Mount Improbable does not exist on any map. For Richard Dawkins, the world’s leading champion of Darwinian theory, it is the metaphorical obstacle which every living organism must negotiate to evolve successfully.

Such intricately ‘designed’ structures as the spider’s web and the snail’s shell are, he argues, examples of ingenious ascents to evolutionary heights – in which chance plays a powerful part.

To demonstrate this, Richard Dawkins turns to nature’s complex achievements: the elephant’s trunk, adapted as its environment changed; the bolas spider which mimics the perfume of the female moth to lure male moths for food; the starshaped evening primrose that guides insects to its nectar and pollen.

Each of these evolutionary successes was made possible by a long, slow pilgrimage rather than by sudden leaps. Writing with clarity and gusto, Richard Dawkins goes where Darwin feared to tread, even explaining how the eye evolved in 40 different species. Often quirky, sometimes confounding but always compelling, Climbing Mount Improbable is a tour de force.

NOT JUST A THEORY - JOHN GRIBBIN

John Gribbin, author of History of Western Science, pays tribute to Richard Dawkins, who has devoted his career to increasing the world’s understanding of evolution.

Richard Dawkins is the best writer on the mechanism of evolution since Charles Darwin himself. He has also had the patience and stamina to act as a spokesman for science, particularly on the matter of evolution, in the face of a seemingly wilful public ignorance of what science is all about. In this context, it is particularly relevant that his books, such as Climbing Mount Improbable and The Blind Watchmaker, are indeed about the mechanism of evolution, not whether or not evolution actually happens.

Evolution is a fact, like the fact that apples fall off trees. This was already well known in Darwin’s day – indeed, his grandfather, Erasmus Darwin, was one of the earlier thinkers who puzzled over the fact of evolution before Charles Darwin was even born, and tried to find a mechanism to account for it. The mechanism that does account for it is natural selection, which was hit upon independently by Charles Darwin and Alfred Russel Wallace from their separate studies of the proliferation of life in the tropics and the ‘struggle for survival’.

Natural selection is the theory that explains the fact of evolution, just as the general theory of relativity is the theory that explains the fact of gravity – the reason why, among other things, apples fall off trees.

This terminology highlights another important feature of the scientific endeavour which emerges so clearly from Dawkins’s lucid prose. People who criticise the idea of evolution often do so partly on the grounds that it is ‘just a theory’. Leaving aside the fact that the theory is natural selection, not evolution, what matters is that they have been confused by the difference between the use of the word ‘theory’ in everyday language and its use in a scientific context. In everyday language, someone’s half-baked idea might be described as ‘just a theory’ – my brother reckons that the right way to add milk to tea is to pour the milk first, but that’s just his theory, and I’m entitled to my own opinion. In science, a theory is a fully baked idea that has been tested by experiment and observation, and passed those tests.

Even if, or when, it fails a test, a successful theory need not be completely discarded, because any new theory that supersedes it must pass all the tests the older theory passed, as well as the new tests. In this way, Newton’s theory of gravity did not become irrelevant when Einstein’s theory of gravity came along. Newton’s theory still works well for describing the way apples fall from trees; Einstein’s theory also explains that, but in addition it explains details of, for example, the orbit of the planet Mercury, which Newton’s theory cannot explain.

Natural selection has been seen at work all around us – in one of the most beautiful and apposite examples, in the populations of finches on the Galapagos Islands, where Darwin himself marvelled at what he saw. Jonathan Weiner’s book The Beak of the Finch goes into absorbing detail on this. Natural selection has also been seen at work in laboratory experiments, with creatures such as fruit flies which have short lifespans and can be studied over many generations.

The other objection to the idea of evolution by natural selection, often made from a position of ignorance, can be summed up as: ‘What use is half an eye?’ In other words, how could a complex organ like the eye have evolved by a series of small steps, as evolution by natural selection requires. The quick answer is that half an eye can be very useful indeed, and certainly better than no eye at all when you are being threatened by a predator. The long answer, how eyes can evolve step by step, starting from a patch of lightsensitive cells on the skin, is spelled out in Climbing Mount Improbable.

This is a classic example of what Dawkins’s title is all about – you don’t get to the top of a mountain in one leap, but by following a long and gentle path to the summit. If you see a picture of a person on top of a mountain, you don’t assume they got there by magic, or through a miraculous intervention by God, but that they climbed up step by step. So it is with eyes and other complex organs. Eyes are so valuable, in fact, that they have evolved at least forty separate times, following forty different winding paths to this particular mountain top.

And then there’s the question of randomness. The small changes that add up to make an eye, or anything else, are produced at random. So how can they add up to make something meaningful? Because, as Darwin realised, although the changes are andom, the selection is not.This is the whole point of what is sometimes called Darwinian evolution. Only beneficial changes enhance the ability of the organism to survive and reproduce, passing on those benefits to future generations. Here, another of Dawkins’s skills comes to the fore. His computer simulations, which you can run in the privacy of your own PC, demonstrate evolution by natural selection at work before your very eyes, and show how random changes plus selection can produce complex results. This is the modern equivalent of Darwin’s own demonstration of the process by breeding pigeons.

Richard Dawkins is set to retire this year from his post as Simonyi Professor for the Public Understanding of Science, having reached the University of Oxford’s mandatory retirement age. We can only hope that this so-called ‘retirement’ will actually give him more time to delight us with books like Climbing Mount Improbable.

Climbing Mount Improbable by Richard Dawkins, or History of Western Science by John Gribbin are available to order online. You may also be interested in Dawkins' The Blind Watchmaker, The Selfish Gene and Unweaving The Rainbow.