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
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