Richard Dawkins

THE ANCESTOR'S TALE

A pilgrimage to the dawn of life

Most popular books on evolution begin in the past and move forward to the present, but this can all too easily cause unwary readers to suppose that there is something like a ladder of increasing perfection leading inevitably to humans. Dawkins therefore had the good idea of telling the story in reverse, beginning with humans and working backwards. And he has done this by loosely adopting the format used by Geoffrey Chaucer in the Canterbury Tales. Various living species are imagined as pilgrims in time and each is made to tell its own tale. By this means we trace the branching sequence of evolution back in time. As we do so we encounter "rendezvous", which are nodes where we find the hypothetical common ancestor ("concestor") which links the lineage in question to the main evolutionary tree.

This idea might seem like a gimmick, and it could easily have misfired in the hands of a less experienced writer, but Dawkins has brought it off with considerable success. The literary device of the tales is not allowed to become intrusive or a constraint; rather, each tale is a jumping-off point from which Dawkins can digress to expound his ideas at whatever length he wishes. And although The Ancestor's Tale is full of illustrations, including reconstructions of the imagined "concestors", it is more than a coffee-table book; there is no attempt to avoid areas of uncertainty where these exist and some topics are discussed in a fair amount of depth. These include the evolution of sex and of different kinds of symmetry, hox genes, and (one of my long-term favourites) the suggestion that vertebrates are really upside-down invertebrates, with reversal of the arrangement of their main nerve trunk and circulatory system.

In principle, the story could begin with any species, since everyone comes together in the end, but because Dawkins is writing for humans he starts with us and the early tales are told by our near relatives. (Dawkins bends the rules a little here to allow extinct species such as the Neanderthals to appear.) From this point we travel farther back in time, as we are joined progresssively by the great apes, monkeys, tarsiers, lemurs and so on. At first the pace is comparatively leisurely but later things speed up as we leave the mammals and meet amphibians, fish, and ultimately less familiar kinds of organism, until finally we go beyond the bacteria and get right back to the mysterious origin of life itself in deep time. This narrative approach gives a vivid sense of the extreme diversity of life together with its underlying unity.

Dawkins is decisive in rejecting the idea that evolution is in any sense directed, but he does acknowledge that something like patterns may be discerned, rather in the way suggested by Stuart Kauffman. If the "tape" of evolution could be rerun, would it follow something like the same course or would it be quite different? Dawkins is impressed by the evidence from convergent evolution, which suggests that life may be constrained by its environment in the forms it can take; only a particular range of possibilities seems to be available. I specially enjoyed his speculation about what might happen following a major extinction like that which eliminated the dinosaurs. Perhaps, he suggests, the world would be populated by descendants of the rodents, with rodent herbivores and predators and even a rodent intelligent life form.

As one would expect from Dawkins, The Ancestor's Tale is science popularization of high quality. What comes across most strongly is his sense of wonder at the fact of life itself. This is an excellent counter-argument to people who say, absurdly, that science and poetry are mutually incompatible. In a time when science seems to be becoming increasingly devalued in favour of irrationality and mysticism, that is something to be grateful for.

20 August 2005