Uncharacteristically for the discipline, biology classes of the future may be interested in a particular historical date. This date will have more fundamental importance than the Battle of Hastings or the Roman Conquest. It is the date (give or take a decade or two) at which humans stopped evolving. It is an unnerving thought. Is that date fast approaching? Has it already passed? Christopher Wills argues that, on the contrary, human evolution is fast accelerating.
Children of Prometheus conveniently breaks down into a study of the past, the recent past, the present and the future. Wills demonstrates that humans have evolved faster than chimpanzees in the 6 million years since our lineages split, which is un-startling. Nevertheless, it is refreshing to hear a genetic explanation rather than the usual speculations about prehistoric selection pressures. In this case Wills draws attention to microsatellite or "junk" DNA, which, while failing to code for any useful protein, increases mutation rates and therefore evolutionary potential.
Wills further argues that human habitat modification in the 10,000 years since the beginning of agriculture has resulted in a host of new selection pressures (the increased incidence of malaria being a powerful example) and has accelerated evolution as a result. This contrasts with evolutionary psychology's assumption that humans are, evolutionarily, still designed for a hunter-gatherer lifestyle.
What of the present and the future? Eugenicist fears that cultural suspension of "natural" selection (eg via welfare) would degrade the human stock are not borne out: IQ is steadily climbing in the western world. The lifting of nutritional and disease constraints on children is starting to reveal their true genetic potential. Wills argues that many aspects of the human phenotype will change greatly in the next few decades as a result of human induced environmental changes.
Still, this is not evolution proper - such as changes in gene frequency. Our increased ability to control development and the expression of genes will ultimately remove selection pressure exerted on them. Indeed, Wills has the nub of it when he predicts that in the future we will "move from the realm of what we must do to that which we can do". The most obvious example of this is the choice not to have children, a very recent phenomenon in the West resulting from contraception, women's emancipation and changing aesthetic ideals. But for Wills's claim of accelerating evolution to stand up, he really ought to have discussed human reproduction because that is where selection occurs.
In sum, what has happened recently in human evolution is not a guide to what will happen. This makes for a rather obvious join in Wills's argument. We simply do not know what humans will be doing in the future. The moratorium on genetic engineering of human sperm and ova will doubtless not last forever: once couples have won the right to bear children free of the genetic disease of cystic fibrosis, the genetic "diseases" of obesity and ugliness may not be far behind.
Wills is sanguine about the prospect of humans reaching their "full potential". Our full potential will depend on the criteria of the future, and on the criteria of those with access to genetic technology, though I agree with Wills that these will become ever more diverse. But whether humans will become the first species on the planet to be self-selecting or whether their hubris will suffer natural selection's cool judgement remains at present the subject of science fiction.
Thomas Sambrook is a teaching fellow in psychology, University of Stirling.
Children of Prometheus: The Accelerating Pace of Human Evolution
Author - Christopher Wills
ISBN - 0 713 99348 0
Publisher - Allen Lane The Penguin Press
Price - £20.00
Pages - 310