BOOKS: All in a geological blink

"AND a river went out of Eden to water the garden" (Genesis 2:10). And the river was DNA, in Richard Dawkins's metaphor. It was and is a river of genes, of "pure information", flowing through time, not space, branching periodically to produce new species.

"Life is just bytes and bytes and bytes of digital information... Every cell in your body contains the equivalent of 46 immense data tapes [the chromosomes], reeling off digital characters via numerous reading heads working simultaneously." These characters consist of four chemical "letters" that make up the long strands of DNA, and occur identically in all living things: bacteria, brussels sprouts, human beings. They differ only in the way they are arranged.

There's no knowing why the universe exists at all, and it's still hard to see how DNA itself evolved. But once DNA is in place there is no special mystery in living creation (the existence of consciousness is more of a problem for physics than for biology). Darwin's theory of evolution by natural selection promises to explain it all - the complexity, elegance and savagery of nature. Given the theory, the remaining task is simply to work out the footnotes, the details, in the light of a modern understanding of genetics - how the eye evolved, or the feeling of loyalty, or the peacock's tail, or the "waggle dance" of bees.

River Out of Eden is based on lectures originally given to children, but Dawkins turns it into something more than that. He lays out the basics of modern genetics and the theory of evolution with his usual expository ingenuity and style, varying and developing themes from his earlier books The Selfish Gene (1976, new edition 1989), The Extended Phenotype (1982) and The Blind Watchmaker (1986). At the same time he adds new material - as in his elegant account of "African Eve", or, as he prefers to all her, "Mitochon-drial Eve", a single female from whom all human beings alive today can be shown to be descended, and who lived no more than 150,000 to 250,0000 years ago. Dawkins corrects a number of misconceptions about her, pointing out, for example, that it is hugely unlikely that she is our most recent common ancestor.

Dawkins also returns to the subject of the eye, which he discussed in The Blind Watchmaker. When we consider something as exquisitely structured as the human eye, we find it hard to believe that it could have evolved gradually. We can't believe that there could have been enough time for this to happen. The Blind Watchmaker showed how hopelessly bad we are at acquiring a genuine imaginative grasp of just how much time there has been; River Out of Eden contains a nice addendum. He points out that "the" eye has evolved separately at least 40 times, and draws on recent computer simulations of evolution to show that (on plausible assumptions) there has in fact been far more time than is needed for something like the human eye to have evolved. Assuming typical generation lengths for the small animals who were our ancestors, "the time needed for the evolution of the eye, far from stretching credulity with its vastness, turns out to be too short for geologists to measure! It is a geological blink."

River Out of Eden is always clear, but it requires concentration. It is a passionate book, and Dawkins sometimes expresses his irritation with those who deny the theory of evolution. This risks being counterproductive, but it is understandable, for there can be no serious doubt about the theory's truth. Dawkins is particularly impatient with those who continue to believe in an omnipotent and loving God, when "the total amount of suffering per year in the natural world is beyond all decent contemplation". Such a belief appears to require a strange callousness, and in his general attitude to religion Dawkins seems to agree with Freud's view in "Civilisa- tion and its Discontents": "The whole thing is so patently infantile, so incongruous with reality, that to one whose attitude to humanity is friendly it is painful to think that the great majority of mortals will never be able to rise above this view of life."