are some that have been successful in reproducing asexually throughout the course of evolutionary time. Bdelloid rotifers create only females and do so asexually. They have done this for millions of years. Stick insects engage in parthenogenesis only—also for the past many millions of years.

EVOLUTION OF SEXUAL REPRODUCTION When it comes to evolution, sexual reproduction came along after asexual reproduction. Many types of organisms participate in this process. A few organisms already mentioned have lost the ability to reproduce sexually or have developed things like parthenogenesis and apomixis in order to circumvent dependence on sexual reproduction. Prokaryotes developed sexual reproduction about 2 billion years ago, and eukaryotic organisms developed it as well from a common eukaryotic ancestor. In sexual reproduction, recombination occurs in the making of gametes, and the genotype of the offspring is a mixture of the genotypes of the parents. It does not create identical offspring as the parent, which is what happens in asexual reproduction. As you will see, there are evolutionary advantages to sexual reproduction, which is why it has persisted for so long in the evolutionary process. Even so, there are disadvantages to the process of sexual reproduction. There is a population expansion disadvantage. Because sexual reproduction requires a male and female member, only half of the population can carry the offspring, leading to a decreased number of offspring than can be gotten through asexual reproduction. This is referred to as the two-fold cost of this type of reproduction.

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If there was a species that developed a mutant that could reproduce asexually along with the population that needed to reproduce sexually, the numbers of mutants would double with each generation, outstripping the sexual reproducers. Even if there was no such thing as only females bearing offspring and all organisms could bear young, there would be an energy cost of copulation that involves adequate energy to come together at the right time and in the same space. In addition, a sexually reproducing species passes on just half of its genetic material to the next generation. This is true only of those organisms that make haploid gametes. Other species don t make males and females but make one type of gamete. These organisms pass all of their genes onto their genetic offspring. There are advantages to sexual reproduction that make it preferable to the organism. In general, the two parts to sex are the fusion of genetic material and the differentiation into two different genders. There are organisms that do not do both of these things. If you think about it, sex both increases genetic diversity, while the differentiation part decreases genetic diversity. Hermaphroditism does not decrease genetic material by half because it creates offspring that are of both genders. Sexual reproduction can be advantageous by combining beneficial mutations in the same offspring. It increases the spread of good traits. Sex also brings together bad mutations in the same offspring to create such an unfit organism that the genes are removed from the population. Finally, sexual reproduction can create fitter organisms than the parents. The process of DNA repair during the process of meiosis can decrease the chances of damaged DNA getting into the progeny and increases offspring fitness. Because there are homologous genes from the opposite parents, recessive genes that are deleterious are masked by normal genes that are dominant over the recessive gene. Some theorize that sexual reproduction decreases genetic variation because it can weed out chromosomal rearrangements and other major genetic changes, while allowing minor genetic variations to get through to the offspring. New genotypes can be created better through sex. As mentioned, advantageous genes can be combined from different parent populations to be allowed to spread faster through sexual reproduction. Recombination creates the presence of the two genes together in the same offspring after just a few generations. This just doesn t happen easily in asexual reproduction because the offspring of each organism is identical to each parent.

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In some cases, there are differences in the offspring created sexually compared to those created through asexual reproduction that benefit the heterogamous offspring. These differences are not always explainable but can be seen in organisms that do both sexual and asexual reproduction. Certain water fleas can do either type of reproduction but the heterogamous offspring have better fitness capabilities for reasons unexplained. There is a theory on the persistence of sexual reproduction called the Red Queen Hypothesis. This involves a greater resistance to parasites in organisms that reproduce sexually. In an environmental change, there is the possibility that bad alleles or neutral ones can become more favorable. Offspring might have a genetic makeup that confers resistance to parasitic organisms, leading to better survival of these offspring. There have been studies in support of this hypothesis and that do not support this hypothesis. In sexual reproduction, there can be inbreeding or outbreeding. Inbreeding involves mating with close relatives that allows deleterious recessive genes to be expressed to a greater degree. In outbreeding or outcrossing, mutations are hidden by dominant normal alleles. This is also referred to as hybrid vigor, which is a phenomenon of sexual reproduction. Outbreeding is sometimes abandoned with parthenogenesis taking place if there is too high a cost of sexual reproduction, such as when the population is sparse. How does sexual reproduction help to remove deleterious genes from the gene pool? There are two theories on this. Recombination, for example, only happens in meiosis. In asexual reproduction, it can be difficult to get rid of a bad gene, which can be better removed during the DNA repair that happens in meiosis. With asexual reproduction, you can t usually take back a mutation; you can only add more, which can reduce the species success rate. In addition, sex takes multiple slightly deleterious genes and, through recombination, makes gametes that have fewer mutations than the parent along with those that have more mutations than the parent. Those that are more deleterious are at a much greater disadvantage and get cleared out easily in the natural selection process. The process of sex will compartmentalize bad genes in a few organisms. When and why did sexual reproduction develop? It started about 1.2 billion years ago and probably started with a single eukaryotic ancestor. It probably started with an organism with the ability to repair its DNA, which does not happen in asexually reproducing organisms. The proteins that help meiosis are similar to those that allow for genetic transfer and transformation in archaea and bacteria. Meiosis itself is triggered by adverse circumstances in the environment. It means that, throughout evolution, meiosis could provide a benefit for the organism. Sex may

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also have been triggered by an RNA virus or it may have happened through parasitic DNA fragments entering the cell in ways similar to bacterial conjugation.

ADVANTAGES AND DISADVANTAGES OF ASEXUAL REPRODUCTION It is generally believed that sexual reproduction drives evolution more effectively than asexual reproduction, allowing for increased genetic diversity and the forward progress of evolution. Evolution does happen in asexually reproducing organisms as well. In fact, it happens much more quickly in these organisms. One example of this is the drug resistances seen in bacterial species. Other advantages of asexual reproduction include the following: •

There are minimal energy requirements involved in asexual reproduction.

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Asexual reproduction is highly adaptable to a variety of environments and these organisms are more flexible than sexual reproducers.

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Asexual reproduction does not require a mate.

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Positive genetics can be passed onto subsequent generations.

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There are many forms of asexual reproduction possible.

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Asexual reproduction favors smaller organisms that wouldn’t otherwise survive.

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Plant crops can propagate without seeds or pollinators.

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Crop yields are greater if asexual reproduction is part of the process.

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Maturation of the organisms is fast.

Disadvantages of asexual reproduction include the following: •

Negative mutations are harder to weed out.

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There is limited diversity.

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It is harder to control population numbers.

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There is reduced adaptability to changes in the environment.

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There is a greater risk of overcrowding.

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Change in the environment can wipe out the whole species.

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There is reduced resistance to pests.

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There is a reduced lifespan in these organisms.

MATING SYSTEMS A mating system involves the group structure necessary for sexual behavior. Among animals, mating systems describe how and under what situations the male and female may mate. In plants, the major mating systems are outcrossing, which involves cross-fertilization of organisms, autogamy, which is self-fertilization, and apomixis, which is essentially asexual reproduction. Fertilization can be random or may involve self-fertilization. Animals have their own mating systems. In monogamy, there is one male and one female in an exclusive relationship. There are three types of polygamy in animal systems. In polygyny, which is the most common relationship, one male mates with more than one female but the females are all bound to the same male. In polyandry, one female has more than one male associated with her. This is very rare, except in honeybees. In polygynandry, a few males have sexual relationships with a few females. Another mating system is promiscuity, in which any male and female may mate. This is seen in chimpanzee relationships. The mating relationship does not necessarily get associated with social or parental relationships. Sometimes, the male has no relationship with regard to parenting, while other times, the male is involved to varying degrees. In communal breeding, there is more than one male or female involved in rearing the young. Even in pair bonding and monogamous relationships, there is a fair degree of out-pairings, which can be advantageous to the group by improving fitness or appearance of the young. In promiscuous or polygynous groups, paternal care is rare and some involve no parental care whatsoever. Mating systems can change, depending on the overall circumstances and system mixtures are common. Among humans, the majority of mating systems are polygynous, a few are monogamous, and even fewer are polyandrous. Mating in bacteria involves the actual transfer of DNA from one bacterial cell to another with incorporation of the DNA into the genome. Transformation involves uptake of DNA from the environment. Transduction involves uptake of DNA by an infecting virus. Conjugation involves the transfer of DNA from one cell to another. Archaea can practice a form of mating through forming cellular aggregates. There are bridges that occur between the cells that allow the exchange of DNA. Most protists do not form tissues

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and are unicellular. They were likely the first eukaryotes on earth and they carry the genetic material in some cases to undergo meiosis and sexual reproduction. They can undergo sexual reproduction in stressful environmental conditions. Viruses do not mate in the traditional sense but they do mix their DNA and RNA quite effectively, which is a primitive form of mating.

SEX AND MATE SELECTION Mate selection is one way that evolution can occur in living things. Organisms of many different types will engage in some type of mate evaluation process, which assesses another s fitness and quality. Desirable qualities get passed from one generation to the next through the process of mate selection. In peacocks, for example, there is a certain coloration that increases the likelihood of a female choosing her mate. In many mating systems, there will be one gender that is more selective than the other and the other gender that is more competitive among each other. There are direct benefits and indirect benefits to being choosy about a mate. Direct benefits include increasing the fitness of the choosy sex because of material advantages of having a certain partner. There may be better territory in one mate, increased ability to care for the young, and better protection from the predators. Indirect benefits include getting higher-quality genes from the potential mate. There are several mechanisms by which mate selection is done. There can be direct phenotypic benefits, which involve certain traits that can be inherited from one generation to another. Female cardinals preferentially choose a male mate that has the brightest plumage because it is associated with better parenting skills. It also indirectly benefits the offspring, who get fed better. Sensory bias can also take place. This is seen in certain mating calls in animals and in guppies, who select certain coloration but not for mating purposes. They simply have an affinity for the orange coloration of other guppies. Another mechanism involves the presence of certain desirous traits that become selfreinforcing, even if it increases the animal s risk for predation or causes increased energy expenditure. Peacock feather coloration is related to this. There is no specific genetic benefit except to have more mates. There are certain indicator traits that by themselves mean the mate is of a better quality. In humans, this would be seen as a preference for attractiveness. This could mean that a given trait

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confers some type of protection against disease or that a certain trait indicates a better ability to get necessary nutrients. Another mechanism involves genetic compatibility between two potential mates. In some cases, animals can select their mate based on scent. There have been studies in humans indicating that a woman s scent preference for a male depends on what types of genes the man has in relation to the woman. Dissimilar genes are preferred for disease resistance, according to the theory. In most cases where a preference exists, it is the female that is the choosy sex because she has a greater parental investment compared to the male. This situation can be reversed in some species, especially if there is parental involvement after the birth of the offspring. Species that have this role reversal include seahorses and other fish that involve the female laying eggs into a male brooding pouch. The male raises the young. Male poison-arrow frogs also care for their young and have sex role reversal. Many birds have dual involvement in rearing the young. It has not been documented in mammals. While we think of mate choice in other animal species, it is also an issue in humans. There are short-term and long-term strategies for selecting a mate. Both males and females have mate choice preferences. They are more similar to one another in humans that exists in other species. Women have preferences for tall men who have beards and a lower voice. Women seek out a mate that has better short-term resources, that have the potential for genetic benefits over another mate, or that will facilitate a breakup with her long-term partner. Women tend to prefer long-term benefits to a mate rather than short-term benefits. Males have less of an investment in offspring than females and make many more gametes or sperm cells. Men prefer women who will give them a better sexual experience and who are more attractive. They care less about generosity athleticism, intelligence, and honesty in their female partner. They prefer a sexual partner who is more experienced. They are less likely to look at long-term benefits of a female mate but they do look for facial symmetry, commitment, and femininity, which predicts youthfulness. A low waist-to-hip ratio and larger breasts are also preferred.

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KEY TAKEAWAYS •

Asexual selection likely existed before sexual selection, which occurred in nature first in a eukaryotic ancestor.

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Prokaryotes do engage in primitive mating, which may involve just an exchange of genetic material.

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There are advantages and disadvantages to both types of reproduction when it comes to evolutionary progress.

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There are certain mating systems that are involved in reproductive strategies among the different species.

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Mate selection usually involves one sex that is choosy and one sex that is more competitive.

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Mate selection can be applied to human traits that indicate who a person is more or less likely to have sex with.

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QUIZ 1. What organisms are least likely to engage in asexual reproduction? a. Bacteria b. Archaea c. Fungi d. Animals Answer: d. Animals, particularly multicellular animals, rarely engage in asexual reproduction, while this type of reproduction is much more common in the other organism categories. 2. What phenomenon in bacterial genetics is least likely to be considered “quasisexual” activity? a. Binary fission b. Transduction c. Conjugation d. Transformation Answer: a. Unicellular organisms that engage in these types of behavior are considered quasi-sexual because they involve the uptake of genetic material from outside the parent cell; however, binary fission is a strictly asexual reproductive activity. 3. What type of spore formation is considered truly asexual? a. The creation of diploid spores through mitosis b. The creation of haploid spores c. The creation of spores that are fertilized at later time d. The creation of spores through meiosis Answer: a. Only when the spore formation is made through mitosis and involves diploid spores does it qualify as truly asexual reproductive spore formation.

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4. Which organism does not go through fragmentation, which is the creation of a new and mature organism from a fragment of the parent organism? a. Planarian b. Mushrooms c. Sea stars d. Lichens Answer: b. Fragmentation is an asexual process that involves the ability to create new, mature organisms from a part of the parent. Each of these organism types do this except for mushrooms. 5. What factor most allows two advantageous genes to show up on the same offspring chromosome? a. Recombination b. Sexual selection c. Mate selection d. DNA repair Answer: a. Because there is recombination in meiosis, two separate advantageous genes can show up on the same chromosome after just a few generations. 6. According to the Red Queen Hypothesis, what helps the offspring survive better through sexual reproduction rather than asexual reproduction? a. Increased ability to compete for food sources b. Improved longevity over asexual offspring c. Better resistance to parasites d. Improved hardiness in adverse environmental circumstances Answer: c. According to this hypothesis, offspring made through sexual reproduction have a better resistance to parasites. This has not been proven to be accurate in all practical settings.

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7. What is a disadvantage of asexual reproduction? a. Energy expenditure is too great. b. The organisms are not very flexible. c. It is harder to control population numbers. d. The reproductive process requires pollinators. Answer: c. The fact that population numbers are harder to control and overcrowding can happen is a major disadvantage with asexual reproduction. 8. What type of mating system is involved in honeybee relationships? a. Monogamy b. Polygyny c. Promiscuity d. Polyandry Answer: d. Honeybees engage in polyandry, in which there is one female and multiple potential male mates. 9. What is a more indirect benefit of selecting a good mate for the sex of a species that is choosy about mates? a. Better ability of the mate to fight off predators. b. Better territory of one of the mates. c. Better parenting ability of one mate over another. d. Better genes passed on to the offspring. Answer: d. Each of these is seen as a direct benefit of having a certain mate chosen over another, except for better genes getting passed on, which is considered an indirect benefit of mate selection.

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10. What is not a reason why a choosy gender would select a specific mate? a. The choosy gender prefers similar genetics to her own for the purposes of disease resistance. b. The choosy gender may simply have a preference for certain traits in a mate. c. The choosy gender selects a certain trait because it would indicate better parenting skills. d. The choosy gender may select a trait that confers a genetic advantage to some mates. Answer: a. The choosy gender is more likely to select a dissimilar genetic situation in a mate for better disease resistance.

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CHAPTER ELEVEN: EVOLUTION OF SOCIALITY AND POPULATIONS The focuses of this chapter are evolution within populations and the evolution of social behaviors. Anytime there is a group of individuals in a population, there will be issues of conflict and cooperation, which are discussed in the chapter. Social behaviors are complex but have genetic and evolutionary influences. Topics also included in the chapter are the Hardy-Weinberg Principle and the evolution involved in finite populations.

POPULATION EVOLUTION We have talked about evolution of individuals, which is actually a misnomer. Evolution does not happen specifically to individuals but actually happens in populations. As always, natural selection plays a major role in population evolution. It acts to promote traits that enhance survival of a species, while eliminating traits that do not support fitness of the species. Underlying evolution is mutations, which provide variation in the gene pool of a population. Genes will have several variants, called different alleles”. There can be more than one allele for a given trait or gene. In diploid organisms, there are generally two separate alleles for a given trait, which are stored on homologous or related genes and chromosomes. In polygenic traits, there can be many different combinations of alleles that make up the phenotype of the organism. Evolutionary study can expand these concepts to include the study of population genetics, which studies how forces in evolution can change the frequencies of certain alleles, genotypes, and phenotypes in the population. The allele or gene frequency is the rate of appearance of a specific allele. Behind every phenotypic change in the population is a change in the allele frequency. When this frequency change happens, it is said that evolution has occurred. Environmental factors can change the allele frequency because they affect natural selection, altering the species genetic makeup. If an allele affects the phenotype s fitness in a positive or negative way, this will change the frequency of an allele. Some alleles will be so beneficial that all organisms have the allele. The gene pool is the total of all of the alleles in a population.

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Genetic drift is the random change in allele frequency in a population. It usually occurs at the same time and because of pressure from natural selection. It may not always be possible to determine exactly what factors in evolution has played into genetic drift. The founder effect happens when a small number of individuals start a population, which is usually a small one. The founder effect can change the gene pool. Random drift can also occur because of mutations. A polymorphism is the expression of a different phenotype in a population of organisms. Polymorphic populations are those that have differing phenotypes. Population variation involves the differences in the phenotypes in a given population. It is based on the gene pool of the population and the environment. Genetic variance depends on the heritability of a trait. A trait like strong muscles from working out is an acquired phenotypic trait that is not inherited so it does not affect genetic variance. A heritable trait is able to be passed on to the next generation. Genetic variance is the diversity of the different alleles within the population. Genetic variations can be increased by decreasing inbreeding and increasing outbreeding. Large populations and low deleterious allele frequency will decrease the chance of a recessive allele from being inherited. Inbreeding depression involves the development of diseased offspring because of inbreeding. Genetic drift depends on genetic variance and on natural selection and selection pressures. There can be a variety of selection pressures that can contribute to this. Some genetic drift is completely random. An example is the change in allele frequency when some in the population have more offspring or when chance events change what happens in the mating process. Small populations have a greater chance of this happening, mostly because they are not buffered well against the effects of chance. We have talked about the bottleneck effect, which is usually from a natural disaster that wipes out a great portion of the population. This changes the genetic makeup of the survivors potentially, especially if the survivors have a different gene pool than the original population. The founder effect happens when a small number of individuals separate from the main population and when those that separate have a different gene pool from the original population. The gene pool becomes more representative of the few individuals that start up the new population. This is seen in certain, more isolated human populations in which mutations have existed in the founding members. Gene flow refers to the transfer of alleles into and out of a population, which is usually due to migration. Some populations will remain stable, while others will be in constant flux. Plants

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who send pollen to far-flung places will experience gene flow. Animals that travel long distances will have gene flow among their populations. Mutations are a driving force of diversity within a population. A buildup of mutations over time leads to the evolution of the species and is now new genes get introduced into the population. While most mutations are deleterious, some will be beneficial and will be selected for in the population. Mating in general is nonrandom, usually because of mate choice selection in the population. In assortative mating, there will be a preference given to a mate that is similar to the individual doing the selection. Physical location can also lead to pressures that lead to nonrandom mating in the population. The environment can affect the variation in the population. The sun itself can affect the pigmentation of the people living in it. There are also changes in some species in the gender of species created by the parents. Certain temperatures in amphibians, reptiles, and turtles can change the type of gender of the offspring. Geographic variation can also affect phenotypes. A cline is the phenomenon of gradual change in an environment along a gradient. This can be seen in differences in animal characteristics at the poles versus the equator. Mountain slope variations are an example of an altitude cline. Natural selection affects the entire individual and not just allele frequency. If a genotype both carries increased ability to have more offspring but leads to an increase in childhood death rates, this genotype will not be passed on because the combination is detrimental overall. This phenomenon is referred to as adaptive evolution. An organism s fitness can often be measured but it isn t the absolute fitness level that is as important as its fitness compared to others or relative fitness”. If natural selection favors an average of the phenotypes, this is called stabilizing selection. Mice who do not have extremes in coloration can better beat predators. Directional selection selects for those phenotypes that are more extreme. This is what happened to phenotypes of peppered moths that were extremely dark in industrialized areas. Diversifying selection leads to two or more dominant phenotypes—often present in the population for different reasons. Frequency-dependent selection favors either common or rare phenotypes. It depends on having different reproductive strategies for the different phenotypes. The favored phenotype depends on its frequency in the population.

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Sexual selection depends on sexual dimorphisms, which are differences in the male and female phenotypes. There is generally more variance in the reproductive success of the males rather than the females in some populations. This leads to competition among males for mates. Sexual selection involves the pressures on males and females to mate with another. Sexual characteristics do not necessarily lead to better survival of the male but will lead to greater reproductive success. This is what is seen in male peacocks that are at greater risk for predation and is called the handicap principle. The good genes hypothesis is involved in situations where certain phenotypic traits are associated with better genes and better overall fitness against things like low food supplies and predation. Both the good genes hypothesis and the handicap principle reflect honest signals to the female in order to affect her choice in mates.

HARDY-WEINBERG MODEL The Hardy-Weinberg Model describes what goes on in the genetic makeup of a population. It indicates that the allele frequencies and genotype frequencies in a population will be stable unless there are evolutionary pressures on the group. It assumes that there is no migration, no mutations, no emigration, and no natural selective pressures on a given genotype and assumes an infinite population. This basically does not work in the typical population but it can help to predict population changes in real populations. A population s genetic structure refers to the frequency of the different phenotypes rather than the frequency of the population s genes or alleles. If looking at the phenotypes, only the frequency of the homozygous recessive alleles can be determined because it is easily identifiable in the phenotype. This can be used to calculate the frequency of the remaining alleles and genotypes. There is a mathematical calculation that will determine how many of each allele there are in the population. Once the frequency of the recessive allele is known, the frequency of the dominant allele can be measured because the two frequencies add up to one. Things that will violate the Hardy-Weinberg Principle include non-random mating, the presence of mutations, gene flow in the population, natural selection, and finite population size, which leads to genetic drift. In a typical Hardy-Weinberg equilibrium, the population does not evolve. For true Hardy-Weinberg equilibrium, all of the alleles in the genome must stay at the same frequency.

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COOPERATION IN POPULATIONS Because natural selection favors certain organisms over others, one would think that this would lead only to selfish behavior in the species. This is, however, not the case, and cooperation is seen in many species. Within the organism itself, there are organelles that cooperate for the cell, genes that cooperate inside the genome, and cells in multicellular organizations that cooperate with one another. Between organisms, there are cooperative societies and cooperative breeding. Each population is filled with different actors that perform behaviors that go with or against the group. Altruism defines a behavior beneficial to a recipient but that costs the actor doing the behavior. Cheaters are those that do not cooperate or who do less than their share of the work for the population. Cooperation involves beneficial behavior that drives the evolution of the population. Some behaviors lead to direct fitness, which is the fitness an organism gains from producing offspring, while others lead to indirect fitness, which is fitness gained by aiding related individuals in the group. Kin selection involves the favoring of traits that directly benefit one s relatives. Inclusive fitness is the effect of behaviors on all members of the population. Mutualism is any type of two-way cooperation between members of the same or different species. Mutualism leads to a mutual benefit to both the actor and the recipient. The different members involved in a mutualistic relationship. There are certain genes an organism can have. The greenbeard gene is purely hypothetical gene that leads to a recognizable phenotype that is linked to a cooperative behavior in the individual. Without cooperation, natural selection would favor those who are selfish and who do not cooperate. Cheaters can have a specific trait that allows them to benefit from the other cooperators. It leads to higher fitness for the cheater, which would increase the frequency of the trait unless the frequency was so high that no one cooperated any more. Direct benefits and direct fitness favor mutually beneficial cooperation between members of the group, while indirect benefits help to explain why there is altruistic cooperation. Each act of cooperation may have differing levels of direct and indirect fitness. Indirect fitness is weighted by relatedness of the actor to the recipient. If both indirect and direct fitness is increased, the behavior is said to be mutually beneficial. In order for kin selection to work, there must be some mechanism for kin discrimination. Certain species of animals can tell who their kin is by certain vocal cues passed down from birds, for example, during the nesting period. When kin discrimination occurs, there is an increase in

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kin selection and closer relatives are benefited the most. Other kin discrimination factors include certain odors or certain phenotypes visible to relatives. Kin discrimination can be bad if it decreases the genetic variability in the population. Kin selection tends to keep populations close together so that relatives are near one another. This means that it would be less necessary to have kin discrimination because helping one s neighbors is likely to be the same thing as helping one s relatives. Neighbors are also likely to be relatives. Limited dispersal of organisms will usually favor cooperation but this isn t necessarily the case. This would be less likely to lead to cooperation if it means that the same relatives would have to compete for resources. Cooperation often has direct benefits to one s own offspring, leading to mutually beneficial behavior. Cooperation that increases population size could mean a decreased chance of getting eaten by predators. Cooperation can be enforced by punishing cheaters or rewarding cooperators. It does not have to be enforced if there is a shared benefit to cooperation. Meerkats can beat rival groups by cooperating to allow for a larger population. Cooperation in order to increase group size is called group augmentation”. It is beneficial for subordinates to cooperate even though they don t breed themselves. Cooperation is enforced by ejecting subordinate meerkats who themselves get pregnant. Enforcement of cooperation by rewarding cooperators and punishing cheaters is necessary sometimes because it increases the chance of cooperation. Ostracism is a typical punishment for cheaters.

GROUP LIVING Group living is when a species maintains some type of spatial proximity to one another. Group living is believed to have evolved after solitary living and happens in a species that gains an evolutionary advantage through group living. There is increased access to potential mates, increased ability to forage, increased protection against predators, and better access to social information. Groups can be heads, colonies, flocks, or other terms. Mixed species groups do exist in nature. Group living is hard to distinguish from solitary living and the end result is often an arbitrary definition. Sometimes, group living happens only during mating, the gathering or resources, or the raising of young. Group living does not have to be continuous for it to be present. It is not applied to things like moths that gather around lights or groups of animals that gather around a water source. There needs to be some type of social interaction.

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There are many genes involved in the development of group living. It also depends on ecological pressures and the environmental circumstances. Group living is partially a learned behavior in some species. There are some costs to group living. It increases the chance of passing on diseases to one member of a group to another as well as an increase in ectoparasites. It increases the competition between the species members who must compete for resources. Large group size can decrease reproductive success if there is competition among members of one gender for a mate. Group living can increase the biological stress on the individuals and there is an increased risk of inbreeding.

SOCIAL EVOLUTION Social evolution is the study of social progress from the past to the present and the study of which social characteristics are selected for or are preferable. Social progress is the attempt in a society to move toward a specific ideal. In humans, social evolution started in small groups and advanced to larger groups and cities. Western societies typically showed prejudice against women and non-white people, some of which still persists in these societies. Social evolution is, however, still occurring and is expected to change as modern society progresses.

EVOLUTION IN FINITE POPULATIONS As mentioned earlier, the Hardy-Weinberg principle falls apart in finite populations. In small populations, the effect of deleterious mutations is larger and beneficial mutations can be lost due to things like genetic drift. Fitness in the population will increase or decrease, depending on which of these types of mutations has a greater rate. Remember that there will generally be more deleterious mutations than beneficial ones but, if the population size is large enough, there will be an effect of beneficial mutations on the population. If a population is too small, genetic drift can surpass selection and adaptation so that the population s fitness designed. Genetic drift has a bigger influence in finite populations. This is because the frequency of certain alleles will more likely fluctuate over time so that mutations will have a greater effect on the population. Genetic drift does not favor heterozygosity of an allele. This means that there will be more individuals with a homozygous trait that will be either dominant or recessive. Genetic drift is completely random so that two separated populations that themselves are finite have a greater chance of later becoming divergent from one another.

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Population bottlenecks for whatever reason cause a temporary reduction in numbers of the population. This is going to accelerate genetic drift and will change the allele frequency to a greater degree. Some populations will break off to develop on islands or otherwise isolated from the parent population. The founder effect will increase the chances of divergence of these populations. Because most mutations are neutral, they will lead to genetic drift and will help the progress of evolution in a finite population. The rate of mutations will then determine how fast a population evolves. Molecular clock theory can be used to help identify ancestors and can approximate the time when a population first developed a specific mutation.

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KEY TAKEAWAYS •

Populations have a certain gene pool that each of the members draw from.

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Evolution acts on populations rather than on individuals.

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The Hardy-Weinberg Principle depends on a finite population, no mutations, no migration, and no genetic drift.

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Cooperation can improve the state of a population even though competition and natural selection would seem to favor those that are selfish.

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Group living has benefits and costs but for some species, the benefits outweigh the costs.

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In finite populations, there is greater genetic drift, a greater chance of a decline in fitness, and a loss of the frequency of heterozygosity.

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QUIZ 1. Forces in evolution can change the frequency of each of these things in a population except for what? a. Alleles b. Genotypes c. Phenotypes d. Genomes Answer: d. Genomes is a concept that is defined as the totality of the genes in an organism. The frequency of genomes does not change but the alleles, genotypes, and phenotypes will change in frequency in the genome of members of the population. 2. What is the earliest change in a population that has suggested that evolution has occurred? a. Change in habitat b. Change in an allele frequency c. Change in gender frequencies d. Change in the population size Answer: b. A change in the frequency of an allele is most likely to be the earliest evidence that evolution has occurred within the population. 3. What is the main cause of a population bottleneck? a. Separation of the population b. A natural disaster c. A sudden increase in the population d. Increased inbreeding in a population Answer: b. Most population bottlenecks are caused by a natural disaster that kills off most of the population so that the gene pool of the surviving population is different from the gene pool of the original population.

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4. What is not the main cause of the founder effect in a population? a. Separation of the population b. Decrease in natural selection c. A sudden decrease in the population d. Increased inbreeding in a population Answer: b. Each of these is a causative factor in the founder effect in a population except that it isn t caused by a decrease in natural selection. 5. What is not assumed by the Hardy-Weinberg Principle? a. No migrations b. No mutations c. No selective pressure d. Finite population Answer: d. Each of these is assumed as part of the Hardy-Weinberg Principle except that it assumes an infinite population rather than a finite population. 6. What is least likely to violate the Hardy-Weinberg Principle? a. Population gene flow b. Low allele frequency c. Non-random mating d. Mutations Answer: b. The Hardy-Weinberg principle is violated in each of these circumstances but it is not violated if there is a low allele frequency.

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7. An individual in a cooperative environment who does not do his or her own share of the work is called what? a. Mimicker b. Misfit c. Parasite d. Cheater Answer: d. A cheater is an individual in a cooperative environment who does not do his or her own share of the work in the group. 8. What is not true of a greenbeard gene? a. It leads to selfish behavior. b. It has an identifiable phenotype. c. It is linked to cooperative behavior. d. It is largely hypothetical. Answer: a. A greenbeard gene is a hypothetical gene that has an identifiable phenotype that is known to be linked to cooperative behavior. 9. What is not necessary to define group living? a. Social interaction between group members b. Spatial proximity for some period of time c. Competition for resources d. At least two individuals in the group Answer: c. Each of these is necessary to define group living except for competition for resources, which is not a part of the definition.

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10. What is not an advantage but is instead a cost of group living? a. Increased risk of disease b. Decreased cooperation c. Increased biological stress d. Increased chance for inbreeding Answer: b. Each of these is a cost of group living except that it does not necessarily decrease cooperation among the members.

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CHAPTER TWELVE: COEVOLUTION This chapter focuses on the subject of coevolution. Coevolution is a phenomenon that happens when two or more species affect each other s evolutionary processes. This can happen when two species have a mutualistic relationship or when there is a host-parasite relationship. There are two other types of coevolution discussed in this chapter, including antagonistic coevolution and mosaic coevolution, which involve specialized relationships between two or more species.

COEVOLUTION EXPLAINED Coevolution can be explained as an evolutionary process in which two or more species affect each other s evolution in some way. This phenomenon was described by Charles Darwin, who studied the evolutionary relationships between certain insects and flowering plants. Coevolution is particularly important in understanding how ecological communities operate. Part of the process involves the exertion of selective pressures of one organism on the evolution of another. Coevolution can be pairwise or specific, meaning that exactly two species are involved; it can be guild or diffuse evolution, involving the coevolution of several species at the same time. Coevolution sometimes leads to a mutualistic relationship between two or more species. An example of this is the relationship between flowering plants and insects. Honeybees, for example, use nectar from flowering plants and also collect pollen for dispersal to other plants. These groups have coevolved over the last 100 years. The same relationship exists with certain plants and butterflies, wasps, ants, beetles, and flies. How it works is that flowers can communicate with the pollinators due to their scent. The insects use the flower s scent to tell where the plant is located and how far away it is. There are also patterns of stripes and colors that lead the insect to the nectar/pollen combination. Insect pollinators are blue in color, while bird pollinated flowers are other red or orange. Lastly, some orchids have parts that mimic the females of certain insects so that the males will copulate with them. This is called entomophily. Another relationship involving coevolution is ornithophily, which involves the relationship between pollinating birds and certain flowers. This is the case with hummingbirds and their ornithophilous flowers. The birds use the nectar as their main source of food and both the flower s color and shape fit that of the hummingbirds. The flowers have evolved so they bloom

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when the hummingbirds are breeding. The flowers are more ornate than insect-pollinating flowers. Most likely, the flowers evolved to be mutualistic with insects but later became mutualistic with birds. These flowers have more nectar and produce more sugar than entomophilous flowers; they have tubular shapes that encourage pollination by the bird species. As mentioned, the coloration tends to be red but some can be ultraviolet. Other examples include figs and fig wasps that pollinate the fig and acacias and acacia ants, which involves protection of the acacias from predators in exchange for nourishment and shelter. There can also be coevolution of hosts and parasites, which is the case particularly with viruses, which are obligate parasites that cannot survive without a host. This is somewhat of an arms race so that, if either the host or parasite is unable to keep up with the other, the one that cannot keep up will be eliminated. In other words, if the virus cannot engage with the host, it will not survive. On the other hand, if the virus is too aggressive and kills the hosts completely, both the virus and host will die off. The relationship between hosts and parasites likely drove the evolutionary progress of sexual reproduction so that organisms could create an offspring that was more efficient at fighting off the parasite. This was considered an evolutionary advantage over asexual reproduction. The problem is that the parasite will often coevolve to be parasitic to the offspring to some degree. There is the phenomenon of brood parasites in which cuckoo birds evolved to lay their eggs in a competitor s nest by killing the eggs or young of the host bird. The eggs look like the original bird s eggs so the young are raised by the host bird. They have evolved to have thicker eggshells and a shorter incubation time so that the eggs hatch sooner than the host s eggs. There is coevolution of predators and prey. The prey evolves in order to escape the predator and the predator evolves to be better at catching the prey. There are selective pressures placed on both species. In other situations, there is coevolution of plants and the animals who eat them. Plants will evolve to be better able to have their seeds not get eaten and the animals get better at getting at plant seeds for food. Coevolution that crosses more than two species is called diffuse or guild coevolution. This is the case with certain flowering plants that coevolve with more than one species of insects. In some cases, flies, bees, and beetles form a guild that together pollinate flowers that have nectar. There is a phenomenon called an evolutionary arms race, which is a struggle between sets of coevolving genes that compete with one another in order to adapt and counter-adapt to one

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another. This can happen between predators and their prey or between a parasite and its host. Members of the same species can also have an arms race with one another. An arms race can be symmetrical or asymmetrical. If it is symmetrical, the selection pressure to the different species is in the same direction. An example of this phenomenon is seen in trees that develop increases in height in order to out-compete each other for available sunlight. If this is asymmetrical, there are opposite selective pressures, where prey learns to be faster and cheetahs evolve to be stronger hunters. There is a host-parasite coevolution that involves selective pressure between the two species. They have an antagonistic relationship so that the pathogen gets more infective and the host gets more resistant. Offspring of the host evolve to get better at resisting the host and the offspring of the parasite gets better at becoming more virulent. There is a continual adaptation over time with each species in order to avoid extinction, which is called the Red Queen Hypothesis. Bats and moths have coevolved in an evolutionary arms race. Bats catch their prey through echolocation. Moths can detect echolocation and have evolved to be more evasive in their flight patterns. They can also confuse the echolocation process by making their own clicking sounds and jam sonar signals. The same moth can use all these defense mechanisms. Bats have evolved to use clicks that the moths cannot hear. There is also an arms race between newts and garter snakes. The newts emit a powerful tetrodotoxin, which is a nerve toxin to fight predators. Common garter snakes are resistant to the toxin because they can prevent the binding of the toxin in the snake nerve cells. This favors newts that have the ability to make more toxin. In turn, the snakes develop a better resistance pattern. This has led to newts making much more toxins necessary to destroy any other predator besides the garter snake. There are floodplain death adders that kill three different types of frogs, only one of which is highly toxic. In order to survive, the adders wait to consume their prey because this detoxifies the deadly frogs. They take their time also so they can eject the toxic frogs while consuming the nontoxic frogs. Frogs adapt by producing more toxin per frog. In some cases, species have been introduced to an environment that did not have the time to adapt to them. There are places where cane toads and rabbits have been introduced. Without competition, they have overrun the environment so that indigenous species became endangered or extinct. This is what happened with the dodo bird, who died off because of predation by

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humans, destruction of their habitat, and predation by introduced species to the island they lived on.

COEVOLUTION AND MUTUALISM With mutualism, there is an ecological interaction between at least two organism types that is beneficial to both species. Mutualism is actually the most common interaction between two species. It happens in all types of organisms, including flowering plants and pollinators, the dispersal of plants by animals, and the interaction between mycorrhizal organisms and vascular plants. The relationship increases the fitness of both species, which is different from interspecies competition, which decreases the fitness of both species. It is also different from parasitism and exploitation, which decreases the fitness of one species. There are differences between mutualism, cooperation, and symbiosis. Cooperation increases the fitness of the organisms that share the same species; symbiosis is a broader term that can include commensal relationships, mutualistic relationships, and parasitic relationships. Mutualism is a factor in the growth of about 48 percent of land plants because of mycorrhizal relationships. Mycorrhiza are fungi that provide phosphate and nitrogen to the plant in exchange for carbohydrates. Many mutualistic relationships are called service-resource relationships. This is what happens with flowers and pollinating species, cleaning symbiosis, and zoochory. In cleaning symbiosis, one species gets rid of pests on certain species in exchange for the nutrients that come from the pests. In zoochory, there is the dispersal of seeds by animals, which is similar to pollination. A miscellaneous category is the protection by ants of aphids. The ants live off the sugar on the aphids and give predator defense for the aphids. A service-service relationship is what happens between clownfish and sea anemones. The fish will drive off predators and the anemone s have tentacles that also protect the fish from predators. These relationships are not common. The other aspect of this is that the fish secrete ammonia that is used by the sea anemone for food. These types of mutualistic relationships exist everywhere on earth. This is true of plants and their pollinators in different parts of the world. When conditions get harsh, the relationships break down. When one species reaches a critically low level or suffers a major insult to a significant degree, a critical point is reached and both organisms collapse, with the potential to

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become extinct. The organisms can survive if their numbers increase so the relationship can be sustained. Humans also have mutualistic relationships. The flora in the gut is necessary for efficient digestion of nutrients. Head lice in humans reduces the threat of lethal diseases from body lice. Domesticated animals and plants rely on humans for propagation and humans use these organisms for food. Bean plants grow on corn stalks and provide nitrogen for the soil plants. Mutualism is not a static event and can shift by evolutionary processes. The relationship can switch to parasitism; one partner can become autonomous; one partner may become extinct, which can lead to the extinction of the other; and one partner will switch to have a different mutualistic species partner.

HOST-PARASITE COEVOLUTION Host-parasite relationships, as we discussed, also involve coevolution. There is reciprocal selective pressure that helps to maintain the relationship and allows for evolution to continue. There are several reasons for these relationships. One thing you need to know is that increased virulence of the parasite can be detrimental to the parasite because the parasite might kill off the host too quickly, practically ensuring that the host cannot help to transmit the organism to others. Because of reciprocal selective pressures, there can be rapid adaptation of both species. Based on the Red Queen Hypothesis, each species must evolve and adapt in response to the adaptations of the opposite species. With the host-parasite relationship, there are always changes in allele frequencies in the environment. The parasite must adapt to the most common genotype of the host so that it can affect the largest number of hosts. Rare host genotypes are then selected for so it becomes more common. When this happens, the parasite adapts to this new, more common genotype. This can happen quickly over just a few generations and favors uncommon alleles. Overdominance can happen if the heterozygote is more advantageous than the homozygotes. This happens with sickle cell anemia. The homozygotes for this disease have an increased risk of death, while the homozygous normal person has an increased risk of getting malaria. This favors the dominance of the heterozygote, called heterozygote advantage, in areas where there is malaria.

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Because of the Red Queen Hypothesis, certain species that can reproduce sexually and asexually will choose sexual reproduction when there are parasites are present. This is true of certain shell-bearing snails that get parasitized by trematodes. If there are parasites, there is an advantage to doing sexual reproduction because the offspring might be better fit to fight off the parasite. The Red Queen hypothesis was named after Lewis Carroll s story in which there was constant running, even though there was no increase in actual distance covered.

ANTAGONISTIC COEVOLUTION Antagonistic coevolution involves the relationships between males and females of a species so that there are changes in sexual structures to counteract those of the opposite sex in order to have maximal reproductive success. Male mating behavior is often detrimental to the female s fitness, particularly in those species that have traumatic insemination. Females must change in order to maintain reproductive success. This is what happens in certain insects that, if their thoraxes are inseminated too many times, they will die. Many female insects will be damaged by frequent male inseminations so those that survive can reproduce. Females have a spermatheca or pseudo-spermatheca that play a role in sperm storage. Females can use the stored sperm to inseminate themselves when the circumstances are optimal. Not all sperm get used for insemination and some get expelled. Females also have enzymes that break down seminal fluid in order to select the sperm to be chosen. Females can also be evasive and will fend off insemination attacks. Males have developed spiny genitalia that will help anchor them during copulation. This can scar the female reproductive tract so females have developed thicker copulatory tracts. Males have also developed a method to inseminate the female abdomen directly. This is called traumatic insemination. Females have evolved to phagocytize or kill the sperm cells. Males will develop a longer sperm tail length because the females seem to prefer this particular trait. There is no other evolutionary reason known for this evolutionary tail length discrepancy.

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MOSAIC COEVOLUTION Mosaic coevolution is a process that uses community ecology and geographic location in order to shape the coevolution between species that interact with one another in more than one population. There are hot spots that involve strong reciprocal selection with one another, while cold spots do not have this issue. Flowers will adapt their shape to be more mutualistic to the shape of the pollinator s proboscis. The degree to which this is done depends on the geographical area being looked at. Prey will constantly adapt to be faster or more evasive depending on what factors affect the predator s abilities. Certain plant species will have variable seed toughness in certain geographical areas in order to be more resistant to seed predators.

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KEY TAKEAWAYS •

Coevolution can involve two species or several species together.

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Mutualism involves the coevolution of species so they can better have a mutualistic relationship.

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The parasite-host relationship often involves an evolutionary arms race, in which the species try to out-evolve each other in order to get into or out of the relationship.

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The Red Queen Hypothesis refers to the coevolution of parasites and hosts.

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Predators and prey coevolve in order to become better at either catching the prey or escaping the predator.

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The introduction of foreign species can wipe out indigenous populations because of a lack of competition.

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Mosaic coevolution involves the process of evolutionary changes that differ in different geographical areas.

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QUIZ 1. What is coevolution referred to when it involves just two species evolving with each other? a. Guild coevolution b. Diffuse coevolution c. Parasitic coevolution d. Specific coevolution Answer: d. Specific coevolution or pairwise evolution is the evolution together of just two species with each other. 2. What other species of organisms is mutualistic and has coevolved with honeybees? a. Ferns b. Flowering plants c. Mosquitos d. Deciduous trees Answer: b. Honeybees have evolved together with flowering plants because they have developed a mutualistic relationship with one another. 3. What happens if a virus is too aggressive to humans and kills the hosts entirely? a. The viruses will become overpopulated in the world. b. The viruses will die off for lack of hosts. c. The viruses will eventually mutate to be less infectious. d. The viruses will occupy a different host. Answer: b. If a virus is too virulent or aggressive so that they kill off the hosts, they will not generally be able to mutate fast enough to find another host and will die off themselves. They do not have the ability to survive long outside the host and cannot overpopulate the earth.

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4. What is the major evolutionary contribution of the coevolution of hosts and parasites? a. The development of sexual reproduction b. The development of the innate immune system c. The development of the adaptive immune system d. The development of mutualism between two species Answer: a. It is believed that sexual reproduction developed in evolution because of host-parasite relationships that allowed for the better ability to fight off parasitic disease by the host s offspring. 5. What are moths least likely to do in order to avoid getting eaten by bats? a. They have erratic flight patterns when there is echolocation. b. They make their own clicking sounds to confuse echolocation. c. They jam sonar signaling. d. They have evolved thin wings that cannot be picked up through echolocation. Answer: d. The moths do each of these things to confuse the bats but they do not have thin wings that cannot be picked up through echolocation. 6. Which is an example of a mutualistic relationship between two organisms? a. Honeybees and flowering plants b. Cheetahs and gazelles c. Snakes and mice d. Moths and bats Answer: a. The relationship between honeybees and flowering plants is mutualistic because both members benefit from the relationship. The rest of the relationships are predator-prey relationships.

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7. The dispersal of seeds by animals in nature is referred to as what? a. Zoochory b. Cleaning symbiosis c. Service-resource symbiosis d. Parasite-host relationship Answer: a. Zoochory is when seeds are eaten by animals or when fruit is eaten by animals, who then pass on the seeds through dispersal in the environment. 8. What is an example of a service-service symbiotic relationship? a. A parasite provides disease resistance to the host b. Two species protect each other from predators c. An organism secretes a substance that is taken up by the host organism d. A predator is prevented from eating all of the animals in a herd Answer: b. When two species protect each other from predators, this is called a service-service symbiotic relationship. The relationship between clownfish and sea anemones is like this. 9. Which disease state has a heterozygote advantage in certain populations? a. Muscular dystrophy b. Cystic fibrosis c. Myasthenia gravis d. Sickle cell anemia Answer: d. Patients with sickle cell anemia have a heterozygote advantage because being a heterozygote will confer resistance to malaria, which is not the case with homozygotes.

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10. What two organisms coevolve in antagonistic coevolution? a. Parasites and hosts b. Males and females of the same species c. Competing species who use the same resources d. Mutualistic species Answer: b. Males and females of the same species will have antagonistic coevolution with each other.

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CHAPTER THIRTEEN: EVOLUTION AND DISEASE The focus of this chapter is evolution and disease. Diseases affecting all species have been around since the beginning of time. The way in which diseases have originated is discussed in this chapter, including how some human diseases have crossed species to affect humans. Also covered in the chapter is the evolution of senescence or aging. There are several theories as to how and why humans age, which are discussed in the chapter.

EVOLUTION OF DISEASE ORIGINS There are some apparent flaws in the human body that can be explained by evolution. Certain things, like fever, cough, vomiting, and pain are actually defense mechanisms that have evolved over time. Other diseases, like those from viruses or E. coli, are just facts of life because we interact with other organisms. Third, lifestyle diseases such as those caused by too much dietary fat have happened so recently in evolutionary time that humans have not kept up with the change. Finally, diseases like sickle cell anemia are evolutionary tradeoffs that have some sort of benefit to humans so they persist as diseases. Coughing is an evolved defense because it clears out infection before it can become pneumonia. The ability to feel pain is also a defense mechanism because it warns the body of danger. People who cannot feel pain die young from damage to tissues or from infections. Even things like sneezing, anxiety, fatigue, diarrhea, vomiting, and nausea are defenses. Fever can facilitate the destruction of pathogens and is evolutionarily controlled. Animals that cannot raise their own body temperature will move to a warmer area when infected. Anemia from low blood iron in chronic infections is an adaptive mechanism. Iron is retained by the liver to stop bacteria from gaining access to this substance. Morning sickness is also defensive because it prevents women from eating things that could be toxic to the fetus. Anxiety is a defense mechanism that prevents animals from getting too close to predators. Diarrhea and fever are so beneficial that treating them can be harmful to the body. Even treating morning sickness could have the added disservice of leading to unrestricted eating that leads to birth defects. Humans are in natural conflicts with other organisms that are pathogenic to us. Some of the problem is the rapid evolution of microorganisms compared to humans. Pathogens that cannot

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defend themselves quickly become extinct. At one time, doctors believed that vaccines and antibiotics could eradicate infectious diseases. The problem is that pathogens can all evolve rapidly and antibiotic resistance is a big problem. Resistance can even jump to different species. While too much virulence can kill the host and the pathogen too, this doesn t mean that organisms will automatically become less virulent. Humans are also coping with the relatively new arrival of things like dietary fat that has contributed to atherosclerosis. This has greatly increased in prevalence in the last century. Exercise, vegetable-eating, and low-fat intake can prevent heart attacks but most people do not follow these practices. More and more people are becoming obese, which is a contributing factor to many diseases. Some of this is evolutionary because the tendency to like things that aren t good for us was bred into societies where these things were rare and competed for. There is also an easier access to alcohol, drugs, and alcohol, which causes a large number of diseases and death. The desire for psychoactive drugs is an old one but the availability of newer and stronger drugs has become a much bigger problem. Some drugs, like nicotine, codeine, and cocaine, evolved to protect certain plants from insects but they affect our nervous system as well. Every person is evolutionarily wired to become addicted to these drugs. The rise in breast cancer is from changes in modern society. In non-modern societies, menarche starts late and breastfeeding prevents hormones from affecting the breasts. It is believed that having a great many menstrual cycles contributes to getting breast cancer. There are some evolutionary tradeoffs we humans have had to make. Good hearing would be nice but would be very distracting. Stronger bones would prevent breakage but the need for calcium would be too great. The sickle cell trait has an evolutionary benefit in malaria-prone countries but this is traded off for disease in those individuals who have sickle cell anemia. Humans have a long history of acquiring zoonotic diseases, which are infectious diseases gotten from animals. About 60 percent of human diseases ultimately came from animals. There are some apparently new diseases, such as Ebola, Zika virus, and SARS that are actually not new. They have become apparent because of new agricultural practices, changes in population demography, and areas where there is a lack of health services. These take a small spillover outbreak and turn them into major epidemics. Ebola is carried by fruit bats but has infected antelope and primates. Eating certain animals has led to human Ebola disease. Contact with bodily fluids in humans who have Ebola passes the

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disease to other humans, particularly when caring for the sick or burying the dead. Population overgrowth, eating of livestock, and clearing of the land contributed to the outbreaks we ve had. SARS or severe acute respiratory syndrome is a 21st century disease from a type of coronavirus. It was originally in China and was found originally in bats but later infected civet cats. Civet cats were eaten in China, where it originated. The disease was passed in open live animal markets. Zika virus is another relatively new viral infection first isolated in rhesus monkeys back in 1947. It gets to humans through mosquito bites. While it has been around for a while, it has become more popularized by the birth defects it causes in pregnant women who get it. It is not infectious outside of mosquito bites.

DISEASE SUSCEPTIBILITY Infectious diseases are strongly influenced by genetics. Infections that reduce a human s reproductive potential will drive selection toward individuals that are more resistant to disease. Selection is more likely to be seen in diseases that have been around humans for a long period of time. Some pathogens cause sudden diseases but, if survived, have little consequences. Others have the risk of chronic infections and fertility impairment. Evolutionarily-speaking, malaria is one of the oldest human diseases. This was later followed by tuberculosis, smallpox, leprosy, cholera, and most recently, HIV disease. These diseases spread with migration patterns that have happened over time and many originated in Africa. Modern medical practices have significantly decreased the risk of all of these diseases. Doctors and researchers have studied the genetic susceptibility to certain infectious diseases. The goal is to identify better medications and vaccines that can reduce the incidence of disease. One recent finding, for example, is a genetic marker in some Europeans that result in a decreased risk off HIV disease. This led to new drugs to fight the disease. In addition, there are those that are resistant to malaria, who are being studied to find a vaccine against the disease. Doctors are also using genetics to target vaccines to children who would be most susceptible to the disease. The risk for disease susceptibility in infectious diseases is genetically-related. There are certain families that have a great risk of infectious diseases. Twin studies on identical and fraternal twins have been done looking at disease resistance. Several chronic infectious diseases, such as leprosy, tuberculosis, and chronic hepatitis B are controlled through inheritance. The difficulty

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is studying these and other diseases in terms of genetics is that the human genome is large and it is laborious to look at the entire genomes of many people in order to find the necessary trends. Still, there are some diseases that have been linked to certain genes in humans. An example of this is the presence of sickle cell gene and malaria resistance. People who have the Duffy blood group or Melanesian ovalocytosis also have protection against malaria. People with a prion protein gene variant are protected from Creutzfeldt-Jakob disease and those with a CCchemokine receptor 5 mutation do not get HIV-1 disease to a great degree. Being a blood group non-secretor protects against Norwalk viral infections. There is some evidence that there are genes affecting the innate immune system that confer a decreased risk to a number of infectious diseases, particularly if the person is heterozygous for the genes. Most of the diseases that have been studied are chronic diseases like malaria, tuberculosis, and leprosy. Related to this is the finding of certain genes that increase the risk of autoimmune diseases, particularly in European populations.

HOST AND PATHOGEN EVOLUTION A pathogen thrives if it can survive, reproduce, and spread to a different host. Parasites, host immunity, predators, and limitations in the environment all exert evolutionary pressures on the survivability of a particular pathogen. We have already talked about the evolutionary arms race, in which the pathogen and host continually adapt in order to outdo each other. The hosts that have resistance are selected for and the pathogen that can successfully beat those resistances are also selected for. There are physical barriers that first protect the host from disease. Pathogens have evolved to have toxins and enzymes that can break through these defenses. Host complement systems also protect the host but there are enzymes in the bacterial species that can get through these defenses as well. Other defense mechanisms include sequestering host resources, such as iron, which is sequestered in the liver, lymph cells in the immune system, and antibiotics made by the host that can fight off disease. The previous chapter on coevolution explained how it is coevolution that causes the changes in the host and pathogen over time so that both the host and pathogen can survive. Because it takes much longer for human and higher animal evolution to occur compared to that of bacterial and viral organisms, mankind has augmented the lack of evolution through the invention of

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antibiotics and other interventions that put added pressure on the organisms. Bacteria also compete with one another, which affects the pathogen genetics. As mentioned, bacteria must first overcome the innate immune system. This largely means overcoming barrier systems but it also must overcome the inflammatory responses in humans as well as the cells that indiscriminately kill off pathogens without the need for antibody responses. Humans use competition between healthy bacteria on the skin and in the GI tract that prevent pathogens from taking hold. Mucus and the blood-brain barrier keep pathogens out of delicate areas of the body. Some bacteria make enzymes that break down mucus to ensure a greater chance of infection. Other pathogens target areas of the GI tract that have less mucus. There are bacteria that break the cell to cell junctions and bacteria that break up the protective skin barriers. Humans have a way to sequester iron needed by microorganisms. This has led to the evolution of organisms that can scavenge for iron as part of their pathogenicity. There are also bacteria that steal iron from human proteins. The greatest selective pressure that pathogens have placed on humans in gaining the advantage in diseases is the development of antibiotic resistance. It can happen very quickly and can cross to different species of bacteria. Bacteria have evolved to expel antibiotics, avoid attaching to antibiotics, and inactivate antibiotics. A big problem now is the development of multi-drug resistance. Less effective but still a problem is the elimination of rival bacteria by secreting toxic proteins that kill beneficial bacteria.

EVOLUTION OF SENESCENCE As an organism ages, their ability to function, fight off disease, and succeed reproductively goes down. All organisms die at some point and there are several hypotheses as to how this occurs. It was originally believed that aging was a mechanism of making way for the next generation as a necessary part of evolution. This theory has largely been discarded since the beginning of the 20th century. Another theory is that aging is a matter of neglect because of the highly competitive aspect of life on earth. Animals in the wild die from predation, accidents or disease; this lowers the average age at the time of death. It means that there is no evolutionary advantage to being fit as an older organism.

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The theory depends on the idea that there are random mutations that accumulate over time, leading to the damage seen in older individuals. While this may be true, there are scientific reasons why this might not completely explain senescence and death. Since then, there has been the theory of antagonistic pleiotropy, which means that one single mutation can have both beneficial and deleterious effects on the host. The idea is that having certain genes is beneficial early in life but becomes damaging to the host later in life. This is the theory that exists today but it is mostly the prevailing theory because a better theory has not been discovered. If it was entirely true, breeding animals for long life would mean they would have reduced reproduction but actually the opposite has been found to be true. Another theory is called the disposable soma theory, which means that excess energy is spent in old age for repair of the body, leading to a lack of energy available for maintenance so the body deteriorates. This theory depends on limited resources available to the organism. The problem with this is that organisms faced with calorie restriction actually live longer than those with more resources. Still another theory is that DNA damage is the main cause of aging. The ability to repair DNA decreases when cells are not dividing as much, which would lead to more DNA damage. This further leads to a loss of tissue and cell function over time. Free radicals are believed to be behind the destruction of the DNA and the cell. Organisms that use oxygen to the greatest degree as part of metabolism will die faster. A final theory is that there is programmed cell death for all cells. Species that live longer can offset the damage caused by free radicals, oxidation, and the shortening of end segments called telomeres on DNA fragments. Organisms that reach sexual maturity earlier are less likely to be able to repair damaged DNA so they have a shorter lifespan. There are theories about natural selection that may help to explain aging. Remember that evolution acts on populations and not on individuals so that populations that survive better as a whole will live longer if it is beneficial. In species where older post-reproductive members of the population help to raise the young, these species have a longer lifespan. This is true for dolphins and pilot whales. Evolution necessitates the death of aged species so that they die off rather than dominate the gene pool. If too many older organisms contribute to the gene pool, the population will not evolve to its greatest degree. In this case, evolvability itself contributes to senescence.

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There are two kinds of mortality. Intrinsic mortality is aging due to internal factors, while extrinsic mortality is aging due to environmental factors. Organisms with less predators have a greater degree of intrinsic mortality, while organisms with a lot of predators have a greater degree of extrinsic mortality. Predatory animals live longer than prey animals. Humans have a lower intrinsic mortality because their intelligence has helped to overcome it. There are a couple of diseases that are related to accelerated senescence and death. Progeria is a single-gene disease that accelerates aging in childhood so that they die early in life. Werner syndrome is another single-gene disease that prevents growth at puberty and an early onset of death in the person s twenties or thirties.

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KEY TAKEAWAYS •

There are many reasons that diseases occur that have evolutionary mechanisms.

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Pathogens and hosts have evolved together in an evolutionary arms race.

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Humans have specific defense mechanisms that many pathogens can overcome.

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The biggest pathogenic response to host defenses is the development of antibiotic resistance.

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There are many unproven theories behind the aging process.

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There are intrinsic and extrinsic factors that play into mortality.

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QUIZ 1. What evolutionary phenomenon is not a defense mechanism that helps to clear pathogens? a. Fever b. Cough c. Diarrhea d. Pain Answer: d. Each of these defense mechanisms has evolved to clear pathogens more easily, except for pain, which instead acts as a warning system that something has gone wrong in the body. 2. What is the evolutionary benefit of morning sickness? a. It expels toxic substances from the body. b. It restricts the eating of potentially toxic substances. c. It is a side effect of having high human chorionic gonadotropin levels. d. There is no evolutionary benefit to this phenomenon. Answer: b. Morning sickness is believed to prevent birth defects by restricting the access to potentially toxic substances in the diet. 3. Which drug did not originally evolve as a protective mechanism for plants against insect infestation? a. Nicotine b. LSD c. Opium d. Cocaine Answer: b. Each of these is a protective mechanism that protect plants against disease from insects but they happen to affect the human nervous system as well.

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4. What is a zoonotic disease? a. A disease that only exists in animals but not humans. b. A disease that mimics a related disease in animals. c. A disease that does not kill animals but kills humans. d. A human disease that was once found only in animals. Answer: d. A zoonotic disease is a human disease that was once found only in animals but crossed species to infect humans. 5. What animal did SARS get transferred from to humans? a. Civet cats b. Rats c. Opossums d. Cattle Answer: a. SARS was originally transferred to people in China who ate civet cats as a delicacy. It is believed that civet cats got the disease from bats. 6. What was the original species to have the Zika virus infection? a. Insects b. Monkeys c. Antelope d. Koala bears Answer: b. The virus was first seen in rhesus monkeys but is passed in humans through the bite of an infected mosquito. 7. Which infectious disease has not had a known resistance gene associated with protection against it? a. SARS b. Malaria c. HIV d. Norwalk virus

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Answer: a. Each of these has been linked to something genetic that protects a person against getting it except for SARS, which does not have a protective gene associated with it. 8. What is the first defense that humans have against bacterial and viral diseases? a. Adaptive immune system b. Antibody responses c. Antibiotic proteins d. Barriers to pathogens Answer: d. Barrier systems are the first line of defense against bacterial and viral infections. The pathogens, however, have found ways to counteract these mechanisms. 9. What is the biggest evolutionary selective pressure that bacteria have done to gain a foothold in human pathogenicity? a. Antibiotic resistance b. Elimination of bacterial competitors c. Iron scavenging capabilities d. Enzymes that break down barriers Answer: a. Each of these plays a role in giving bacteria the advantage over mankind but antibiotic resistance has played the greatest role. 10. What theory has been proven to be the cause of senescence and dying? a. Reallocation of caloric resources for repair rather than the organism’s maintenance. b. There is a buildup of DNA damage that causes cell function to decline. c. There is an accumulation of mutations that lead to cell death. d. There is no proven theory on senescence and aging. Answer: d. There are many theories on senescence and dying but none of these has been scientifically proven to be truer than any other theory.

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CHAPTER FOURTEEN: FUTURE OF EVOLUTION This chapter looks at the future of evolution, particularly of humans and of the planet itself. We will talk about what s already happened with the Holocene extinction, often called the sixth mass extinction event on earth. Exactly how humans will evolve is unknown but scientists can make some speculations, which are discussed in the chapter. Human extinction is covered as a possibility as is the future of the planet with the progress of global warming, which will affect the earth itself and the humans on it.

HOLOCENE EXTINCTION The Holocene extinction is believed to be a type of mass extinction event. Anytime 75 percent of the species are eradicated in a short period of time, this is considered a mass extinction event. There is no clear definition of when the Holocene extinction began, which is also referred to as the anthropogenic extinction event because it is human-caused. Some say it started as soon as humans left Africa about 160,000 years ago. Man is considered a predator that, through hunting and foraging, has destroyed many species. The rate of extinction in current times is between 100 and 1000 times greater than what would be expected with background extinction. It is expected to be 10,000 times greater in the near future, according to some forecasters. Losses have occurred through overconsumption, destruction of habitats, or the direct elimination of species that humans see as threatening. Because the extinction in species has been based on human activities, it is also called the Anthropocene extinction. This may actually be separate from the Holocene extinction because it is believed to have started in the middle of the 20th century. This is when the Industrial Revolution began. Others believe that human intervention on extinction did not occur until about 12,000 years ago. This was a time of increased human population numbers and was linked to the start of overconsumption of other species. Habitat destruction has occurred mainly through agriculture but overfishing and the devastation of the oceans also play a role. Pastures make up a quarter of land—taking up the largest percentage of land. These areas do not support wildlife; these have contributed the most to loss of wildlife species.

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Humans have contributed to loss of species through pollution, transmission of infectious diseases, hunting, deforestation, crop introduction, and domestication of animals. Certain plants and animals that have become food for humans have also led to species extinction. Humans are apex predators. There were species of large animals in places like Madagascar and New Zealand that do not exist. Now most larger species are found in Africa, while smaller numbers are found in Australia. The loss of these megafauna in South America has happened but it is not believed to have happened because of humans. Since humans have arrived, more than 80 percent of large animals and larger marine animals have become extinct. Most of the biomass of mammals is currently made of livestock, followed by humans and wild animals. Seventy percent of birds are domestic birds. There are human factors that have risen the concentrations of methane and carbon dioxide, which are greenhouse gases. Most of the problem is due to deforestation practices or agricultural development. This actually started thousands of years ago before the Industrial Revolution. Carbon dioxide levels began to increase 8000 years ago, while methane levels increased about 3000 years ago. Many island species began to disappear about 6000 years ago, leading to a great many extinctions. Sloths disappeared in the Caribbean when humans landed during that time. The same thing happened to islands in the Pacific, starting around 30,000 years ago. Islands have suffered the greatest impact of human migration in past years. In the US, Hawaii has suffered the greatest number of extinctions. Australia is essentially a large island that once had many different larger animals. Marsupials, birds, and reptiles were once much larger. Humans have had an impact on the extinction of may of these species; however, there may have been other contributing environmental factors. Human arrived in Madagascar about 2000 years ago, causing the extinction of nearly all indigenous forms of megafauna. Hunting was the major cause of this extinction phenomenon. This originally led to the increase in the numbers of smaller fauna because of lack of competition but these declined around 500 years ago. Every animal species weighing more than 10 kilograms has died out. New Zealand is geographically isolated and has been for the past 80 million years. It has been colonized relatively recently—in about the 12th century. Mass extinction of all large birds shortly died out. Invasive species of rat, cats, and opossums have also destroyed the native birds, most

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of which were flightless. Bird life has suffered the greatest since the islands became inhabited by humans. In the Americas, the loss of glaciation has caused the decrease of many of the megafauna of these areas. Woolly mammoths probably disappeared to some extent prior to human intervention, probably due to climate change. Even so, humans hunted the mastodons and the woolly mammoths. The Clovis people were early Americans that may have had an impact on animal extinction. Africa has experienced the smallest loss of megafauna compared to other areas of the world. It is believed that this is due to the coevolution of these species with humans and the animals collective fear of humans. In Eurasia, climate change has had a great effect on the extinction of animals like the woolly mammoth. Climate change also affected other megafauna species. The presence of megaherbivores, such as the ruminant animals, has contributed to some degree of climate change. Cattle, in particular, eat plants and emit methane gas through flatulence as part of digestion. About 20 percent of methane emissions come from these types of animals today but it is believed that wild forms of related animals had an effect even before humans. Their extinction in the past has led to reductions in methane gas in the atmosphere. Disease may have played a role in the loss of megafauna since humans came to dominate. Domesticated animals, livestock, or humans themselves may have introduced virulent species to environments that had not been exposed to them. This theory is less popular because such a phenomenon would have to affect many species and would have to have a high infection rate plus high mortality rates. Defaunation is the loss of fauna from the environment. It is largely from human activities. This is not the same as extinction because the animals are not truly extinct but have markedly reduced numbers. Animals at risk include gorillas, lions, leopards, cheetahs, and tigers. Cheetahs are especially endangered. Pollinators have also declined, which include insects and birds. Other species at risk include giraffes, other primates, rhinoceros, and anteaters. The most recent extinctions are the most related to human influences. These include certain deer, Hawaiian crows, panthers, insects, butterflies, and birds. Overexploitation, such as overfishing and poaching are human influences on marine life and other larger species of animals. Trophy hunting plays a big role so steps have been made to decrease this factor related to extinction. African elephants have been extensively poached for ivory and trawling has killed off apex predators in the ocean, such as sting rays, sharks, whales, and bluefin tuna.

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Amphibians have been greatly affected by the loss of habitat from humans. They have also been subjected to losses by predators, pollution, and fungal infections. These are more endangered than any other vertebrate group. Bats have had losses because of fungal infections, particularly in the Americas. Beehives have been lost by pesticide ingestion.

WAYS HUMANS MIGHT EVOLVE There have been many theories on how humans will evolve in the future. Some say were will have high foreheads and large brains but this hasn t been borne out in archaeological and fossil records. Others say that humans will not evolve further; however, the human genome has been changing over time. Most of the changes in human evolution so far has been behavioral and physiological rather than morphological. As we have already discussed, there have been many hominid species over time, including the arrival of Homo sapiens in Ethiopia nearly 200,000 years ago. Over time, migrations of humans have led to the different races of humans. Because of the connectivity of the human races, there has been no recent speciation of humans. Even so, genes have changed to a significant degree, even in the last 5000 years, mostly because of adaptations to the environment. Lactose tolerance and intolerance are some of these changes that have occurred. Because of extreme advances in global transportation, the gene pool has become mixed in humans. It might further bring out the homogenization of the human species. Technology has placed a monkey wrench in natural selection so that babies do not die in great numbers and people with once fatal genetic diseases now do not die to the greatest extent that once happened. One interesting shift in human evolution is that college students have fewer children and later starts in parenting than their less-intelligent high school classmates. This may mean that genes for lesser intelligence may increase in the population, driving down the average intelligence in the human race. This has not yet been found to be the case. An argument against this is that intelligence is not necessarily entirely heritable. On the other hand, ADHD and Tourette s syndrome have higher heritability and could increase in society. Alcoholism may also increase due to heritability of this tendency. Humans may in the future become different due to genetic engineering but we are a long way away from having this happen. One other theory is that humans could become symbiotic or synthesized along with machines. Some have forecasted that humans could upload their minds to robots or computers, leading to an intimate connection to them. Advanced artificial

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intelligence could shape the way the world works so that humans could create many copies of themselves in computers.

HUMAN EXTINCTION Human extinction is, of course, hypothetical as it has not happened yet. Even so, extinction could happen because of human actions, natural disasters, or disease. Things like biological warfare, nuclear extinction, pandemic agents, climate change, overpopulation, and climate change are more likely to play a role in human extinction than a natural disaster such as volcanism or a meteorite impact. Some believe that humans have a 95 percent chance of becoming extinct in the next 8 million years. Others argue that, as long as earth is habitable, there will be humans on it and these will thrive. Possible doomsday scenarios include biological and nuclear warfare that would annihilate the human race. Some type of pandemic could destroy the human race, even those that are geographically isolated. Climate change could render the earth uninhabitable. Population decline could happen with humans having fewer children. An extraterrestrial event is less likely but still could happen. The human race was at 1 billion in 1800 but is now over 7 billion. This has led to an increase in human use of land and a possible threat to human habitats in the future. Some predict that human population numbers will peak at 12 billion people. The sun will ultimately grow and effectively destroy the oceans in about a billion years. Before this happens, however, carbon dioxide levels will be so high that plant life will not be possible. The earth will be sterilized by the expanding sun in about 7 billion years. Human technology could also lead to human extinction. Some theories include the creation of a super-intelligent entity that annihilates humans, uncontrolled nanotechnology destroying the ecosystem, or the creation of a small black hole through scientific experimentation. Alien invasion has been considered as a possibility but this has become unlikely. A new species of superhumans could evolve that will edge out regular humans. As long as some people survive, however, the human race is unlikely to completely die out. The extinction of the human race because of humans themselves is called omnicide. Most think it could happen because of biological warfare, nuclear war, or ecological catastrophe. Preventative measures include colonization of other planets or the isolation of some humans on earth itself in order to protect the human race from extinction.

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FUTURE OF THE PLANET WITH GLOBAL WARMING Almost all scientists believe that global warming has a great impact on the earth itself as well as on the human race. It is largely caused by an increase in greenhouse gases because of human activity. While global warming can occur for other reasons, most believe that climate change is happening from the activities of humans. Things that have already occurred are changes in season timing, glacial retreat, rising seawater, and extreme weather events. Climate change can occur because of sunspot activity, changes in the sun s output, or human activities. The temperature has clearly begun to rise as part of human activity in the last 100 years. This is largely due to an increase in greenhouse gases. Temperatures may rise in the 21st century to the same levels as existed 3 million years ago, in the Pliocene era. There are several indicators that change in a world that is warming. Increasing parameters are air surface temperature, humidity, ocean air temperature, sea surface temperature, sea level, land temperature, and ocean heat contact. Decreasing parameters are sea ice levels, snow cover, and glacier size. Biological systems have also changed, including the migration of flora and fauna to areas near the poles. The main greenhouse gases are methane, carbon dioxide, and nitrous oxide, which are increasing in concentration. With global warming, there is an increase in extreme weather events, particularly increases in heavy precipitation events. There will be a reduction in subtropical rainfall with increases in equatorial and subpolar precipitation. Dry regions will be drier and wet regions will be wetter. It isn t yet clear if tropical cyclones and flooding has been on the rise since global warming has started. Warm weather records are twice as likely to be broken as cold ones. In the far future, there will be more very hot days and fewer very cold days. The frequency of cyclones will stay unchanged but their severity will increase. The cryosphere or areas covered by snow and ice has diminished and will continue to diminish. Arctic sea ice may be lost altogether by 2100 CE. Snowpack in North America will decline and the loss of glaciers and snow in Greenland and Antarctica will cause sea level rise. Seasonal activities in winter and water supply from glaciers and snowpack will decrease. Oceans are a sink for carbon dioxide. Increases in carbon dioxide level will acidify the oceans so they cannot absorb any more. Oceans will not be able to absorb any more heat from the atmosphere, which can deplete oxygen from the ocean, affecting ocean life. Sea level rises will threaten coastal areas. The rise in sea level is from global expansion and the melting of glaciers and ice sheets. Thermal expansion takes on the greatest role in sea level rise so far.

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Climate change will impact the food chain and agriculture. Certain cereals will be produced to a lesser degree and food security will decrease so more people will go hungry. Droughts are more frequent in parts of the world and there will be affects on human health, such as an increase in tropical diseases. There will be fewer deaths from exposure to cold. The water cycle is affected by temperature, which can affect human water supplies. There will be less fresh water for livestock and irrigation, as well as for mining and industrial use. Migration and conflict will increase as coastal areas become uninhabitable. There could be an increase in political and military conflict should this occur. Larger increases in global temperature will decrease the world s gross domestic product. There will be large impacts on biological systems. Higher carbon dioxide levels will cause increased drought, fire, species invasion, pest infestation, coral bleaching, and storms. Many endangered species will become extinct and there will be a decline in biodiversity. There could be abrupt changes that cause irreversible changes in the ecosystems and in biological systems. Thermohaline circulation in the Atlantic Ocean could shut down but this has about a 10 percent probability of happening this century. Humans themselves could be impacted by heat waves, weather disasters, infectious diseases, low crop yields, changes in mosquito ecology, and marine productivity changes. Mental health issues could impact humans after these disasters happen. Poorer parts of the world will be more affected. Mosquitos could pass on more tropical diseases to both animals and humans. Extreme weather events could affect humans to a much greater degree. The most common diseases that could increase with global warming include malaria and dengue fever. Malaria currently kills 300,000 children per year who are under five years of age. The rate of malaria is believed to increase by about 10 percent in the next 100 years. Dengue fever is also mosquito-borne, affecting up to 100 million people per year. It is an endemic disease in places like Bangladesh. Temperature increases can cause loss of certain habitats and an increase in deaths from high temperatures. Cold snaps can occur due to disruptions in the polar vortex, which is caused by declines in Arctic sea ice levels. This will affect primarily the Northern Hemisphere countries but is expected to be short-term in nature. Water pollution will increase in warmer temperatures and freshwater sources, such as from glaciers and snowpack will decrease. There will be increases in environmental migrants, particularly from island nations and coastal areas. Interpersonal conflict increases with increased temperatures. Wars and conflicts increase

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when there are environmental factors, such as drought and higher temperatures. Electricity may be cut off in areas where electrical lines contribute to hot and dry areas.

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KEY TAKEAWAYS •

The Holocene extinction is the reduction in biodiversity and increase in extinctions because of human impact on the earth.

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Islands have a greater chance of losing species when mankind inhabits them and introduces invasive species.

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There are many possibilities for human evolution. Most scientists agree that there have been physiological changes in humans since the dawn of mankind.

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Human extinction is probable but the exact timing for this is unclear. It is unlikely to have total annihilation of the human race because of most manmade catastrophes.

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Eventually, CO2 levels will rise, the oceans will evaporate, and the earth will be sterilized by the enlarging sun.

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There are numerous effects on the environment because of global warming, including rising temperatures, decreases in snowpack and glacier sizes, and rising sea levels.

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Humans will be greatly impacted by global warming, which will affect human health, the economy, and food security.

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QUIZ 1. Which term does not describe the mass extinction event that may be occurring in today’s time? a. Anthropogenic extinction b. Holocene extinction c. Paleogene extinction d. Anthropocene extinction Answer: c. Each of these is considered the same term, except for Paleogene extinction, which is linked to the Cretaceous-Paleogene extinction that occurred 66 million years ago. 2. What habitat makes up the majority of the land in today’s time? a. Population centers b. Pastures c. Forests d. Crop fields Answer: b. About a quarter of the earth is consumed by pastures that do not carry wildlife to the same degree as do land areas that contain forests or other natural spaces. 3. Which type of species has been most affected by the habitation of humans on islands like New Zealand? a. Fish b. Birds c. Small mammals d. Apex predators Answer: b. Birds species have suffered the most in places like New Zealand, where humans have taken over and have introduced invasive species.

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4. What factor led to the greatest decline in the woolly mammoth population? a. Human predation b. Mass extinction events c. Climate change d. Disease Answer: c. Climate change and the loss of habitat for the woolly mammoth has likely led to the extinction of these animals, even though humans have had a smaller effect on these populations. 5. Which area of the world is least affected by the reduction in megafauna? a. Arctic and Antarctic areas b. Africa c. New Zealand d. Americas Answer: b. Because African species coevolved with humans, they have been affected the least by human intervention, although this may change due to overhunting of many species of larger animals. 6. Which vertebrate species type is most endangered today because of habitat loss and diseases? a. Fish b. Big cats c. Amphibians d. Birds Answer: c. Amphibians are the most affected species type because of large losses of habitat and by fungal infections that have killed off many of their numbers.

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7. While human extinction is theoretical, what is the least likely cause of human extinction in the future? a. Biological warfare b. Nuclear war c. Natural disasters d. Pandemics Answer: c. Natural disasters, such as volcanism or meteorite impacts, have the least likely possible impact on human extinction. 8. What extraterrestrial event is more likely to destroy the population the soonest? a. Meteor impact b. Ocean evaporation c. Carbon dioxide rise d. Sun growth and earth sterilization Answer: a. Each of these things is on target to happen but not for about a billion years or more. A meteorite impact is much more likely to occur before these other events can happen. 9. What parameter will increase rather than decrease with a rise in global warming? a. Ocean heat levels b. Glacier size c. Snow cover size d. Ocean ice levels Answer: a. Each of these parameters will decrease except for ocean heat levels, which are predicted to increase rather than decrease.

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10. What is not a greenhouse gas? a. Nitrous oxide b. Carbon dioxide c. Ozone d. Methane Answer: c. These represent the major greenhouse gases, except for ozone, which is not a greenhouse gas.

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SUMMARY This course was designed to teach the interested college-level student the fundamentals of evolution. As you have come to understand, evolution is a field of science that is continually changing as more is understood about cell biology, genetics, and the study of the early earth environment. You ve learned that the process of evolution involves the adaptation of organisms to their environment and the ways in which organisms find their niche or surpass other organisms in the process of natural selection. The course talked about the origins of life and helped you understand what we know about how life has evolved on earth throughout the ages. As you hopefully learned from the course, evolution is not just a historic event but is a process that continues in today s time and will continue to be part of life on earth in the future. After studying evolution, you now know that no study of evolution would be complete without a discussion of the history of evolutionary theories, which was the topic of chapter one in the course. We talked about some of the early evolutionists who gave rise to what we currently believe about how evolution works. We then discussed in more detail about evolutionary thought throughout time, including modern evolutionary thinking. The story of Charles Darwin is a good one and hopefully helped you understand how his major breakthroughs in the understanding of evolution as a naturalist in the Nineteenth Century helped to pave the way for modern evolutionary thought. The focus of chapter two was natural selection. It is a key evolution-related process involving the ability of different organisms in a population to adapt to its environment and to pass on this adaptability to their offspring. As you have seen in this chapter, natural selection relates to fitness in a given environment and an organism s reproductive success. Examples of natural selection were given as well a discussion of how natural selection relates to complex behaviors in higher-order animals—a phenomenon known as evolutionary psychology.

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Chapter three in the course talked about the evolutionary relationships between the different types of living things. It started with a discussion of taxonomy, which is the naming convention used to describe all living things. Every form of life falls under one of three domains, Bacteria, Archaea, and Eukarya. There are other subdivisions that describe these types of arrangements. Exactly how to describe the relationships between life forms involves a discussion of phylogenetic trees. As you have seen, newer findings in biology and microbiology have changed the way these phylogenetic trees are arranged. Chapter four was a discussion of genetics and genetic variation. Genetics works on a small scale in the inheritance of certain traits by a descendant from a direct ancestor. It also works on a large scale because it is through a series of genetic mutations that new species are ultimately created. We talked about about Mendelian genetics, the science of mutations, and the advantages and disadvantages that come with certain genetic situations. Chapter five in the course introduced topics related to the origin of life on earth. Life on earth in the beginning of time was very different than it is now. This is partly due to the fact that the early conditions of earth as a planet were vastly different from that of present-day time. The chapter talked about the evolution of viruses and of prokaryotes, which were the first cells to represent life on this planet. There is more to be said about evolution than the evolution of single-celled organisms so this was the topic of chapter six. Eukaryotes are infinitely more complex than prokaryotes—even those that are unicellular. Many eukaryotic organisms are multicellular; for this reason, the evolution of multicellularity was discussed in this chapter. Because evolution happens to populations rather than to individuals, it was important to also talk about the evolution of individuality. There are advantages to evolving in a social environment, which was also covered in this chapter. The major topics of chapter seven in the course were species and speciation. Earlier chapters talked about evolution and its role in the diversity of species on earth. In this chapter, we talked about how species are defined and the different methods in which speciation or the formation of a different species occurs. Historically, species were

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defined by their similar characteristics but, in this chapter, we talked also about how the knowledge of genetics has changed the definition of what exactly is meant when referring to an organism being of a certain species in today s scientific terms. Chapter eight talked about the evolution of the human species. From an evolutionary perspective, humans have not been around very long. Even so, there have been many changes that have taken place over the course of about 400,000 years. As you have learned in the chapter, there have been changes in brain size and gait, among other things, that have been a part of the processes necessary to turn ancient species into modern man. The topic of chapter nine in the course was extinction, which is the final termination of a specific organism type or species. This has occurred to 99 percent of all species that have ever lived on earth. We talked about background extinction, which happens over a period of time for a variety of reasons, as well as extinction events that have occurred in the earth s history, leading to the mass extinction of many of the species on earth at roughly the same time. Chapter ten discussed those issues related to the evolution of reproduction. There are basically two broad categories of reproduction, which are asexual reproduction and sexual reproduction. There are evolutionary advantages and disadvantages of both that were compared in this chapter. With sexual reproduction, in particular, there are complex variables involved in mate selection, which were covered along with the evolutionary issues related to human sexuality and human sexual reproduction. The focuses of chapter eleven in the course are evolution within populations and the evolution of social behaviors. Anytime there is a group of individuals in a population, there will be issues of conflict and cooperation, which were discussed in the chapter. Social behaviors are complex but have genetic and evolutionary influences. Topics also included in the chapter were the Hardy-Weinberg Principle and the evolution involved in finite populations. Chapter twelve focused on the subject of coevolution. Coevolution is a phenomenon that happens when two or more species affect each other s evolutionary processes. This can happen when two species have a mutualistic relationship or when there is a host-

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parasite relationship. There are two other types of coevolution that were discussed in this chapter, including antagonistic coevolution and mosaic coevolution, which involve specialized relationships between two or more species. The focus chapter thirteen in the course was evolution and disease. Diseases affecting all species have been around since the beginning of time. The way in which diseases have originated was discussed in this chapter, including how some human diseases have crossed species to affect humans. Also covered in the chapter was the evolution of senescence or aging. There are several theories as to how and why humans age, which were discussed in the chapter.

Chapter fourteen looked at the future of evolution, particularly of humans and of the planet itself. We talked about what s already happened with the Holocene extinction, often called the sixth mass extinction event on earth. Exactly how humans will evolve is unknown but scientists can make some speculations, which were discussed in the chapter. Human extinction

was covered as a possibility as was the future of the planet with the progress of global warming, which will affect the earth itself and the humans on it.

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COURSE QUESTIONS AND ANSWERS 1. Who first developed a scientific method for the naming of organisms in the environment? a. Carl Linnaeus b. Comte de Buffon c. James Hutton d. Erasmus Darwin Answer: a. Carl Linnaeus was an 18th century botanist, who first described the different species in terms of their genus and species names. He used physical similarities to decide the different relationships between the species. 2. According to Erasmus Darwin, what led to the survival of a species? a. Better adaptation to the environment b. Beneficial mutations with a species c. Better genetic makeup d. Competition among males of a species Answer: d. Erasmus Darwin had some unique ideas about reproduction and embryonic development. He believed that competition among males of a species led to the survival of the fittest among them. 3. Which scientist did not believe in natural selection? a. Empedocles b. James Hutton c. Carl Linnaeus d. William Wells Answer: c. Each of these scientists supported the ideas of natural selection, while Carl Linnaeus was mainly responsible with naming conventions for different species. 205

4. Who did Charles Darwin work with in order to give rise to his theories on natural selection? a. Lamarck b. William Wells c. Robert Chambers d. Alfred Wallace Answer: d. Charles Darwin worked with Alfred Wallace to publish a paper on natural selection in 1958. 5. Which scientist was the first to back up the theory of natural selection through demonstrative research? a. Robert Chambers b. Edward Blythe c. Geoffroy Saint-Hilaire d. Charles Darwin Answer: d. Charles Darwin did extensive research that proved his theories of natural selection by studying species on the Galapagos Islands. 6. What is not one of the more recent developments in evolution? a. Horizontal gene transfer b. Natural selection c. Molecular genetics d. Three-domain theory Answer: b. Each of these is a recent development in evolutionary thought except for natural selection, which has been around for hundreds of years.

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7. Who believed that living things arose from the decomposition of earlier forms of life? a. Origen of Alexandria b. Augustine of Hippo c. Aristotle d. Pliny the Elder Answer: b. Augustine of Hippo was relatively revolutionary. He believed in the gradual transition of life over time and believed that later living things arose from the decomposition of earlier forms of life. 8. In Christian philosophy, what was not true of the great chain of being? a. God is at the top of the chain b. Living things cannot change their position in the chain c. Hell is at the top of the chain d. Amoebae are the lowest form of animal life Answer: d. According to the great chain of life, each of these is a part of the chain except that worms were considered the lowest form of animal life. Living things cannot change their position on the chain. 9. Who first proposed that there was no conflict between theology and natural evolutionary processes? a. Thomas Aquinas b. Johann Herder c. Gottfried Leibniz d. Pierre Maupertuis Answer: a. Thomas Aquinas did not believe there was a conflict between theological beliefs and natural evolutionary processes. He believed that God set the stage with the idea that the natural processes would follow in a non-interventionist way.

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10. Who believed that evolution was based on gradual geological processes rather than on cataclysmic events? a. George Cuvier b. Charles Lyell c. Adam Sedgwick d. William Buckland Answer: b. Each of these theorists believed mainly that cataclysmic events contributed to evolutionary changes except for Charles Lyell, whose work was more based on gradual processes in geology rather than catastrophes in nature. 11. What theory immediately preceded the idea of evolution? a. Transmutation of species b. Essentialism c. Natural theology d. Lamarckism Answer: a. The transmutation of species looked at the different ways that species changed over time, which immediately preceded the main theory of evolution. 12. What did the finding of the Archaeopteryx do to help define evolution? a. Explained the evolution of horses b. Indicated the extinction of dinosaurs c. Showed the origins of bird species from reptiles d. Showed the origin of certain insect species Answer: c. The discovery of the Archaeopteryx species helped to define the ways in which birds evolved from reptiles.

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13. What was not an area of study Darwin himself was involved in? a. Psychology b. Geology c. Fossils d. Zoology Answer: a. Darwin studied many things as part of his research into the origin of species, including geology, the study of fossils, and zoology. He gathered many fossil and zoological specimens. 14. What type of animal did Darwin study the most on the Galapagos Islands? a. Sea turtles b. Fish c. Finches d. Insects Answer: c. Darwin collected numerous finches on the Galapagos Islands and actually found about twelve different species of this type of bird on the island. 15. What is another name for the ability to select a mate among other mates that might be similar? a. Natural selection b. Fecundity selection c. Adaptation d. Sexual selection Answer: d. Sexual selection is the ways in which organisms select a mate based on features of the mate that make him or her more capable of having genetically successful offspring.

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16. What is the selection of certain traits in an organism that make it better at reproducing either more or better offspring successfully? a. Natural selection b. Fecundity selection c. Artificial selection d. Sexual selection Answer: b. Fecundity selection is the selection of certain traits in an organism that make it better at reproduction in general and at making more successful offspring. 17. What is it called when natural selection leads to the formation of an ecological niche for a specific organism? a. Microevolution b. Speciation c. Macroevolution d. Adaptive evolution Answer: a. The actual formation of an ecological niche for a specific organism in a population is referred to as microevolution. 18. The formation of a new species through natural selection is specifically referred to as what? a. Microevolution b. Formation of an ecological niche c. Macroevolution d. Adaptive evolution Answer: c. Macroevolution is a part of speciation, which is the formation of a new species through natural selection.

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19. What is true of an organism’s trait that is selected against? a. It decreases reproductive success b. It increases reproductive success c. It often kills the organism prematurely d. It prolongs the longevity of the organism Answer: a. Traits that are selected against will decrease the organism s reproductive success. Those that are selected for will increase reproductive success. 20. In Manchester, England, the industrial revolution caused lichen to disappear from trees. What did this phenomenon select for in this environment? a. The development of light-colored moths. b. The development of long-legged beetles. c. The development of dark-colored moths. d. An increase in birds that ate moths as part of their diet. Answer: c. When lichen disappeared from trees, the bark was dark and dark-colored moths were selected for and became more predominant. This disappeared when the Clean Air Act reversed the process to allow for the lichenification of trees again. 21. What is not true of competition in an environment? a. It can happen within or between species. b. It is more prevalent where the territory is small. c. It depends on limited resources. d. It is based on the idea that both population expansion and food sources increase arithmetically. Answer: d. Competition is based on the idea that an unchecked population will increase exponentially, while food source increases arithmetically.

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22. Selection can be of different types. What type of selection increases the longevity of an organism? a. Fecundity selection b. Viability selection c. Reproductive selection d. Gametic selection Answer: b. Viability selection involves those forces that increase the longevity of the organism regardless of its ability to reproduce. The other choices are related to reproduction success of the organism. 23. What is not true of mutations when it comes to natural selection? a. It can affect single genes or whole chromosomes. b. Some mutations do not have a major effect and are called neutral. c. Whether a mutation is advantageous or disadvantageous is dependent on the environment. d. Most genetic mutations result in an advantage to the organism. Answer: d. Each of these is true of a genetic mutation except that most mutations are harmful or deadly to the organism. 24. What is not true of genetic hitchhiking? a. It allows for some slightly deleterious genes to be selected for anyway. b. It happens when genes are located on different chromosomes. c. It allows for some genes to be selected against, even if they are benign. d. The process happens because of recombination in the formation of gametes. Answer: b. Each of these is true of genetic hitchhiking except that it occurs when two alleles or genes are located close to one another in the genome of an organism.

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25. What does teleology most refer to? a. The ability to compete with others in the same species. b. The sexual selection of a mate. c. The ability to have genetic drift happen in a population. d. The structure and purpose of an organism’s features. Answer: d. Teleology refers to the structure and purpose of an organism s features. It implies that the form of an organism s features determines their functions. 26. What aspect of a population leads to a species having functional and practical differences? a. Reproductive isolation b. Adverse genetic mutations c. Adaptations d. Sexual selection Answer: c. It is adaptations that lead to functional and practical differences within a species. Speciation also leads to diversity but this involves different species rather than one species that simply has adaptational differences. 27. What most involves an adaptation of an organism? a. Flexibility b. Learning c. Instincts d. Acclimatization Answer: c. Adaptations must be heritable and, among these choices, instincts are the only change in an organism that can be inherited. The others develop throughout life.

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28. Which animal is least generalist when it comes to flexibility to the environment? a. Humans b. Rats c. Carnivores d. Koala bears Answer: d. Koala bears and related herbivores are not very flexible because they only eat a certain type of food. The other choices are more flexible when it comes to adapting to different environments. 29. What is the least likely outcome of a habitat that changes too fast for genetic changes to happen in a population? a. Improved adaptation b. Extinction c. Habitat tracking d. Evolutionary rescue Answer: a. If the habitat changes too fast for genetic changes to happen in a population, there can be habitat tracking, which involves moving away, evolutionary rescue, where the species is rescued from extinction, or there can be extinction of the species. 30. The evolution of palatable species into a structure that makes them appear to be unpalatable is called what? a. Evolutionary rescue b. Mimicry c. Adaptation compromise d. Habitat tracking Answer: b. Mimicry happens in certain species of insects that have evolved to appear to be unpalatable because they mimic insects that are actually unpalatable.

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31. What factor least plays a role in reproductive success of an organism? a. Parental investment b. Reproductive success of the offspring c. Longevity of the organism d. Mate selection Answer: c. Each of these plays a role in determining reproductive success except for the longevity of the organism, which does not always play a role in fecundity. 32. What is not a principle of evolutionary psychology? a. The brain largely operates because of conscious choice. b. The brain has inherited adaptive mechanisms. c. The brain’s adaptations were present from the time of the hunter-gatherer society. d. Complex behaviors have a subconscious component. Answer: a. Each of these is true of the principles of evolutionary psychology except that researchers do not believe that the brain is largely a matter of conscious choice. 33. What is not one of the three main domains of human life? a. Bacteria b. Archaea c. Eukarya d. Viridae Answer: d. Viridae or viruses do not represent a domain of life because viruses are not cellular and therefore are not considered a form of life.

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34. Which subdivision of living things is considered the smallest? a. Genus b. Phylum c. Kingdom d. Family Answer: a. Of these listed the classification of genus is considered the smallest. The smallest known subdivision is just smaller than genus, which is the organism s species. 35. Which subdivision of living things is considered the largest? a. Genus b. Phylum c. Kingdom d. Family Answer: c. Kingdom is just beneath domain and is the second-largest subdivision of living things when it comes to their taxonomic classification. 36. When a group of organisms has an ancestor but does not have all of the descendants included, what is this group called? a. Monophyletic b. Polyphyletic c. Paraphyletic d. Cladistic Answer: c. A group of organisms that has been defined as having a common ancestor but does not have all of its descendants included is called paraphyletic.

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37. In taxonomic systems, there are two separate divisions for plants and animals. What is used in place of phylum in the animal kingdom? a. Division b. Clade c. Family d. Subdivision Answer: a. Instead of phylum in the plant kingdom, the term division” is used instead. The rest of the taxonomic ranks remain the same. 38. What is a phylogenetic tree called that estimates the time period between descendants and when they broke off from the ancestor? a. Rooted tree b. Unrooted tree c. Bifurcated tree d. Molecular clock diagram Answer: d. In a molecular clock diagram, the time period between descendants and when they broke off from a common ancestor is estimated. 39. Similar traits between species that arise independently from one another from a common ancestor are called what? a. Homologous traits b. Analogous traits c. Derived traits d. Ancestral traits Answer: b. Analogous traits are those that arise independently from one another even though they seem similar in appearance.

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40. What are now the most commonly used characteristics to define clades and phylogenetic trees? a. Structural traits b. Protein differences c. DNA differences d. Biochemical differences Answer: c. Differences and similarities in the DNA of different organisms are now commonly used to describe the different clades and to develop the phylogenetic trees. 41. In a clade, what term represents a trait that has been retained by the ancestor to the descendants? a. Plesiomorphy b. Autapomorphy c. Apomorphy d. Symplesiomorphy Answer: a. A structural or biochemical trait that is retained by all of the descendants of a specific ancestor is called a plesiomorphy. 42. What is the basis of the Great Chain of Life interpretation used by early taxonomists? a. There was a common ancestor to all forms of life. b. Living relationships were ordained by God. c. Plants have a different ancestor than animals. d. Bacteria were the first forms of life. Answer: a. In the Great Chain of Life, mankind is at the top but there was a common ancestor to all of the different forms of life.

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43. What is least likely to be used to look into genetic relationships between different organisms in phylogenetics? a. DNA sequencing b. Protein sequencing c. Behaviors d. Morphologic characteristics Answer: c. Each of these can be used to study phylogenetics but behaviors are least likely to define a specific evolutionary characteristic shared among the different descendants in a phylogenetic tree. 44. What is meant by the phrase “ontogeny recapitulates phylogeny”? a. Homologous traits indicate a common ancestry in a group of descendants. b. There is not a common ancestor to all living things. c. Biochemical principles better predict phylogeny than morphological traits. d. The embryonic development of an organism shows its phylogeny Answer: d. The phrase ontogeny recapitulates phylogeny” indicates that the embryonic development of an organism best shows its overall phylogeny. This idea is no longer considered valid in discussing phylogeny. 45. What is not a limitation of using molecular techniques to uncover the phylogeny of organisms? a. It does not account for convergences in the branches of the tree. b. It cannot make use of whole genomes for analysis. c. It does not take horizontal gene transfer into account. d. It assumes a common ancestor or a rooted tree. Answer: b. Each of these is true except that molecular phylogeny can make use of whole genomes. It just isn t done often because of the time and expense involved. 46. The concept that both innate and acquired traits could be inherited from the parents was called what?

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a. Pangenesis b. Blended inheritance c. Lamarckism d. Mendelian inheritance Answer: a. Based on the theory of pangenesis, there could be acquired traits or innate traits inherited from the parents. This was one of Charles Darwin s beliefs. 47. What is the process of turning the DNA code into an RNA messenger called? a. Amplification b. Replication c. Transcription d. Translation Answer: c. The transfer of the DNA code into an RNA messenger is referred to as transcription. It is just one step involved in the making of proteins from a piece of DNA in a gene. 48. What does it mean when a trait or characteristic isn’t 100 percent heritable? a. Acquired traits from the parents partially explain the feature in the offspring. b. There are environmental and inherited factors that play a role in the end result. c. There are too many genes that factor into the inheritance. d. There is blended inheritance going on in the heritability of the trait. Answer: b. When something is not 100 percent heritable, it means that there are inherited and environmental factors that determine the end result in the offspring.

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49. What is the combination of the nucleic acids and organizing proteins in the chromosome called? a. Genome b. Histones c. Gene d. Chromatin Answer: d. The chromatin is what the combination of nucleic acids and organizing proteins in a chromosome is called. 50. The uptake of DNA from another bacterial cell or the environment to another bacterial cell is referred to as what? a. Mitosis b. Horizontal gene transfer c. Sexual reproduction d. Binary fission Answer: b. Horizontal gene transfer can be either conjugation or transformation and involves the uptake of a piece of DNA from outside the bacterial organism. 51. The uptake of DNA from the environment into a bacterial cell is known as what? a. Binary fission b. Asexual reproduction c. Conjugation d. Transformation Answer: d. Transformation is when DNA is taken up from the environment and is incorporated into the genome of the bacterial cell.

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52. What is a true statement about genetic linkage of chromosomes? a. The genes that are close together exhibit a high degree of genetic linkage. b. Chromosomes do not recombine so the entire chromosome is genetically linked. c. Genetic linkage can be demonstrated in egg cells but not in sperm cells. d. Genes that are far from each other on a chromosome will not show any genetic linkage. Answer: a. Genes that are close together on the chromosome will have a high degree of genetic linkage despite the fact that recombination of genetic information happens during meiosis. 53. How many nucleotides together make up a codon? a. 1 b. 3 c. 5 d. 7 Answer: b. There are three nucleotides that make up a codon. There are 64 possible codons that code for 20 amino acids or for instructions to start or stop the translation process. 54. What percent of the offspring of organisms that are heterozygous for a dominant and recessive trait will be homozygous for the recessive trait? a. None of them b. 25 percent c. 50 percent d. 75 percent Answer: b. About 25 percent of the offspring will be homozygous for the recessive trait if both of the parent organisms are heterozygous for the trait.

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55. If there is a dominant trait and a recessive trait and one parent is heterozygous for the trait, while the other is homozygous for the recessive trait, what percent of the offspring will be homozygous for the recessive trait? a. Zero percent b. 25 percent c. 50 percent d. 75 percent Answer: c. Half of the offspring will be homozygous for the recessive trait, while the other have will be heterozygous and will have the dominant trait. 56. What is the genotype going to be for a recessive trait in an organism that shows the recessive phenotype? a. It will always be homozygous for the recessive trait. b. It can be homozygous or heterozygous for the recessive trait. c. It will be heterozygous for the recessive trait. d. It will be heterozygous 95 percent of the time but a few will be homozygous. Answer: a. In the expression of a recessive trait, the organism must be homozygous for the recessive trait all of the time. If not, the phenotype will show the dominant trait. 57. What is the genetic makeup of an organism rather than its physical appearance? a. Phenotype b. Haplotype c. Genotype d. Diploid type Answer: c. The genotype is the genetic makeup of an organism, which ultimately plays a role in its physical appearance, which is called its phenotype.

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58. What is the genotype going to be for a dominant trait in an organism that shows the dominant phenotype? a. It will always be homozygous for the dominant trait. b. It can be homozygous or heterozygous for the dominant trait. c. It will be heterozygous for the dominant trait. d. It will be homozygous 95 percent of the time but a few will be heterozygous. Answer: b. The organism will be homozygous or heterozygous for the dominant trait but you would not be able to tell the difference because the recessive trait will be hidden in the phenotype. 59. What is the cause of differences in the appearance in the populations of a species that happens with geographic distance between them? a. Genetic drift b. Deleterious mutations c. Genetic recombination d. Aneuploidy Answer: a. Because of genetic drift, populations separated by geography may actually appear different despite being of the same species. 60. What is more likely to decrease genetic variability rather than increase genetic variability? a. Natural selection b. Genetic drift c. Climate change d. Genetic recombination Answer: c. Each of these will increase genetic variability, except for climate change, which can decrease genetic variability by decreasing population size.

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61. What is not a cause of DNA mutations? a. Exposure to carcinogens b. Cancer c. Exposure to radiation d. DNA replication errors Answer: b. Each of these can be a cause of DNA mutations except for cancer, which is the result of DNA mutations rather than a cause. 62. About how old is planet earth from the time it was first coalesced from space gas and dust? a. 10 billion years b. 4.5 billion years c. 2.6 billion years d. 100,000 million years Answer: b. The earth itself is about 4.5 billion years old. This is the geological age of the earth and does not represent the age of when life first formed on the planet. 63. In what era did the dinosaurs live on planet earth? a. Cenozoic b. Paleozoic c. Mesozoic d. Archean Answer: c. In the Mesozoic era, dinosaurs came to be the dominant life form on earth and also become extinct, which marked the end of the Mesozoic era.

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64. About how long ago did the first life forms likely begin on planet earth? a. 8 billion b. 7.5 billion c. 5 billion d. 3.5 billion Answer: d. Life on earth most likely occurred around 3.5 billion years ago. This was exclusively made from unicellular, simple life forms. 65. What percent of all life forms that have lived on earth have since gone extinct? a. 1 percent b. 33 percent c. 66 percent d. 99 percent Answer: d. About 99 percent of all the life forms that have lived on planet earth throughout the years have gone extinct. 66. What is not considered a greenhouse gas? a. Methane b. Oxygen c. Carbon dioxide d. Nitrous oxide Answer: b. Each of these is a greenhouse gas contributed by volcanoes in early earth. Oxygen, however, is not a greenhouse gas. 67. What did the earliest common ancestor of all living things look like? a. Fungi b. Algae c. Eukaryotic cells d. Bacteria Answer: d. The earliest common ancestor of all living things was a prokaryote, most likely very similar to the bacteria that exist today.

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68. What is most true of green sulfur bacteria and purple sulfur bacteria? a. They live in normally inhospitable environments. b. The get nutrients from the environment rather than photosynthesis. c. They make oxygen as a byproduct. d. They are recent additions to the tree of life. Answer: a. These bacteria are very ancient and participate in photosynthesis. The end product is not oxygen and they live in inhospitable environments. 69. What characterizes the third atmosphere that has existed on earth? a. Greenhouse gases b. Hydrogen c. Oxygen d. Helium gas Answer: c. The third atmosphere that has existed on earth consists of higher quantities of oxygen. The other gases contribute to the first and second atmospheres on the earth. 70. The earliest common ancestor of all living things is most like what organisms living today? a. Sulfur-producing photosynthetic bacteria b. Anaerobes living near thermal vents c. Oxygen-producing photosynthetic bacteria d. Filamentous prokaryotic organisms Answer: b. The earliest common ancestor of all living things was probably similar to anaerobes that live near thermal vents in the oceans today.

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71. What is true of the earliest life forms on earth? a. They thrived on oxygen b. There was probably just one form of life that arose on early earth c. Early life was based on RNA instead of DNA d. It is easy to recreate these organisms de novo in the laboratory setting Answer: c. Early life probably did not use oxygen but were based on RNA instead of DNA. There may or may not have been a single life form on early earth but these have not been created in a laboratory setting. 72. What is not true of viruses? a. They need a host in order to replicate. b. They mutate to a higher degree than other organisms. c. They can easily adapt to their environment. d. Almost all viruses have DNA as their nucleic acid. Answer: d. Each of these is true of viruses except that their nucleic acid can easily be RNA or DNA. 73. What is the theory of virus evolution that says viruses were once pieces of DNA in cells that somehow left the cell to form an independent organism? a. Escape theory b. Virus first theory c. Degeneracy theory d. Coevolution theory Answer: a. The escape theory is one in which the virus particle was once part of cellular DNA but escaped the cell to become and independent organism.

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74. Which type of viral transmission involves the least virulent viruses? a. Waterborne transmission b. Vertical transmission c. Droplet transmission d. Airborne transmission Answer: b. Each of these involve horizontal transmission except for vertical transmission. In general, horizontal transmission is more virulent than vertical transmission. 75. What structure is found in both prokaryotes and eukaryotes? a. DNA b. Mitochondria c. Lysosomes d. Golgi apparatus Answer: a. Both eukaryotes and prokaryotes have DNA, ribosomes, cytoplasm, and plasma membranes. Only eukaryotes have mitochondria, lysosomes, and Golgi apparatuses. 76. What type of molecule can self-replicate, making it most necessary for the formation of life? a. Proteins b. Carbohydrates c. Nucleic acids d. Lipids Answer: c. While all cells need each of these things, only nucleic acids are capable of self-replication so they are definitely necessary for life.

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77. Which metabolic pathway to gain ATP energy is the most advanced? a. Fermentation b. Photosynthesis c. Glycolysis d. Oxidative phosphorylation Answer: d. Oxidative phosphorylation is the most advanced pathway that makes the most ATP energy per unit of initial substrate in the food of the organism. 78. What is not considered evidence that mitochondria were once separate prokaryotes? a. The mitochondrial membrane is double-walled. b. The cells can be seen taking up mitochondria from the outside. c. Mitochondria divide by binary fission. d. Mitochondria have their own DNA. Answer: b. Each of these is true of mitochondria except that cells have not been observed taking mitochondria up from the outside. This happened billions of years ago and does not happen today. 79. What is the structure of mitochondrial DNA like? a. Single linear piece of DNA b. Multiple linear pieces of DNA c. Multiple circular pieces of DNA d. Single circular piece of DNA Answer: d. There is a single circular piece of DNA in mitochondria, which is identical to that of the type of DNA seen in bacteria.

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80.What is true of the evolution of chloroplasts and mitochondria? a. The mitochondria and chloroplasts do not have to be present in eukaryotic cells at all. b. All eukaryotic cells have chloroplasts and mitochondria. c. Mitochondria likely evolved to be endosymbiotic first, followed by chloroplasts. d. Chloroplasts likely evolved to be endosymbiotic first, followed by mitochondria. Answer: c. Mitochondria likely evolved to be endosymbiotic first, followed by chloroplasts. The evidence for this is that all eukaryotic cells have mitochondria but only plant cells have chloroplasts. 81. What is not something required in order to have an organism be multicellular? a. The ability to make gametes. b. The ability to specialize or differentiate its cells. c. The ability to have a circulatory system. d. The ability to have cell to cell adherence. Answer: c. Each of these things is necessary for multicellularity except for the ability to have a circulatory system, which is not seen in all multicellular organisms. 82. Which type of organism is least likely to have reverted to unicellularity or loss of some degree of their multicellularity? a. Animals b. Protozoa c. Algae d. Fungi Answer: a. Each of these types of organisms has experienced loss of their degree of multicellularity or has reverted to unicellularity except

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for animal species. Protozoa, Algae, and fungi have all done this as part of their evolutionary process. 83. What phenomenon is unique to multicellular organisms? a. Viral infections b. Cancer c. Bacterial infections d. Mutation Answer: b. Multicellular organisms, because of their differentiation, can develop cancer because it involves losing differentiation of a more advanced cell. 84. What theory of multicellularity involves organisms of the same species coming together to function as one organism? a. Cellularization theory b. Symbiosis theory c. Colonialization theory d. Syncytial theory Answer: c. In the colonialization theory, it is believed that a single species of organism comes together under distress in order to function as a single organism. This is what happens with protists like amoeba. 85. What is not part of the transition process necessary for separate cells to become an individual unit? a. Cohesiveness of the cells b. Competition between the cells c. Division of labor between the cells d. Aggregation of the cells Answer: b. Competition or conflict between the cells cannot occur between the cells if they are to evolve into an individual organism.

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86. What is not an evolutionary benefit of cooperation between cells in an aggregate? a. Direct transfer of nutrients from cell to cell b. Greater dispersal of seeds or young by making fruiting bodies c. Efficiency of factor recognition between cells d. Avoidance of predators Answer: a. Each of these is an evolutionary benefit in cells learning to cooperate in an aggregate except for the direct transfer of nutrients from cell to cell. In fact, cells in an aggregate must find unique ways to transfer and exchange nutrients so that the inside cells get as much nutrients as the outside cells. 87. What is the major cause of mutual dependence between cells of an organism or between organisms in a group? a. Predators can kill them if they aren’t mutually dependent. b. Extreme specialization has occurred in the group. c. Cell to cell communication has curbed independence. d. Growth factors are not present in individual cells. Answer: b. The major cause of mutual dependence is that extreme specialization has occurred so that one part of the whole cannot survive and reproduce without the other part. 88. Which species of animal is least social with members of its own species? a. Ants b. Termites c. Bees d. Wolves Answer: d. While wolves live in packs they are not as social as bees, termites, and ants, which are highly dependent on the ability to live in a colony and cannot easily survive on their own.

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89. Which organisms form social groups for other reasons than to escape predators? a. Bees b. Wildebeests c. Fish d. Birds Answer: a. Each of these types of animals form social groups in order to escape predators, except for bees, which do not form social groups for this purpose. 90. What is not a feature of animal groups that live in colonies? a. There is an advantage to raising children that aren’t related to all members. b. The organisms share tasks among themselves. c. They produce large numbers of offspring. d. Every member has the same reproductive chances. Answer: d. In animals that live in colonies, only a few members of the colony have the ability to reproduce but there is an advantage to workers raising children that are not genetically related to them. 91. A species concept that defines a species by its ability to reproduce sexually with others in the same group is called what? a. Genospecies b. Morphospecies c. Agamospecies d. Biospecies Answer: d. Using the species concept of biospecies defines those that can reproduce sexually with others in the same group.

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92. A species concept that involves defining a species in terms of their ecological niche is called what? a. Ecospecies b. Taxonomic species c. Morphospecies d. Biospecies Answer: a. An ecospecies is a species concept that defines organisms in terms of their ecological niche in the environment. 93. What species type is also referred to as an organism’s typological species? a. Biospecies b. Morphospecies c. Genospecies d. Taxonomic species Answer: b. In the study of evolution and taxonomy, the organism s morphospecies is the same as their typological species. 94. What poses the biggest challenge to identifying different species types, particularly among prokaryotes? a. Horizontal gene transfer b. Lack of fossil record c. Hybridization d. The presence of quasispecies Answer: a. Horizontal gene transfer is common in bacteria and other prokaryotes, which leads to the possibility of the same pieces of DNA being in prokaryotic species that are actually very divergent species.

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95. Species that are different in a variety of geographical locations that can interbreed if their ecological niches overlap but not if they don’t overlap are called what? a. Microspecies b. Ringed species c. Species aggregates d. Quasispecies Answer: b. Ringed species are related but have different characteristics in differing geographical areas. Where their habitats overlap, interbreeding can occur but this is not a universal phenomenon if the species have geographical differences in habitat. 96. What is the mechanism by which there are changes in a species along the same line of lineage called? a. Natural selection b. Sexual selection c. Anagenesis d. Cladogenesis Answer: c. Anagenesis is the changing of a species along the same lineage lines over time. 97. In sexual selection and mating, what is koinophilia? a. The choosing of brightly colored mates b. The choosing of mates that do not have unusual characteristics c. The fact that males and females of a species appear different d. The choosing of mates with the best reproductive potential Answer: b. Koinophilia involves the selection of a mate that does not have rare or unusual characteristics so that the species similarities remain relatively stable over time. 98. Which mode of speciation involves the same geography but differences in ecological preferences between different types of species?

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a. Allopatric b. Peripatric c. Parapatric d. Sympatric Answer: d. In sympatric speciation, new species develop in the same geographical area but do so because of differences in their preferred niches within that area. 99. Which mode of speciation is also called island speciation because it involves a habitat disruption or difference in the geographic locations of the organisms? a. Allopatric b. Peripatric c. Parapatric d. Sympatric Answer: a. With island speciation or allopatric speciation, there will be the development of new species with new ecological pressures by virtue of having different geographical locations. 100.

What factor plays a role in all modes of speciation?

a. Horizontal gene transfer b. Mate selection c. Geography d. Ecological niches Answer: d. Because ecological niches have the ability to exert different pressures on the organisms, these play a role in all modes of speciation.

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101.

What is not a way of isolating different species and causing speciation in

the laboratory? a. Through differences in habitat preference b. Through forcing genetic mutations with carcinogens c. Through differences in food preferences d. Through exerting different ecological pressures Answer: b. Each of these is a way of causing speciation in the laboratory, except by causing mutations with carcinogens, which tends to produce deleterious mutations and nonviable organisms. 102.

What happens in speciation using polyploidy?

a. There is a meiosis failure that leads to more chromosomes in the offspring. b. A cell divides but does not have division of its cell membrane so there are two nuclei per cell c. A chromosome gets deleted from the offspring. d. The offspring develop an increased ability to procreate so these are favored in evolution. Answer: a. In speciation using polyploidy, there is a failure of meiosis so that the offspring have more chromosomes than the parent. The offspring must be able to reproduce themselves if this is to be successful. 103.

What is the major disadvantage of using DNA technology and genetics to

define a new or different species? a. Too many species get labeled as subspecies rather than unique species b. Species cannot be easily identified as being endangered c. It is too difficult to define what a species is d. It is a more expensive way of defining a species Answer: d. While genetics does define more species than is true of morphologic species identification, this is not a disadvantage and more

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species can be defined as being endangered. The biggest disadvantage is that it is more expensive to define species in this way. 104.

What is a cryptic species?

a. It is a species that has become extinct over time. b. It is any species that has more recently been discovered. c. It is a species that looks like others but is unique genetically. d. It is a species that has become geographically isolated from other species. Answer: c. A cryptic species is hidden because it looks like other species except that it has been discovered to be a unique species through DNA analysis. 105.

Where did modern man first appear on earth, according to archaeological

records? a. Ethiopia b. China c. South Korea d. Peru Answer: a. Most records list modern man as first appearing in archaeological digs in Ethiopia about 160,000 years ago. 106.

Hominine is a subfamily of the family that includes each of these species

living today except for which of the hominids? a. Gorillas b. Humans c. Chimpanzees d. Orangutan Answer: d. The Hominine subfamily includes each of these types of hominids except for orangutans, which are not included as part of this subfamily.

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107.

What term defines each of the great apes, including mankind?

a. Hominine b. Hominin c. Hominid d. Hominoid Answer: c. The great apes are the hominids, which includes gorillas, orangutans, chimpanzees and humans. 108.

Which of these is a species that humans are closest to in evolutionary

time? a. Gorillas b. Chimpanzees c. Gibbons d. Orangutans Answer: b. The separation of humans in the evolutionary process last occurred with the ancestor that led to chimpanzees and humans, making chimpanzees our closest relative. 109.

What is least likely to be an advantage of bipedalism to our early

ancestors? a. Greater use of hands for carrying food b. Better long-distance running ability c. Prevents hypothermia d. Less energy expended in locomotion Answer: c. Each of these is an advantage of bipedalism except that it doesn t prevent hypothermia; instead, it prevents hyperthermia by exposing less of the back to the full effects of the sun.

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110.

Which bony structure needed to change the most as part of bipedalism?

a. Big toe b. Pelvis c. Vertebral column d. Arms Answer: b. The pelvis changed the most as part of the adjustment to bipedalism. The birth canal narrowed and the birthing process became more difficult. 111.

What aspect of the female reproductive system developed as a result of

bipedalism? a. The ability to have longer gestation times. b. Decreased spacing of children during the mother’s lifespan. c. Decrease in the age of menarche. d. The development of menopause. Answer: d. Many reproductive changes happened as a result of bipedalism. There were shorter gestation times, increased spacing of children, later menarche, and the development of menopause so it would be more advantageous to help raise one s grandchildren than it was to have more children at a later age. 112.

Which human species has the largest brain size?

a. Homo neanderthalensis b. Homo habilis c. Homo sapiens d. Ardipithecus Answer: a. Homo neanderthalensis or Neanderthal man had the largest brain size. The smaller brain size of Homo sapiens has been offset by greater strides in growth that occur in the modern human brain after birth has occurred.

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113.

Which part of the brain was least effected by the evolution of humans over

time? a. Temporal lobe b. Prefrontal cortex c. Brainstem d. Cerebellum Answer: c. Each of these has changed considerably as humankind has also changed over time. The brainstem has least changed as this is a very primitive part of the brain, responsible for things like breathing and heartbeat. 114.

What genus was Lucy from, who was found in Ethiopia in 1974?

a. Australopithecus b. Homo neanderthalensis c. Homo erectus d. Denisovan Answer: a. Lucy belonged to the Australopithecus genus, which dated back about 3.2 million years ago. She was found in Ethiopia, which is roughly where mankind originated from. 115.

Which type of early human do most all humans share DNA with?

a. Australopithecus b. Denisovan c. Homo erectus d. Neanderthals Answer: d. Because of interbreeding, almost all modern humans have up to 4 percent Neanderthal genes as part of their genome. A few people in Oceania and Tibet have Denisovan genes.

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116.

Which species of the Homo genus is considered to be the oldest?

a. Homo erectus b. Homo habilis c. Homo ergaster d. Homo neanderthalensis Answer: b. Homo habilis is the original stone-age human and is the oldest ancestor of the Homo genus. The others all came out of this species. 117.

Among these non-Homo primates, which is the closest relative to humans

over evolutionary time? a. Australopithecus b. Orrorin c. Ardipithecus d. Sahelanthropus Answer: a. All of these are precursors to humans but Australopithecus dates back to just 3 to 4 million years ago, which is the most recent form of non-Homo species related to humans. 118.

When did encephalization or the increase in brain size occur in human

evolution? a. Prior to Australopithecus b. Prior to Homo habilis c. After Homo habilis d. After Homo erectus Answer: c. Homo habilis had a very small brain. It was after this and prior to Homo erectus that encephalization occurred and brain size increased.

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119.

What aspect of anatomically modern humans was considered superior to

Neanderthal man, leading to the ascent of man over the Neanderthals? a. Better use of social skills and tools in modern man b. Better visual acuity in modern man c. Greater physical size in modern man d. Bipedal nature of modern man versus Neanderthals. Answer: a. Both Neanderthals and anatomically modern man were bipedal. Neanderthals were larger, stronger, and had better vision than man but men had better social skills, better use of tools, and more mating choices than Neanderthals. 120.

What species did Homo sapiens likely evolve directly from?

a. Denisovans b. Homo floresiensis c. Heidelberg man d. Neanderthals Answer: c. Current evidence suggests that modern man s immediate predecessor was Heidelberg man or Homo heidelbergensis. 121.

What would least likely be a reason why a species would be functionally

extinct? a. Mass extinction event b. Sparsely populated organisms c. Poor health of individuals in the species d. Poor distribution of mating partners Answer: a. Each of these is a common reason why a species would be functionally extinct; that is, having just a few of its numbers left. Mass extinction events in evolution are very rare.

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122.

What happens when a species undergoes extirpation?

a. They evolve to meet the demands of the habitat b. They split into more than one extant species c. They repopulate an area where they were once threatened d. They disappear from their usual habitat Answer: d. Extirpation refers to the disappearance of a species from their usual habitat without a true extinction. This is sometimes referred to as local extinction. 123.

What is an extant species?

a. One that has been repopulated after threatened extinction. b. One that cannot keep up with its death rate by increasing its reproductive rate. c. A species that currently lives on earth. d. A species that mimics a previously extinct group of organisms. Answer: c. Any species that currently lives on earth is referred to as an extant species. 124.

What is the least likely cause of human-related extinction?

a. Mass extinction events b. Destruction of habitat c. Overharvesting d. Pollution Answer: a. Each of these is a cause of human-related extinctions except that humans are not generally involved in mass extinction events over evolutionary history.

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125.

What factors in a species population will least likely lead to the

population’s extinction? a. The small size of a population b. A narrow habitat for the population c. A large degree of genetic diversity d. Population bottlenecks Answer: c. A population with a large degree of genetic diversity will have a decreased chance of extinction rather than an increased chance of extinction. The other choices will increase the chances of extinction. 126.

What is not a cause of genetic pollution?

a. Selective breeding b. Decreased fitness of a hybrid organism c. Bringing two populations together d. Domestication of animals Answer: b. In general, each of these things causes genetic pollution but increased fitness of the hybrid organism is more likely to cause genetic pollution rather than decreased fitness of the hybrids. 127.

What is the main cause of the Holocene extinction?

a. Human population growth b. Climate change c. Natural disasters d. Species competition Answer: a. Human population growth and the overconsumption of the earth s resources are the main cause of what is termed the Holocene extinction.

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128.

What is the major reason for planned extinctions?

a. To decrease the pest population b. To eliminate competitors of desirable species c. To decrease the frequency of a mutant gene d. To get rid of diseases Answer: d. The planned extinctions that have taken place and that are taking place today involve the getting rid of disease-causing microorganisms and to eradicate a specific disease, such as smallpox and polio. 129.

What is not a way to determine the background extinction rate?

a. The estimated survival time for a given species b. The percent of a species that dies off every year c. The number of species million years d. The number of species that go extinct over a time period Answer: b. Each of these can be used to determine the background extinction rate but it is not the percent of a species that dies off every year. 130.

What was the cause of the Cretaceous-Paleogene extinction event that

killed off the land-based dinosaurs 66 million years ago? a. Meteor strike b. Climate change c. Volcanic eruption d. Sea level disruption Answer: a. This extinction event was likely triggered by a meteor strike that markedly affected the climate in the world.

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131.

What is true of evolution and mass extinction events?

a. Evolution temporarily stops when a mass extinction event happens b. Extinction events cause vacancies in certain habitats c. Extinction events allow for a superior species to take hold d. Extinction events affect the evolution of microbes more than multicellular organisms Answer: b. Extinction events cause vacancies in certain habitats but they do not necessarily allow for a superior species to ascend over an inferior species. 132.

What is true of the causes of mass extinction?

a. They are usually caused by competition between species b. They are caused by short-term shocks to the environment c. They are caused by long-term pressures on the ecosystem d. They are caused by a combination of long-term pressures and short-term shocks to the environment Answer: d. Mass extinction is most likely caused by a combination of long-term ecological pressures and short-term shocks to the environment. Either one alone probably doesn t cause a mass extinction. 133.

Which types of species are most at risk during extinction events triggered

by global warming? a. Marine species b. Polar species c. Tropical species d. Temperate species Answer: b. Polar species are most impacted by global warming events because it destroys their habitats and leads to competition from species that have moved to the polar regions.

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134.

Which theory of mass extinctions has largely been debunked as

implausible? a. Anoxic events b. Ocean turnover c. Global warming d. Disease infestation Answer: d. Each of these is a valid theory except for disease infestation, which most likely would not affect the majority of all species at the same time. 135.

The basic process that describes any cell that divides into more than one

daughter cell in asexual reproduction is called what? a. Gametogony b. Merogony c. Schizogony d. Sporogony Answer: c. The process that describes the ability to make several daughter cells from the same parent cell is called schizogony. The parent cell will make multiple nuclei before dividing its cytoplasm to make the daughter cells. 136.

The process by which an organism makes daughter cells inside itself that

digest the mother cell is called what? a. External budding b. Internal budding c. Spore formation d. Vegetative propagation Answer: b. Internal budding involves the presence of at least two daughter cells created inside a parent cell, after which the daughter cells digest the mother cell prior to actually separating.

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137.

What is it called when plants produce tubers, clones, or rhizomes as part of

asexual reproduction? a. External budding b. Internal budding c. Spore formation d. Vegetative propagation Answer: d. Vegetative propagation only happens with plants that reproduce asexually by giving off clones, tubers, or rhizomes that share the genetic material of the mother cell. 138.

What is not true of parthenogenesis?

a. All of the genes inherited by the offspring are of female origin. b. It can be an obligatory thing or something an organism does under certain circumstances. c. It is primarily done in primitive forms of life. d. It yields only female offspring. Answer: c. Parthenogenesis does not just happen in primitive forms of life. It happens with certain species of sharks, snakes, and birds as well, usually under certain circumstances. 139.

What is not a major benefit of sexual reproduction?

a. It can create fitter offspring than the parents. b. It can weed out deleterious genes in the population. c. It can increase the possibility of two beneficial mutations occurring in the same offspring. d. It has the greater chance of increasing the population compared to asexual reproduction. Answer: d. Each of these is a benefit of sexual reproduction except that it does not increase population numbers faster than asexual reproduction but, in fact, is much slower.

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140.

What factor in sexual reproduction is not considered a benefit to the

offspring’s genome? a. The pairing of homologous chromosomes when one contains a deleterious recessive trait. b. The pairing of homologous chromosomes when one contains a deleterious dominant trait. c. The fact of genetic recombination to increase diversity. d. The fact of DNA repair processes during meiosis. Answer: b. Each of these factors will benefit the offspring s genome during sexual reproduction except for the pairing of homologous chromosomes with dominant traits, which do get passed to the offspring and adversely affect the chromosome. 141.

In sexual reproduction, what is the difference between inbreeding and

outbreeding? a. Inbreeding better maintains enhanced vigor in the population. b. Inbreeding is more effective in masking deleterious genes in the population. c. Inbreeding better allows dominant genes to take hold in the population. d. Inbreeding is less effective in masking deleterious genes in the population. Answer: d. Outbreeding is more effective than inbreeding in masking deleterious genes in the population. With inbreeding, the deleterious genes are not as masked by normal genes in the parents. 142.

What is not true of the origin of sexual reproduction?

a. It started in prokaryotes and persisted in eukaryotic organisms. b. It is believed to have started about 1.2 billion years ago. c. It started with a common eukaryotic ancestor. d. It may have persisted because meiosis is evolutionarily beneficial. Answer: a. Each of these is a true statement of sexual reproduction, except that it did not start in prokaryotic organisms.

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143.

What is considered an advantage of asexual reproduction?

a. It increases genetic diversity b. It allows for more rapid evolution c. It can happen in harsh environments d. It masks deleterious mutations Answer: b. The major advantage to the evolutionary process with asexual reproduction is that it happens faster with asexual reproduction, which may be advantageous in populations large enough to tolerate many mutations. 144.

What type of mating system is involved in chimpanzees, who will mate

with any other member of a given group? a. Monogamy b. Polygyny c. Promiscuity d. Polyandry Answer: c. Chimpanzees will mate with any other member, which means they have a promiscuous mating system.

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145.

What mating system is the most common among human systems on

earth? a. Monogamy b. Polygyny c. Promiscuity d. Polyandry Answer: b. Most mating systems in the world among humans are polygynous. About 83 percent of mating systems are considered polygynous. 146.

What is not true of microbial mating?

a. Viruses do not exchange genetic material. b. Bacteria can engage in mating through the conjugation process. c. Archaea can aggregate and can exchange genetic material. d. Protists are eukaryotes that will under stress engage in mating behavior. Answer: a. Each of these is true of microbial mating, except that viruses do exchange genetic material, which is a form of primitive mating. 147.

Under what circumstance would sex role reversal occur in a species?

a. When the female fitness is more important than male fitness to survival. b. When there are more males than females in a population. c. When males participate in rearing their young. d. Sex role reversal does not exist in animals. Answer: c. Sex role reversal happens when males participate in rearing their young.

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148.

What is true of human mate selection?

a. Males look more for long term potential in a female mate. b. Females prefer taller men with deeper voices. c. Males look for a larger waist to hip ratio. d. Males prefer sexually inexperienced females. Answer: b. Each of these is an untrue statement except that women do tend to prefer taller men who have beards and deeper voices. 149.

What is a populations equivalent of an organism’s genome in evolution?

a. Gene pool b. Genetic drift c. Allele frequency d. Genetic fitness Answer: a. The gene pool is the totality of the alleles in a given population, which is the equivalent of the genome in a given organism; it is applied, however, specifically to the population rather than the individual organism. 150.

What plays the least role in the changes in gene pool within a population

of organisms? a. Natural selection b. Founder effect c. Asexual reproduction d. Random genetic drift Answer: c. Each of these plays a role in the changes in the gene pool within a population of organisms except for asexual reproduction, which tends not to change the gene pool because all the daughter cells are clones of the parent.

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151.

The term that describes a population that has organisms that look

different from one another is called what? a. Polymorphism b. Shallow gene pool c. Genetic drift d. Allele frequency Answer: a. Polymorphism describes a population in which the organisms do not look the same as one another. This is also referred to as a polymorphic population. 152.

What is least likely to play a role in genetic variance within a population?

a. Trait heritability b. Inbreeding c. Outbreeding d. Acquired traits Answer: d. Acquired traits are not heritable so that these do not contribute to genetic variance. Each of the other factors will add or subtract from the genetic variance within a given population. 153.

What is the main cause of gene flow in a group of organisms?

a. Inbreeding b. Mutations c. Migration d. Habitat destruction Answer: c. The main cause of gene flow in a group of organisms is migration either into or out of a population, which can change gene and allele frequency.

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154.

What does a cline do to lead to differences in phenotype in a population?

a. It can affect mating habits within a species. b. It is a major contributor to gene flow. c. It is a major contributor to population social behaviors. d. It sets up a gradient in environmental conditions that affects phenotypes. Answer: d. A cline can be altitudinal or latitudinal, for example. It sets up a gradient of different environmental factors that affect the phenotypes of individuals in a population. 155.

What type of selection in a population favors a phenotype that is an

average of two separate phenotypes? a. Diversifying selection b. Stabilizing selection c. Extreme selection d. Diversifying selection Answer: b. With stabilizing selection, the phenotype most often selected for is an average of two separate and extreme phenotypes. 156.

What is the handicap principle of sexual selection in a population?

a. Positive reproductive success can be related to increased risk for the male of a species. b. Females tend to avoid males who have handicaps in some ways. c. Certain sexual traits will handicap the male in his ability to find a good mate. d. Certain genetic traits cause a decrease in the male’s ability to provide for the young. Answer: a. Certain positive traits when it comes to reproductive sex can cause an increased risk for the male of the species, which is called the handicap species. It is the principle in play in male peacock feathers that further reproductive success but increase the risk of predation.

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157.

What best defines a population in Hardy-Weinberg equilibrium?

a. Evolution is a slow process in the population. b. The population does not have mate selection. c. All of the alleles in the gene pool stay at the same frequency. d. There is just a single phenotype present in the population. Answer: c. In true Hardy-Weinberg equilibrium, the alleles in the entire gene pool stay at the same frequency over time. 158.

What is an outcome of a behavior that affects the health of one’s own

offspring? a. Direct fitness b. Indirect fitness c. Inclusive fitness d. Kin selection Answer: a. Direct fitness is the behavior that affects the health of one s own offspring directly. This is an example of cooperation. 159.

Which is an outcome of a behavior that affects the fitness of all the

offspring in a population? a. Direct fitness b. Indirect fitness c. Inclusive fitness d. Kin selection Answer: c. Inclusive fitness is the outcome of a behavior that affects the fitness of all of the offspring in a certain population. It is an example of cooperation.

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160.

What is a cooperative behavior in a population?

a. A behavior that benefits someone but has an adverse effect on the actor of the behavior. b. A behavior that benefits someone and is evolutionarily positive for the group. c. A behavior in which two species are dependent on each other. d. A behavior beneficial to the giver but harmful to the host. Answer: b. A cooperative behavior is any behavior that benefits someone and is evolutionarily positive for the group or population. 161.

Cooperative behavior that is weighted toward increased fitness of one’s

relative organisms is called what? a. Direct fitness b. Inclusive fitness c. Kin selection d. Mutually beneficial Answer: c. Kin selection refers to behaviors that most greatly favor those who are closely related to the actor doing the behavior. 162.

What is not true of kin discrimination in a population?

a. It helps to create kin selection in a group. b. It is generally a positive thing in a group. c. It can involve certain learned vocalizations in a kin group. d. It is practiced by many different species. Answer: b. Kin discrimination can be a bad thing for a population because it has a tendency to decrease genetic variability in the population.

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163.

What is not true of enforcing cooperation among population members?

a. It can be done by punishing cheaters b. It can be done by rewarding cooperators c. It will increase cooperation levels d. It is a necessary part of cooperation Answer: d. Each of these is true of enforced cooperation except that it doesn t necessarily have to occur. 164.

What is not an advantage of group living?

a. Decreased competition b. Increased ability to forage c. Increase in social information d. Better proximity to mates Answer: a. Each of these is an advantage to group living except for decreased competition among group members. 165.

What is not true of evolution in finite populations?

a. There is an increase in heterozygosity in finite populations b. Genetic drift is greater than is seen in infinite populations. c. Neutral mutations will drive the population’s evolution forward. d. Decreased fitness can happen if mutation rates exceed the ability to adapt to the environment. Answer: a. Each of these is true of evolution in finite populations except that heterozygosity will decrease in these types of populations. 166.

What is not true of population bottlenecks?

a. They are usually caused by some type of natural disaster or habitat destruction. b. They will increase the rate of inbreeding. c. They will increase the rate of genetic drift. d. They are not affected by the founder effect.

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Answer: d. These are all true statements of population bottlenecks except that they can result in the founder effect if the population shrinks to a greater degree. 167.

What is not true of flowers that require insects to pollinate them?

a. They tend to be red or orange in color. b. They have certain stripes that guide the insects. c. A flower’s scent can direct the insects to the plant. d. Some flowers have parts that mimic female insect parts. Answer: a. Each of these is true of flowers that require insects to pollinate them, except that they are blue or ultraviolet in color. 168.

What is not true of flowers that use birds to pollinate them?

a. They tend to be red in coloration. b. They have a tubular shape to discourage insects and encourage pollination. c. They have very little nectar in each flower. d. Their relationship is primarily with hummingbirds. Answer: c. Each of these is true of ornithophilous flowers, except that they have a lot of nectar and sugar per flower. 169.

Which type of organism is so much of an obligate parasite that it cannot

survive without coevolution with its hosts? a. Bacteria b. Archaea c. Protists d. Viruses Answer: d. Viruses are entirely unable to develop outside the host so they become obligate parasites that must coevolve with their respective hosts.

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170.

What happens in the situation of brood parasitism?

a. The youth of a litter are particularly targeted by the parasite. b. A viral infection infects the eggs of a specific bird species. c. The parasitic bird deposits camouflaged eggs into another bird’s nest. d. A parasite preferentially infects the gestating female hosts. Answer: c. Brood parasitism happens between two bird species. The parasitic bird deposits camouflaged eggs into another bird s nest so they can be raised by the host bird. 171.

What is an example of a symmetrical evolutionary arms race?

a. Parasites that get more effective at invading a host that gets a tougher skin b. Gazelles that get faster and cheetah’s that get to be stronger hunters c. Bees that grow longer proboscises and flowers that become more accessible to them d. Trees that grow taller in order to compete for available sunlight Answer: d. When trees evolve to be taller in order to compete with other trees that are also growing taller for the same reason, this is an example of a symmetrical evolutionary arms race. 172.

What does the Red Queen Hypothesis refer to?

a. Increased ability to compete for resources in a population b. Constant adaptation occurring over time with antagonistic species c. Decreased host resistance when mutations accumulate d. When virulent species become overly adapted to their host Answer: b. The Red Queen Hypothesis relates to the constant adaptation throughout evolutionary time between antagonistic species, such as a parasite and host.

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173.

What is the main underlying mechanism behind the Red Queen

hypothesis? a. Competition between two species for scarcity of resources b. Changing or adapting to a new habitat c. Mutual selective pressures on two antagonistic organisms d. Decrease in competition when a new organism is introduced into the environment Answer: c. In the Red Queen Hypothesis, there are mutual selective pressures on two antagonistic organisms, which is generally what happens in a predator-prey relationship. 174.

Which relationship between species involves the probable decrease in

fitness of both species involved? a. Exploitation b. Interspecies competition c. Parasitism d. Mutualism Answer: b. In interspecies competition, there is competition between two species for the same resources, which decreases the fitness of both species in many situations. 175.

What type of arrangement in a species involves behaviors intended to

increase the population’s fitness? a. Mutualism b. Commensalism c. Symbiosis d. Cooperation Answer: d. Cooperation is an intraspecies process that increases the population s fitness because of behaviors that exist between the different members. This is different from symbiotic relationships.

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176.

What happens in a mutualistic relationship, such as with honeybees and

flowers, when one species becomes extinct? a. The other species has no competition and it will become overpopulated. b. The surviving species selects another type of mutualistic organism. c. Nothing happens to the surviving species. d. The surviving species becomes extinct along with the first species. Answer: d. The surviving species, unless it can quickly evolve, will also become extinct because it is just as dependent on the other species as the extinct species is on the surviving species. 177.

What type of organism do humans have a mutualistic relationship with?

a. Malaria b. HIV c. Intestinal bacteria d. Body lice Answer: c. Intestinal bacteria and humans have a mutualistic relationship with one another. The others have a parasitic relationship with humans. 178.

The Red Queen Hypothesis applies to what type of relationship between

organisms? a. Parasite-host relationships b. Mutualistic relationships c. Intraspecies competitive relationships d. Cooperative group relationships Answer: a. The Red Queen Hypothesis applies to the host-parasite relationship because the organisms must adapt to the reciprocal adaptations of the other species.

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179.

With antagonistic coevolution of insects, what evolutionary characteristic

hasn’t been identified as something supporting reproduction? a. Females develop a thinner abdominal thorax for easier penetration. b. Females develop a storage area for sperm so they can self-inseminate. c. Males develop a longer sperm tail. d. Females evolve to be more aggressive in fending off insemination. Answer: a. The problem with female insemination with male sperm is that they get over-penetrated, which weakens them. Each of these things promote reproduction except or developing a thinner abdominal thorax because, in actuality, they don t want to have multiple penetrations. 180.

What plays the biggest role in determining what happens in mosaic

coevolution? a. Mutation rates b. Virulence of parasite c. Geographic variables d. Size of population Answer: c. With mosaic coevolution, geographic location of the two species in question determines the subtle differences in how each species coevolves with another. 181.

What is the main reason why infectious diseases have not been eradicated?

a. Natural selection favors antimicrobial resistance. b. Organisms increase their virulence over time. c. Humans have less resistance than they used to. d. New organisms are created that we aren’t immune to. Answer: a. Because of natural selection, drugs and vaccines are not as effective because pathogens become resistant to the drugs that have been developed. Many organisms are resistant to a number of antibiotics.

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182.

How can evolution explain the rise in heart disease and obesity-related

illnesses? a. We have evolved to become more overweight than our ancestors. b. We have evolved to be more sensitive to dietary fat and calories. c. We evolved to have an evolutionary advantage to procuring fatty food that is now too abundant. d. We have evolved to have lower basal metabolic rates than our ancestors. Answer: c. In the hunter-gatherer society, evolution favored those who could get and eat more but now that these things are plentiful, it has become an evolutionary disadvantage. 183.

What is not a human factor that contributes to the development of

zoonotic disease outbreaks? a. Having animals as pets b. Crowded population demographics c. Agricultural practices d. Lack of healthcare access Answer: a. Each of these is a reason for major diseases of zoonotic origin but having animals as pets is not one of these. 184.

Where did the Ebola virus come from originally?

a. Monkeys b. Insects c. Bats d. Fish Answer: c. Ebola came from fruit bats that later infected livestock that was eaten by humans to cause the Ebola virus disease in areas of the world with poor healthcare access.

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185.

Which human disease is evolutionarily the oldest?

a. HIV b. Leprosy c. Smallpox d. Malaria Answer: d. It is believed that malaria is one of the oldest diseases to have affected humans over the course of evolutionary time. 186.

What is true of genetics and disease resistance?

a. There are some people who do not get any infectious diseases to a great degree. b. There are some genes that protect against acute viral infections. c. There are random genes known to protect against specific diseases. d. There is no connection between genetics and infectious disease susceptibility? Answer: c. There are certain random genetic mutations that are known to protect against specific diseases but not all of the connections between genetics and infectious diseases have been discovered. 187.

How does the evolution of humans and pathogens help to prevent

pathogenic diseases in humans from killing the human race? a. Human evolution keeps up with bacterial evolution in an evolutionary arms race. b. Bacteria gradually lose their virulence over greater contact with humans. c. Humans make up for a lack of evolutionary responses with things like antibiotics. d. Evolution does not favor organisms that are pathogenic to humans. Answer: c. Human evolution does not keep up with bacterial evolution but the advances in antibiotics have made up for this lack of parity in the evolutionary processes.

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188.

What nutrient in particular is sequestered by humans during times of

infection to prevent bacteria from thriving within the human body? a. Selenium b. Iron c. Protein d. Glucose Answer: b. Iron is particularly necessary for bacteria to grow so humans have evolved to protect themselves by sequestering this nutrient away from bacteria. 189.

How would evolvability itself contribute to the aging phenomenon?

a. Old organisms do not reproduce so longevity is not selected for in the population. b. If older organisms dominate the gene pool, the species cannot evolve fast enough. c. Older organisms do not contribute to the longevity of the population. d. Evolvability does not contribute to the aging phenomenon. Answer: b. Evolution depends on reproduction so that, if older organisms dominate the gene pool, the species would not be able to evolve fast enough to keep up with selection pressures.

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190.

What is true of extrinsic and intrinsic mortality?

a. Predators have greater extrinsic mortality than intrinsic mortality. b. Larger organisms have greater extrinsic mortality than intrinsic mortality. c. Prey have a greater extrinsic mortality. d. Animals with fewer competitors have greater extrinsic mortality. Answer: c. The true statement is that prey have greater extrinsic or environmentally-caused mortality than they have intrinsic mortality. 191.

What makes up the greatest amount of the biomass of the earth?

a. Livestock b. Fish c. Humans d. Wild animals Answer: a. More than 60 percent of the biomass of the earth is made of livestock. The second largest group, making up about 30 percent, is humans. 192.

What habitat area has suffered the greatest devastation on flora and fauna

since the arrival of man? a. Rainforests b. Oceans c. Temperate areas d. Islands Answer: d. Because of their small size and nature, islands have suffered the greatest loss of flora and fauna because of the introduction of man into their habitat areas.

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193.

What feature of a virulent pathogen would least likely contribute to the

extinction of many animals with the introduction of the organism to a new area? a. It should affect many species. b. It should be very virulent with a high transmission rate. c. It should have a high mortality rate. d. It should lead to long-term chronic infections. Answer: d. An organism that would lead to mass extinction would have to kill quickly, kill many different organisms, and should kill most of the population over a short period of time with high virulence and transmission rates. 194.

What animal type is least threatened with extinction because of human

predation and loss of habitat? a. Bats b. Gorillas c. Rhinoceroses d. Big cat species Answer: a. These animal types are at the highest risk for defaunation and extinction, except for bats, which are more adaptable. 195.

What is true of human evolution?

a. We stopped evolving thousands of years ago. b. We have evolved to have bigger brains than thousands of years ago. c. The different races represent speciation of humans. d. Humans have evolved recently to adapt to their environment. Answer: d. Humans have been evolving but most of this has been physiological and has happened because of adaptation to the environment.

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196.

According to Darwinian theories on inheritance and natural selection,

which human trait or disease may decrease in humans because of natural selection? a. Intelligence b. Tourette’s syndrome c. Alcoholism d. ADHD Answer: a. Each of these things is believed to possibly increase over time, except that intelligence could decline if people with less intelligence have more children. This has not been proven to be the case so far. 197.

In evolution, what is omnicide?

a. Death to humans from natural disasters b. Death to reproductive-age humans c. Decrease in fertility rates in humans d. Extinction of humans through human activities Answer: d. Omnicide involves the extinction of the human race because of human-related activities, such as biological or nuclear warfare, or ecological disasters. 198.

What has not yet occurred as part of global warming of the earth?

a. Extreme weather events b. Evaporation of the ocean c. Changes in season timing d. Loss of polar ice caps Answer: b. Each of these has occurred except that the oceans have not begun to evaporate as a result of global warming.

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199.

What is true of precipitation events during global warming?

a. All areas of the world will dry out. b. All areas of the world will be wetter. c. Wet areas will be drier and dry areas will be wetter. d. Wet areas will be wetter and dry areas will be drier. Answer: d. With global warming, there will not be an equalization of precipitation. Dry areas will become drier and wet areas will become wetter. 200. What most likely contributes to the rise in sea levels so far? a. Loss of polar ice caps b. Thermal expansion of the oceans c. Loss of Greenland ice sheets d. Glacier losses Answer: b. The thermal expansion of the oceans has contributed to more than 70 percent of the rise in the sea levels so far.

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College Level Evolution

Articles inside

Course Questions and Answers

Summary

Key Takeaways

Quiz

Future of the Planet with Global Warming

Human Extinction

Ways Humans Might Evolve

Quiz

Evolution of Senescence

Host and Pathogen Evolution

Disease Susceptibility

Quiz

Key Takeaways

Mosaic Coevolution

Antagonistic Coevolution

Host-Parasite Coevolution

Quiz

Key Takeaways

Coevolution and Mutualism

Cooperation in Populations

Group Living

Hardy-Weinberg Model

Quiz

Key Takeaways

Sex and Mate Selection

Mating Systems

Quiz

Evolution of Sexual Reproduction

Key Takeaways

Mass Extinction

Background Extinction

Quiz

Key Takeaways

Evolution before the Homo Genus

Modern Human Evolution

Evidence for Human Evolution

Evolution of the Homo Genus

Human Migration

Human Structural Changes

Human Evolution

Quiz

Key Takeaways

Speciation and Modes of Speciation

Genetics of Speciation

Quiz

Key Takeaways

Transition to Group Living

Evolution of Individuality

Origin of Eukaryotes

Evolution of Multicellularity

Prokaryotic Cell and Eukaryotic Cell Evolution

Quiz

Viral Evolution

Early Forms of Life

Quiz

Key Takeaways

Genetic Processes

Genetic Variability and Mutation

History of Genetics

Mendelian Genetics

Mutations

Quiz

Key Takeaways

Phylogenetics and Molecular Phylogenetics

Adaptation, Fitness, and Reproductive Success

Phylogenic Trees

Key Takeaways

Quiz

Cladistics

Quiz

Key Takeaways

The Story of Darwin

Evolutionary Thought in Ancient Times

Nineteenth Century Evolution

Christian Philosophies on Evolution

Preface

Timeline of Evolutionary Theories

After Darwin and Natural Selection