THE THEORY of evolution through natural selection, discovered independently by Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913), is the central organising theory in biology. While there is general agreement among scientists on the broad outlines of how evolution works, many important details remain to be worked out. For example, most biologists believe chance plays such a major role that, if evolution were to run its course again, the range and nature of biological organisms it would produce would be radically different to what we see on Earth today, writes WILLIAM REVILLE
On the other hand, some scientists point to the phenomenon of convergence in evolution and argue that the emergence of the various biological properties, including human-level intelligence, is inevitable. Convergence is the recurrent evolutionary tendency of very different organisms to find the same "solution" to a particular "need". Convergence and its implications are vividly described by Simon Conway Morris in Life's Solution: Inevitable Humans in a Lonely Universe(Cambridge University Press, 2005). Conway Morris is professor of evolutionary palaeobiology at the University of Cambridge and he is renowned for his ground-breaking work on the fossils of the Burgess Shale, one of the most important fossil finds ever.
Evolution is understood to operate through chance and necessity. New biological characteristics arise by random genetic mutations and those that are best suited to the environment, survive, and those not suited perish (natural selection).
Stephen Jay Gould in his popular book Wonderful Life: The Burgess Shaleand the Nature of History (WW Norton, 1990) memorably remarked that if you rewound the tape of evolution and played it again you would end up with a radically different result to what we currently see. In particular Gould argued that human intelligence would almost certainly not arise in the re-run. On the other hand, Conway Morris argues that a re-run of the tape would produce very similar results to what we see today.
Conway Morris visualises the biological realm as a vast sea sparsely dotted with islands. The vast empty oceans represent all the possible biological forms that do not work and that therefore will not be chosen by natural selection, and the islands are the forms that work – islands of biological adaptation. Evolution is the search engine that finds the islands, and it is remarkably efficient at finding a particular island no matter from where it starts on the vast ocean.
Convergent evolution is the process whereby the same biological trait is developed in unrelated lineages – or, in other words, how very different organisms “navigate” to the same biological solution from very different starting points. The camera-eye of the vertebrate is a classical example. The camera-eye of the vertebrates (eg humans), cephalopods (eg octopus) and cnidarea (eg box jelly fish), are remarkably similar, but they evolved completely independently. Similarly impressive examples of convergence are described by Conway Morris in the areas of hearing, olfaction, balance, echolocation, and in many more instances.
For example, consider locomotion. The adaptive islands that facilitate locomotion in biology are mainly legs, fins, wings, and slithering, but no wheels are seen, which are so ubiquitous in our civilised world. The reason is that, as life was evolving, the solid surfaces to be negotiated were muddy, oozy, tangled and hopelessly uneven, so wheels would quickly get bogged down. Hence the convergence from all quarters towards legs, fins and wings, depending on the environment to be negotiated.
Conway Morris sees convergence in the evolution of intelligence. The main intelligent groups are the anthropoid apes, elephants, cephalopods (eg octopus and squid), whales and dolphins, and some birds, particularly Caledonian Crows. Conway Morris draws attention to convergence in the neurological basis for this intelligence.
Humans have a greater level of intelligence than any other species and also a unique sophisticated language. He believes the intelligence we possess was inevitable and if we had not evolved to become tool-using bipedals another primate species would have done so.
The world of human intelligent civilisation is an island of adaptation on the vast ocean that would be inevitably found by the great search engine of evolution.
In other words, we humans, or something very like us, are meant to be here. This is a radically different conclusion to the mainline Darwinian interpretation that humanity has emerged completely by accident. Conway Morris also expects that extraterrestrial life, if it exists, looks quite like the familiar forms we see on Earth.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC – http://understandingscience.ucc.ie