Sharp exchange over the blunt scythe of selection

Evolutionary psychology has created bitter divisions. The only way forward, writes Tom Sambrook, is through balance and dialogue.

Freud and Marx are dead: Long live Darwin, observes Barbara Hernstein ironically in Alas, Poor Darwin . Evolutionary psychology's (EP) strident claim to the humanities receives here the attention of a formidable band of eminent biologists and philosophers. For a young discipline, EP has certainly upset a lot of people.

Its claims are familiar enough. The brain is a costly organ that can only have been selected if it is adaptive. Since modern humans emerged in the Pleistocene, our brains are adapted to the problems faced by a Stone Age hunter-gatherer. A 20th-century commuter-gardener merely adapts these inherited modes of thought to their latest environment. For cave selection read feng shui , for mammoth hunting read golf.

Here is what Alas, Poor Darwin has to say. EP has a naive view of genes as abstracted naked replicators ( viz Richard Dawkins's selfish genes). EP has a naive view of evolution. Natural selection is not the sole engine of evolution and it is certainly not "algorithmic" because the different substrates (gene, individual etc) on which it acts behave differently. EP has a naive view of the brain, looking for static architecture where there exists dynamic function. EP's practitioners do not know much about the brain and so, for example, Steven Pinker's computational account of cognition is purely metaphorical until such computations are observed. EP has a naive view of thought: the atomistic philosophy of natural science is not applicable to the humanities (viz Dawkins's selfish memes). EP has a naive view of people: indigenous societies whose ethnographies fitted EP speculations two decades ago have mostly changed, in flagrant disregard for their Pleistocene genome. EP posits unknowable selection pressures because we do not know what problems humans faced in the Pleistocene. If we construct the past using the present - the Flintstones approach - EP becomes circular. EP is naive science. A class of Anglo-American scientists have mistaken their simplifications for simplicity in their subject matter and go chasing solutions (adaptations) to problems created by their own theory (adaptationism). EP is dangerous, for it passes culpability from individuals to human nature and, ultimately, natural selection. It is motivated by the religious desire to explain the meaning of life through a cosmic principle.

Alas, Poor Darwin , as its subtitle reveals, is a polemical work and uses polemical devices. The argument ad hominem that EP practitioners are religiously motivated is an example. Thinking hard about universal principles is necessarily religious. Newton's (correct) discoveries were religiously inspired. Postmodernism (the tenor of this book), which urges detachment from universal theory, is rather the exception. Tut-tutting scientists for "moving from questions of how, to questions of why" is a red herring: for any self respecting scientist the two are the same. EP theorists do posit a universal principle of selection but it is not a "telos", because natural selection, famously, does not have a purpose. This makes it uniquely resistant to hijack by political ideology.

There is, inevitably, an ideological streak running through this book. Hilary Rose argues that "democratic societies assume that our institutions work better if they reflect the diversity of the population they serve". Here is the nub of it: science is indeed an institution, mostly conducted by a privileged group. But are we then to have pluralism as our aim in a scientific account of behaviour? If so, why stop with human psychology. Let Pakistanis have a different value of pi from West Indians. Investigate whether light travels faster for men than women. The quandary of scientists as humans seems insoluble.

The other motive that drives EP's detractors is aesthetic. It is the origin of the wrangles between Stephen Jay Gould and the Daniel Dennett-Richard Dawkins camp and it concerns what makes a satisfying explanation. For the former and his fellow contributors to Alas, Poor Darwin , that which satisfies is multiplicity, mystery and unpredictability.For the latter and their EP colleagues, it is the compression of comp-lexity into simplicity.

I do not think this book is fair on EP or seeks any kind of useful dialogue, but I am glad it has been written and hope EP theorists will take the better charges seriously. Balance is the foremost requirement of a society trying to juggle the true, the beautiful and the responsible.

Having chided the Roses for unfairly caricaturing EP, A Natural History of Rape - described by them as "the nadir of EP's speculative fantasies" - makes rather depressing reading. Its authors argue that rape evolved in males for its reproductive benefits because it allows them to circumvent female choice. It behoves us to accept this since "rape could cease to exist only in a society knowledgeable about its evolutionary causes". The authors start with Randy Thornhill's interesting work on forced matings in scorpion flies. Through ingenious experimentation he has shown that the male scorpion fly's "notal organ" is used only for forced matings and, as such, it is reasonable to suppose that the organ has evolved for that purpose. A Natural History of Rape comprises a search for some equivalent of the notal organ in the human male psyche.

The evidence is not compelling. The fact that many rapes are committed by men without the financial resources to attract a long-term mate is hopelessly confounded by other social factors. The authors' studies of ejaculate composition from masturbation in response to videos of rape are ecologically invalid. The evidence on which they hang their argument and to which they contin-ually return is that young and therefore fertile women are the most common victims of rape. The jaw-droppingly obvious point here is that these women are more often found in situations where rape occurs and are more often in the company of the young men who are committing the majority of rapes. This fact is not mentioned once.

The authors fail as scientists because they do not look for evidence that would falsify their claims. A decent cross-cultural analysis would simultaneously test for universality and illuminate the role of cultural mediation. Its absence makes it difficult for the authors to bridle at being dubbed genetic determinists. The rape of men is not considered. If their reaction were similar to women's this would disprove the notion that rape-induced psychological trauma has an evolutionary origin in lost mate choice (men do not conceive). If it's all down to sexual attraction, why was it despised Chinese women who were raped by Indonesian men in the Jakarta riots? What about non-copulatory rape? What about child molestation?

Thornhill and Palmer argue that, because Homo sapiens evolved, it is necessarily true that all human behaviour evolved. Yet while this semantic nicety assures rape's status as an "evolved behaviour", it does so equally for credit-card fraud and littering. Thornhill and Palmer do distinguish between evolved adaptations and "by-products" - but then subsequently ignore the distinction.

The authors are particularly disparaging of the ideology of the "social science argument" that rape is motivated by the desire to control, rather than sex per se. They have a point when they say that this theory has served an ideological purpose; still, if that was its only buttress, then Thornhill and Palmer ought easily to be able to knock it down. Yet they do not address the control theory at the proximate level at all. This is the worst sort of EP, that writes off non-evolutionary explanations as literally impossible.

Rape as an evolved reproductive strategy is not a bad hypothesis, and certainly it is likely that evolved sex differences feed into the rape equation. But sandwiched between the authors' enthusiastic championship of EP and their declamations against social science lies remarkably little substance even for EP sympathisers to chew on.

Dear Mr Darwin cannot at least be accused of simplifying matters. Recalling my conversion as an adolescent to the simplicity of Richard Dawkins's grand vision in The Selfish Gene , my reaction to Gabriel Dover's book was "damn, now it's got all messy again". The problem, ironically, is with the genes. To Theodosius Dobzhansky's famous observation that "nothing in biology makes sense except in the light of evolution", Dover adds that nothing much in evolution makes sense except in the light of genes.

Genes, it seems, are not as well behaved as Mendel's pea plants led us to suppose, and Darwinists have been guilty of neglecting this fact. Their unruly behaviour, dubbed by Dover as "molecular drive", includes an ability to proliferate and relocate within the genome and to bias the production of sex cells towards holding one version of a gene rather than another. Since evolution has traditionally been regarded as changes in gene frequency over time, biased sex-cell production considerably undermines natural selection's status as evolution's prime engine. Internal selection of sperm and ova carrying A (dominant) rather than a (recessive) will drive gene frequencies much more effectively than the blunt scythe of natural selection.

A further fallacy, and one that Dover lies squarely at the door of Dawkins, is to regard genes as units of selection. Most functions of an organism are regulated by more than one gene and most genes contribute to more than one function. As such, selection can at best act on gene clusters.

Dover draws out some interesting implications of the new genetics for evolution. Concerted proliferation of neutral changes in a population's genome can speed up speciation (no need for niche segregation). Molecular drive makes evolution easier since initially harmful mutations that in the future can be co-opted into new traits can be internally buffered by molecular co-evolution. The modular approach to gene expression also tackles the thorniest problem that Darwin's insistence on gradualistic evolution encountered: how new adaptations can arise when their early stages are maladaptive (eg half a wing).

In principle, molecular drive could upset our entire view of evolution. In practice, we need to know a lot more. The value of natural selection as an explanation of life is that it is clearly directional for a given trait.There might be directionality in molecular drive originating from exciting genetic laws yet to be discovered. Alternatively, molecular drive might be a powerful but random force, in which case, like meteorite impacts, its explanatory power is historical rather than predictive. So, granted it is messy, but what sort of mess are we in?

In The Mating Mind , Geoffrey Miller, a rogue element in the ranks of EP, ponders the role of sexual selection in the evolution of the human mind. While Darwin's favourite theory scandalised Victorian scholars and layfolk alike, a glance at today's magazine racks reveals that now the zeitgeist is unquestionably more favourable.

Sexual selection explains non-adaptive traits like the peacock's tail as an evolutionary response to preference by potential mates. The preference may be based in the advantage of producing "sexy sons" or because the self-handicap imposed by the trait indicates otherwise good genes in its owner. Miller argues that the human mind is a kind of peacock's tail. It is costly and, because it is complex, it is an accurate representation of genetic quality. Furthermore, if brain complexity was a useful trait for early humans, then displays of its generative capacity would be honest indicators of fitness. The mind then, is a courting device designed to stimulate and be stimulated.

Under Miller's exposition, the hand of sexual selection in the human mind is apparent everywhere. Speech, a problematic faculty in evolutionary terms which at first sight seems to benefit the listener more than the speaker, was selected for flaunting mental peacockery. Our capacity for an extended vocabulary (a trait that is partly heritable) vastly exceeds the requirements of dealing with nature: courtship is its application. Altruism, in all its guises, is a form of conspicuous self-handicapping. Indeed, Miller observes that the most romantic acts are those that bring little benefit to the receiver but great cost to the giver. Stone Age woman as traditionally viewed, choosing men with resources, would have been left distinctly nonplussed by a priceless but inedible orchid.

Note that only male peacocks have the fantastic tail since females are the choosers. The equally developed female and male brain in humans therefore speaks for generations of mutual mate choice in contrast to EP's traditional assumption of female choice.

This delightful scenario of Cyranos and Scheherazades contains more theoretical ballast than I can outline here. There remains, nevertheless, a large gap between theory and anecdote in which data would normally lie. I would like to have seen at least an outline of how the theory will be tested. Sexual selection's explanatory power is also its weakness, for since beauty is in the eye of the (ancestor's) beholder, it can be used to explain away any apparently unnecessary trait, relieving us of the chore of looking for alternative explanations.

Still, an explanation is yet demanded of the ape Homo sapiens and its curiously self-constructed environment of extended foreplay, lightning wit and virtuoso jazz: an explanation so far unforthcoming from the two monoliths of Gene and Culture. Compared with the gloomy censures of EP's detractors and the shiny promises of a reduced-in-the-pan account of me and my genes that I am not sure I want to hear, Miller's tale is licentiously playful. Speaking merely as a human being and the singular product of five million years of evolution, the pleasure of reading The Mating Mind is what makes me wonder if there is something in it.

Tom Sambrook is a teaching fellow in psychology, University of Stirling.