Andreas Wagner in Aeon:
Classification requires comparison. In the process, we see how deeply similar the legs of birds and lions are, or the flowers of roses and marigolds. Such resemblances form a cornerstone of Darwin’s great insight that all life forms a grand family. Yet scientists such as Cuvier rejected the idea of evolution’s great chain of living beings, drawing support from the large gaps that then existed in the fossil record. ‘If the species have changed by degrees,’ he wrote in 1827, ‘we should find some traces of these gradual modifications.’ If he had seen the intermediate steps that we have now seen, perhaps he would have changed his mind.
But perhaps not. For the reasons to reject evolution go deeper than incomplete knowledge. In fact, we can follow them all the way back to Plato, whose influence looms so large that the 20th-century thinker Alfred North Whitehead could relegate the entirety of European philosophy to a ‘series of footnotes’ to his work.
For Plato, the perceptible material world is like a faint shadow of a higher reality. What really matters is the realm of abstract concepts. To a Platonist, the essence of soccer balls, golf balls and tennis balls is their ball-like shape. It is this pure, abstract and unchanging essence that is real, not the physical balls, whose existence is as fleeting and impermanent as a shadow.
A systematist’s task might be daunting, but it becomes manageable if each species is distinguished by its own Platonic essence. For example, a legless body and flexible jaws might be part of a snake’s essence, different from that of other reptiles. The task is to find a species’ essence. Indeed, the essence really is the species in the world of Platonists. To be a snake is nothing other than to be an instance of the form of the snake.
The only problem: the glass lizard. And hundreds of other creatures that defy easy categorisation, such as Eupodophis, from the late Cretaceous period, a snake with rudimentary hind legs. In an ever-changing Darwinian world, species incessantly spew forth new species whose traits can shade into one another. The 20th-century biologist Ernst Mayr called Plato the ‘great antihero of evolutionism’, and in fact it was Mayr who replaced the essentialist concept of species with a modern biological alternative, based on individuals in the same population that can interbreed.
But as has happened many times before, Plato might have the last word. We just need to look deeper than the ephemeral appearance of living things.