Читать книгу The Evolution of Everything: How Small Changes Transform Our World - Matt Ridley, Matt Ridley - Страница 21

Nearly six decades after Paley’s book, Charles Darwin’s produced a comprehensive and devastating answer. Brick by brick, using insights from an Edinburgh education in bottom–up thinking, from a circumnavigation of the world collecting facts of stone and flesh, from a long period of meticulous observation and induction, he put together an astonishing theory: that the differential replication of competing creatures would produce cumulative complexity that fitted form to function without anybody ever comprehending the rationale in a mind. And thus was born one of the most corrosive concepts in all philosophy. Daniel Dennett in his book Darwin’s Dangerous Idea compares Darwinism to universal acid; it eats through every substance used to contain it. ‘The creationists who oppose Darwinism so bitterly are right about one thing: Darwin’s dangerous idea cuts much deeper into the fabric of our most fundamental beliefs than many of its sophisticated apologists have yet admitted, even to themselves.’

The beauty of Darwin’s explanation is that natural selection has far more power than any designer could ever call upon. It cannot know the future, but it has unrivalled access to information about the past. In the words of the evolutionary psychologists Leda Cosmides and John Tooby, natural selection surveys ‘the results of alternative designs operating in the real world, over millions of individuals, over thousands of generations, and weights alternatives by the statistical distribution of their consequences’. That makes it omniscient about what has worked in the recent past. It can overlook spurious and local results and avoid guesswork, inference or models: it is based on the statistical results of the actual lives of creatures in the actual range of environments they encounter.

One of the most perceptive summaries of Darwin’s argument was made by one of his fiercest critics. A man named Robert Mackenzie Beverley, writing in 1867, produced what he thought was a devastating demolition of the idea of natural selection. Absolute ignorance is the artificer, he pointed out, trying to take the place of absolute wisdom in creating the world. Or (and here Beverley’s fury drove him into capital letters), ‘IN ORDER TO MAKE A PERFECT AND BEAUTIFUL MACHINE, IT IS NOT REQUISITE TO KNOW HOW TO MAKE IT.’ To which Daniel Dennett, who is fond of this quotation, replies: yes, indeed! That is the essence of Darwin’s idea: that beautiful and intricate organisms can be made without anybody knowing how to make them. A century later, an economist named Leonard Reed in an essay called ‘I, Pencil’, made the point that this is also true of technology. It is indeed the case that in order to make a perfect and beautiful machine, it is not requisite to know how to make it. Among the myriad people who contribute to the manufacture of a simple pencil, from graphite miners and lumberjacks to assembly-line workers and managers, not to mention those who grow the coffee that each of these drinks, there is not one person who knows how to make a pencil from scratch. The knowledge is held in the cloud, between brains, rather than in any individual head. This is one of the reasons, I shall argue in a later chapter, that technology evolves too.

Charles Darwin’s dangerous idea was to take away the notion of intentional design from biology altogether and replace it with a mechanism that builds ‘organized complexity … out of primeval simplicity’ (in Richard Dawkins’s words). Structure and function emerge bit by incremental bit and without resort to a goal of any kind. It’s ‘a process that was as patient as it was mindless’ (Dennett). No creature ever set out mentally intending to see, yet the eye emerged as a means by which animals could see. There is indeed an adapted purposefulness in nature – it makes good sense to say that eyes have a function – but we simply lack the language to describe function that emerged from a backward-looking process, rather than a goal-directed, forward-looking, mind-first one. Eyes evolved, Darwin said, because in the past simple eyes that provided a bit of vision helped the survival and reproduction of their possessors, not because there was some intention on the part of somebody to achieve vision. All our functional phrases are top–down ones. The eye is ‘for seeing’, eyes are there ‘so that’ we can see, seeing is to eyes as typing is to keyboards. The language and its metaphors still imply skyhooks.

Darwin confessed that the evolution of the eye was indeed a hard problem. In 1860 he wrote to the American botanist Asa Gray: ‘The eye to this day gives me a cold shudder, but when I think of the fine known gradation my reason tells me I ought to conquer the odd shudder.’ In 1871 in his Descent of Man, he wrote: ‘To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.’

But he then went on to set out how he justified the absurdity. First, the same could have been said of Copernicus. Common sense said the world stood still while the sun turned round it. Then he laid out how an eye could have emerged from nothing, step by step. He invoked ‘numerous gradations’ from a simple and imperfect eye to a complex one, ‘each grade being useful to its possessor’. If such grades could be found among living animals, and they could, then there was no reason to reject natural selection, ‘though insuperable by our imagination’. He had said something similar twenty-seven years before in his first, unpublished essay on natural selection: that the eye ‘may possibly have been acquired by gradual selection of slight but in each case useful deviations’. To which his sceptical wife Emma had replied, in the margin: ‘A great assumption’.