The Dead Hand of Plato
In his book “The Greatest Show on Earth”, Dawkins argues that while evolution is real it is also hard to understand. People think in categories. Yet, categories do not exist - and the belief in them makes reality harder to understand. He argues that essentialism, which he calls “the dead hand of Plato”, is what keeps people from understanding evolution.
Human language divides animals into different species, although species of animals no not exist in physical reality. In physical reality (which Dakwins calls simply "reality"), only individual animals exist.
In the platonist worldview, each individual animal is nothing more than a shadow of the “idea” of the species. This worldview shackles our understanding of animals into monolithic concepts of species, thus making it impossible for us to understand transitions and intermediate forms – when the truth is that every animal that exists is a transitional form, and that the division into species is more or less arbitrary.
By this argument, Dawkins is indirectly making a strong case for Social Constructionism being highly relevant not only in social science but also in natural science: While our concepts doesn't exist in physical reality, they do affect – and in some cases distort – our perception of this same physical reality. We must therefore keep ourselves aware of them.
Categories are a central part of human lived experience. Dawkins' notion that categories doesn't exist may thus be hard to understand, unless we make a clear distinction between different layers of reality.
From "The Greatest Show On Earth", page 13. (Chapter 2, sub-chapter "The Dead Hand of Plato".)
For Plato, the 'reality' that we think we see is just shadows cast on the wall of our cave by the flickering light of the camp fire. Like other classical Greek thinkers, Plato was at heart a geometer. Every triangle drawn in the sand is but an imperfect shadow of the true essence of triangle. The lines of the essential triangle are pure Euclidean lines with length but no breadth, lines defined as infinitely narrow and as never meeting when parallel. The angles of the essential triangle really do add up to exactly two right angles, not a picosecond of arc more or less. This is not true of a triangle drawn in the sand: but the triangle in the sand, for Plato, is but an unstable shadow of the ideal, essential triangle.
Biology, according to Mayr, is plagued by its own version of essentialism. Biological essentialism treats tapirs and rabbits, pangolins and dromedaries, as though they were triangles, rhombuses, parabolas or dodecahedrons. The rabbits that we see are wan shadows of the perfect 'idea' of rabbit, the ideal, essential, Platonic rabbit, hanging somewhere out in conceptual space along with all the perfect forms of geometry. Flesh-and-blood rabbits may vary, but their variations are always to be seen as flawed deviations from the ideal essence of rabbit.
How desperately unevolutionary that picture is! The Platonist regards any change in rabbits as a messy departure from the essential rabbit, and there will always be resistance to change - as if all real rabbits were tethered by an invisible elastic cord to the Essential Rabbit in the Sky. The evolutionary view of life is radically opposite. Descendants can depart indefinitely from the ancestral form, and each departure becomes a potential ancestor to future variants.
For the mind encased in Platonic blinkers, a rabbit is a rabbit is a rabbit. To suggest that rabbitkind constitutes a kind of shifting cloud of statistical averages, or that today's typical rabbit might be different from the typical rabbit of a million years ago or the typical rabbit of a million years hence, seems to violate an internal taboo. Indeed, psychologists studying the development of language tell us that children are natural essentialists. Maybe they have to be if they are to remain sane while their developing minds divide things into discrete categories each entitled to a unique noun. It is no wonder that Adam's first task, in the Genesis myth, was to give all the animals names.
To dramatize how very anti-essentialist evolution is, consider the following. On the 'population-thinking' evolutionary view, every animal is linked to every other animal, say rabbit to leopard, by a chain of intermediates, each so similar to the next that every link could in principle mate with its neighbours in the chain and produce fertile offspring. You can't violate the essentialist taboo more comprehensively than that. And it is not some vague thoughtexperiment confined to the imagination. On the evolutionary view, there really is a series of intermediate animals connecting a rabbit to a leopard, every one of whom lived and breathed, every one of whom would have been placed in exactly the same species as its immediate neighbours on either side in the long, sliding continuum. Indeed, every one of the series was the child of its neighbour on one side and the parent of its neighbour on the other. Yet the whole series constitutes a continuous bridge from rabbit to leopard - although, as we shall see later, there never was a 'rabbipard'. There are similar bridges from rabbit to wombat, from leopard to lobster, from every animal or plant to every other.