The Ancestor's Tale by Richard Dawkins

A pilgrim's progress

Yes!" squeaks the star-nosed mole, clapping his spades with excitement. "No, it won't do," Richard Dawkins rules, silencing the diminutive mammal after one short paragraph. He can't bring himself to make his creatures tell their own tales. Not that Dawkins has anything in principle against animals talking in books: one of his childhood influences was Doctor Dolittle, which instilled a lasting sense that human ethics are loaded against other species. It's just that his one authentic voice is his own: what we look forward to hearing when we open a new Dawkins book.

The tone this time is different. Dawkins has already expounded the arguments that form his vision of life, both in the natural and human realm. Now, having risen from the Bar to Bench, he is in a position to offer himself as judge and senior guide. In The Ancestor's Tale, he has become the kind of teacher without whom childhood nostalgia is incomplete: unflagging in his devotion to enlightenment, given to idiosyncratic asides. His mission is to tell the story of the origin of species backwards, with a framework borrowed from the Canterbury Tales, as a procession back to the beginning of life joined by streams of "pilgrims".

This requires him to counterbalance his scientific instincts, which have always encouraged him to concentrate on theory, with a more classical stewardship of biological details. It also entails comprehensive colour illustration and a spacious format that leaves nice margins to show off the asides.

Stephen Jay Gould, an evolutionary advocate of a different stripe, might have had sport discussing whether the latter feature should be seen as accident or adaptive design. Such questions defined the differences Gould had with "ultra-Darwinists". In one of his asides, Dawkins trumps that taunt as "a slander I would protest more vigorously if the name sounded less of a compliment than it does".

He is not, in any case, in a confrontational mood. By its nature this book covers ground already trodden, and Dawkins is generous with references to other people's books. He is also concerned to give credit where due: to his research assistant Yan Wong, for sections of the text, to Nicky Warren, who thought up the handy term "concestors" for the common ancestors on which lineages converge. The effect is to evoke the collegial ideal of science and its collective nature.

That is what The Ancestor's Tale is fundamentally about. It doesn't really seek to contemplate deep time or the indefinite complexity of a single organism, and looks no further to literature than the Chaucerian device. What fires Dawkins and sustains him are biological problems and the work of solving them.

Why do we have such large brains and walk upright? Why is sex almost everywhere in nature, when reproduction would be so much less trouble without the need for mates? And how on earth are all these myriad living forms related to each other? This latter question looms large, as Dawkins puzzles over the route he has obliged himself to take. The result is not just a wealth of ideas about how living things evolved, but a strong sense of the urgency and absorption with which science is done.

Nobody ever said that a pilgrimage is supposed to be one long party, and Dawkins's candour is welcome at the point where he admits "there is not a lot to describe" about flatworms. Long marches may have their false starts too, as when, in his one sustained discussion of social issues, he takes the tendency to see anybody with any noticeable African features as "black" to be a universal psychological trait rather than a choice forced by the weight of history. But who'd want to go on a long journey with somebody who was always right and never personal? The success of this book comes from having one truly Chaucerian character: the author himself.

Marek Kohn's 'A Reason for Everything' is published by Faber& Faber.

Richard Dawkins appears at the Cheltenham Festival of Literature on Monday 11 October. (01242 227979; www.cheltenhamfestivals.co.uk)

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