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Sex under pressure

Nature volume 430, pages 613614 (05 August 2004) | Download Citation


If sex is so important for evolution, why don't we have more of it?

Why We Do It: Rethinking Sex and the Selfish Gene


 W. W. Norton: 2004. 224 pp. $24.950393050823

Life is for living: selection affects every aspect of our lives, so does it all come down to sex? Image: D. BRAGG/HTTP://WWW.EVERYNIGHT.CO.UK

I opened this book with considerable anxiety. The blurb and advance praise on the back make clear that Why We Do It (have sex, that is) aims to shatter myths, recast darwinism and fundamentally change the way we understand our own evolution. Niles Eldredge, an invertebrate palaeontologist and one of the major figures in the macroevolutionary debates of the 1970s and 1980s, sets out to tear down the whole edifice of reproduction-driven neodarwinian behavioural and evolutionary ecology. If Eldredge's explicit idea is correct, then anyone reading this book should emerge completely purged of the orthodox model of evolution as a process of enhancing reproductive success. No wonder I was anxious.

Eldredge's argument is straightforward. Sex for most animals, including or even especially humans, does not happen very often. Most of life is filled with growing up, finding enough to eat and avoiding predators. Sex is only occasionally interspersed among these activities — I leave it to other readers to quantify this, as I suspect there must be considerable variation. Indeed, this is one of Eldredge's main points: there are some individuals — and we're talking about humans here — who never have sex. What follows from this, Eldredge argues, is that because sex is relatively rare, it must, in evolutionary terms, be relatively unimportant.

The next step in the argument is that sex is the source of the ‘selfish gene’ or ‘gene-centred’ model of evolution, so this model clearly must be wrong. Selection is not for sexual and reproductive success alone, but affects all the other events between birth and death. As Eldredge says, life is for living, not for having sex and reproducing, so fitness for life — not for the ability to spread genes — is what the game is all about.

Eldredge then sets out to establish that there are, within the arena of evolution, two separate spheres: reproduction and economics (drawing on some of Darwin's original formulations). Selection operates on both of these independently and, if anything, selection for economic factors is more important than selection for reproductive success, on the grounds that more effort goes into it. From this point comes a battery of assaults on the role of evolution in human behaviour: the dismissal of evolutionary psychology, the dominance of culture over biology, the separation of sex from reproduction in humans (reducing even more the significance of reproductive success), and an attack on biological determinism in human affairs.

At heart, the book is deeply anti-gene. It argues that genes are wrongly placed at the centre of evolutionary theory, that genes do not play an active role in the evolutionary process, that genes do not greatly influence human behaviour, and that the genetic heritage of human evolution is not significant.

Is this the end for those Eldredge portrays as the ultradarwinists — notably Richard Dawkins, E. O. Wilson, all evolutionary psychologists and probably most behavioural ecologists? Has Eldredge demolished gene-centred evolutionary theory? Hardly. The logical error in Eldredge's argument is so breathtakingly obvious that one can only wonder how he has missed it. Reproductive success is not just about having sex. Take virtually any animal, and certainly it may spend relatively little time actually copulating, but what Eldredge isolates as the economic sphere is clearly not independent of sex and reproduction. How an organism grows — with males of many species being larger than females, for example — is not an isolated biological phenomenon, but represents an individual (through its genes) positioning itself to compete well in the reproductive arena. Its social behaviour, being competitive or cooperative, and its feeding ecology are all part of its reproductive strategy — and hence are selected not just for their own efficiency, but for the extent to which they contribute to reproductive success. Countless studies across vast numbers of species have shown how patterns of ‘economic’ behaviour are related to reproductive strategies and success.

Humans are the central concern for Eldredge. It is to his credit that his primary argument is not that selfish-gene models do not apply to humans because they are different, but that selfish-gene models do not work for any organisms, and therefore apply even less to humans. Ultimately, as the final chapters make clear, this book sees in classic neodarwinism the dangers of biological determinism, and views evolutionary psychology in particular as the modern version of the older threats of social darwinism and eugenics. There is plenty on humans here, but whether this has much to contribute to debates on the relative roles of genes and the environment in human behaviour, and on whether human behaviour is shaped by strategic concerns over reproductive fitness, is a matter of doubt. The evidence on human behaviour takes the form of anecdotes about how we do not have as much sex as we could, or how we sometimes behave in ways that do not obviously seem to enhance our fitness. Although such anecdotes are indeed abundant, they hardly constitute serious scientific study.

It may seem harsh to criticize so heavily a book written in such an extraordinarily popular and friendly manner — this is not a scientific monograph, after all. However, the claims made here are so strong, so polemical and so tilted towards making reproductive fitness seem like an irrelevance in the evolutionary process that it would be inappropriate not to point out the extent to which a naive reader might be misled. There are many oversimplifications and difficulties with the strongly adaptive models of human evolution constructed by evolutionary psychologists and behavioural ecologists, but Eldredge's approach is too extreme to bring these out in any way that might usefully influence future developments.

Should you read this book? It is written in a chatty and homely style, which will appeal to some and grate on others. Even the notes provide little bibliographic support for the points made in the body of the book, being rather an extension of the polemic by other means. If you are in the mood for some relentless Dawkins-bashing, or want a rush of arguments against biological determinism, then you might enjoy it. But if you are a neodarwinian in search of a road-to-Damascus experience, this is not the place to find it. And if you are a neodarwinian not looking for such an experience, you had better avoid this book, as its superficiality, inconsistency and misleading logic will only irritate. On the other hand, you need not have any fear of having your evolutionary world turned upside-down. I closed the book with a sigh of relief.

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  1. Robert Foley is in the Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Downing Street, Cambridge CB2 3DZ, UK.

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