Paelozoology Will Clark Upper Sixth
Charles Darwin
Throughout the evolutionary history of animals, there have been many integral driving forces that have combined to push animals to the evolutionary point they are at today, with millions of complex organisms deriving from once singlecelled organisms inhabiting the Earth. Each of these driving forces has certainly been integral and essential in its own right, making it difficult to pinpoint a “most influential” factor. It is unlikely that any of these developments could have happened without the others happening. However it is fair to say that some factors, such as mitochondria being absorbed into eukaryotic cells, has a distinctly more noticeable physical advantage than a factor such as the predator-prey relationship, as this is more of a behavioural evolutionary trait, compared to the drastic physical changes caused by the engulfment of mitochondria by eukaryotes. The symbiotic relationship formed as this event happened helped shape the modern cells as we study them today. Therefore it is a factor that cannot be overlooked and is clearly monumentally important in the development of animals. However, another factor that is perhaps often overlooked is the ability to reproduce sexually, and the numerous advantages this trait brings with it. Sexual reproduction is one of the most complex and bizarre scientific processes we can study, and the creation of a new
lifeform that is genetically unique from its predecessor brings some serious advantages in the evolutionary game, helping modern animals to push through the evolutionary boundaries that other lifeforms have faced. The origin of sexual reproduction is widely disputed, with the first species to utilise this evolutionary tool being highly uncertain. Despite 99.99% of eukaryotes being known to reproduce sexually as opposed to asexual reproduction, we still do not know exactly how and why this process first came about. One argument for the origin of sexual reproduction states that organisms simply engage in sexual reproduction as opposed to asexual as it is pleasurable. However, on the large-scale evolutionary picture, this theory seems rather out of place and far-fetched. Considering that the first eukaryotic organisms to engage in sexual reproduction were single-celled protists that appeared over two billion years ago, this argument starts to seem rather unlikely. This is further confirmed when considering the fact that organisms capable of producing pleasure-inducing neurons only evolved around 1.3 billion years ago, casting doubt on the pleasurable aspect of sexual reproduction for this 700-million-year period. The eukaryotic cells that engaged in sexual reproduction in this time tended to transfer genetic material via processes such as conjugation, transformation and transduction, all of which come under the umbrella of parasexuality.
adapt to their environments, as natural selection does. However, as I will discuss later, producing more variable offspring is not always favourable, and, even more surprisingly, sexual reproduction does not always increase the variability among the offspring. Although the dawn of sexual reproduction has always been a puzzle for scientists, it seemed to puzzle no one more than Darwin himself. Although making breakthroughs in the areas of natural selection and evolutionary studies, he wrote in 1862: “We do not even in the least know the final cause of sexuality; why new beings should be produced by the union of the two sexual elements. The whole subject is as yet hidden in darkness.” He could not explain the reasons why many organisms and animals will go to great and troublesome lengths to attract a mate and be completely preoccupied by sex, even if it is time consuming and troublesome for the creature. Why would animals make the transition from asexual reproduction, a form that is known to be far more efficient and less troublesome, to sexual reproduction, a time consuming and often unpredictable lottery of creating a new generation? This can partly be explained again by August Weismann’s theory of “individual differences” upon which natural selection acts. Reproducing sexually causes the offspring to carry a
Sexual reproduction is one of the most complex and bizarre scientific processes.
Another theory as to the original reason that sexual reproduction was brought into the behaviour of modern animals states that it is because of its ability to produce genetically variable offspring, allowing natural selection to take its course. This is a far more reasonable theory, and dates back to the work of German biologist August Weismann in the late 1800s. It is natural that organisms would reproduce in a way that best lets them evolve and 24
