Discuss the role of chance in evolution

        Evolution has been shaped by more than just mutations. There have been many chance events over the course of history that have had a profound effect on species diversity. Mass extinctions are a key example in this, where selection does not involves fitness levels but occurs randomly, affecting species and lineages. If these events did not occur then there may not be the level of diversification we see on the Earth today.

        The evolution of organisms has been a result of a long chain of contingences, where each step in the process has been an improvement on the last leading to highly developed structures and processes within organisms. The theory of the evolution of the eye is an excellent example of this, where the flat layer of light-sensitive cells slowly developed. The first major step was the curving of the photoreceptive layer, causing it to become concave which allowed more photo receptors to fit in. Then a lens formed which aided in the refraction of the light in order for the light to be focussed on the photoreceptive layer. Evidence to support this theory is found when other organisms eyes are examined which show the intermediate stages in the evolution of the eye, such as the eyes of molluscs. Homo sapiens were also the result of cumulative changes. If events that shaped the way we have turned out had occurred any differently then we in turn as a species would probably be very different. This shows that although it is not a truly random process that shapes such structures as the eye, the path which organisms have taken is unpredictable and cannot be replayed with the same result. There is no scientific evidence that humans' existence was inevitable or that evolution in general has any predetermined goals.

        There is some evidence that evolution is not as random as some may think. If you take the example of whales and dolphins for example it can be seen that although these two species are from different lineages, the fish and cetacean, they share the same streamline body shape. This shape developed due to it being the most efficient shape for movement in the water. The shape must have therefore developed separately in an example of an evolutionary phenomenon called convergence, precisely because it is the best shape for that environment regardless of what kind of creature has it. If evolution were random, we would not see this kind of predictable pattern.

        Some scientists, such as Masatoshi Nei, believe that mutations are the ‘driving force of evolution at the molecular level’, that they are the limiting factor. The idea that populations of organisms contain the necessary variations in order for natural selection to be the only force required for evolution has been challenged, increasing the role of chance within evolution.

        Jacques Monod voiced that ‘chance alone is at the source of every innovation, of all creation in the biosphere. Pure chance, absolutely free but blind…’ It is hard to find evidence to support this theory, as natural selection must still play a huge role in determining how genes are past on and therefore how organisms develop. The process of evolution is driven by the engine of natural selection, a filter that extracts order out of chaos according to a fixed and non-random set of rules. If there were no selection, change in living things would follow a pattern called a "random walk". There would be no permanent change in gene frequency across generations.

        In conclusion, evolution does contain a component of chance, but there is far more to the process than that, and it is precisely the existence of the non-chance components that allows evolution to work. Evolution will not proceed in just any direction, but only in those that make them better adapted to their surroundings.