Resemblance of things past

Nowadays whenever we are puzzled by some aspect of human behaviour (and often when we are not), some pundit pops up to tell us that it evolved to meet the needs of our hunter-gatherer ancestors. They flourished about 200,000 years ago, since when there has been insufficient time for radical changes in our genes. The means by which our ancestral genes spread themselves are not always appropriate for the present day: after all even the wisest hunter-gatherer gene could hardly have foreseen the advent of contraception.

Until recently almost all social scientists thought the environment was all important, a belief now held only by a handful of card-carrying communists and their allies. The vastly increased role allocated to genetics has two aspects. First, it is now apparent that many differences between individuals are largely innate. Genes are mainly responsible not merely for schizophrenia but for obsessive-compulsive disorder and many other forms of mental illness. They are also major factors in determining intelligence and personality.

Steven Pinker deals mainly with the second facet - the ascription of similarities in people's behaviour to nature, rather than to nurture. Within psychology this revolution in thinking was first stressed in The Adapted Mind, a book edited by Leda Cosmides and others, to which Pinker is much indebted. Its most original claim is that we can test experimentally predictions about contemporary behaviour that are derived from the habits of the hunter-gatherers. Pinker gives an example that blows up in his face. It concerns a problem that subjects find difficult to solve, but that has been shown to be readily solvable if it is couched in terms of detecting a cheat. Pace Pinker, this does not provide evidence for a cheater-detector gene (which no businessman, let alone a hunter-gatherer, should be without), as it has been shown that any formulation of the problem that emphasises the relevant material makes it easy to solve.

The new discipline of evolutionary psychology relies on our knowledge of hunter-gatherer societies partly gleaned from the study of contemporary tribes and to a lesser extent from the study of animal behaviour, for if a habit co-varies across species with a variation in environment or in another habit, the two are likely to be connected. But Pinker takes the argument further. He alleges that knowing the function of a practice enables one to infer the mechanism that subserves the function, "reverse engineering" as he calls it. He never justifies this claim - knowing that language is for communication, could we infer that it will be made up of nouns, verbs, adjectives and so on?

In a nod to the feminists, Pinker notes that innate behaviour can sometimes be changed. Such changes are, however, usually slight: try reasoning with someone who is violently sexually jealous. Of more importance, it must be remembered that the way genes express themselves is influenced by culture: whereas, at least until recently, modern football supporters would merely boo a biased referee, the hunter-gatherers would have lynched him.

Two-thirds of How the Mind Works is devoted to a perfunctory account of cognitive psychology and vision, topics that seem out of place in a book claiming to show the importance of function, since the reason these systems exist is usually so obvious as to be banal (consider the function of vision).

Moreover, Pinker's account is skimped and he misleads the reader by not mentioning unsolved problems - despite all the recent advances in vision, we do not know how the brain detects that a cross is inside or outside a square. Nor does he make clear how selective his account is: for example, he does not mention dark adaptation - an ingenious device to facilitate vision over a vast range of light intensities, which fits nicely with its function. It is a lengthy process, perhaps because both now and in hunter-gatherer days, the sun took a long time to set. Light adaptation on the other hand is very fast: perhaps hunter-gatherers leapt from their beds soon after dawn. This off-the-cuff functional explanation may or may not be right, but it demonstrates how easy it is to produce such theories.

Because he believes that all mental processes must have a function, Pinker is unwilling to admit that people can be irrational. Out of the dozens of systematically irrational types of decision, he selects five and with tortuous and unconvincing reasoning attempts to make them appear rational. Consider, for example, "the gambler's fallacy", the belief that if an event turns up several times in succession, an alternative is more likely to occur next time (six heads in a row are likely to be followed by a tail). Pinker argues that "the concept of probability implies a (mistaken) belief in a stable world", forgetting that the world must be "stable", otherwise we could not exist. He goes on to defend the gambler's fallacy with a story about his father correctly predicting that the weather would change, thus himself committing the fallacy of generalising on the basis of a single instance. (In fact, almost the best way to predict the weather is to assume it will be the same tomorrow as it is today.) The standard explanation of the gambler's fallacy, to take the case of tossing a coin, is that people know there are likely to be roughly equal numbers of heads and tails in a long series of tosses and hence believe - wrongly - that if there has been an excess of one it will be compensated by more of the other. The rest of Pinker's arguments about irrationality are just as unconvincing.

Pinker and indeed evolutionary biology in general are at their best on the topic of sex. Women produce relatively large eggs, of which only one is available at a time and they carry the growing foetus for nearly nine months, while men produce millions of spermatozoa. Because of the investment of resources the woman makes in her children and because she can only have a limited number, she has more commitment to rearing and nurturing them than the father, who can never know for certain that her offspring are his own. It pays a man to inseminate as many women as possible since this will propagate his genes at little or no cost.

Such considerations explain many of the differences between the sexes. Men would like to have sex with many women, whereas women are more averse to casual liaisons, a finding Pinker supports by quoting the results of a questionnaire (for social psychologists the questionnaire is the final arbiter; everyday observations count for nothing). In fact, men do have more affairs than women, which is odd because for every man having an affair there must be a woman having one (discounting homosexuals). Men's roving eye also explains why they are more fascinated and aroused by pornography than are women. Women seek in a partner someone of high status who can look after them, whereas men are attracted by physical beauty and youth, signs of health and therefore an indication that the woman will bear healthy children. Men's jealousy focuses on the sexual act because they may find themselves bringing up someone else's child rather than their own, whereas women's jealousy is aroused by her partner devoting resources to a rival rather than to her. Perhaps wisely Pinker leaves homosexuality unexplained: it is at least partially genetically determined, but the usual explanation is thin: homosexuals stick around the camp (hence the adjectival use of the word?) and increase the frequency of their genes by aiding close kin.

It is not easy to explain the range of human emotions, though Pinker has a determined try. He argues that adapting to misfortune is useful. But what possible use is the gradual decrease in happiness that follows good fortune? Again, although some phobias - of worms, blood, heights, and so on - have or had obvious survival value, it is hard to see the benefit of social phobias such as fear of others. Pinker suggests that grief reminds people that they may have been responsible for the death of their nearest and dearest and hence should be more careful in future. He does not mention that the less someone grieves the faster they return to normal functioning. One of Pinker's faults is that he is unwilling to admit that our emotions are not perfectly calibrated to our historic past. They may have unfortunate side-effects. For example, he cannot explain the persistence of those genes that produce disadvantageous departures from the norm, including depression and schizophrenia.

His attempt to trace our aesthetic sense back to our distant ancestors is particularly feeble. He argues that flowers betray the presence of fruit and are therefore regarded as beautiful, but on this thesis, a cabbage should look more attractive than a rose and an antelope more beautiful than a lion.

I have perhaps laboured the book's shortcomings, but only because convincing as some of it is, the claims made for evolutionary psychology seem to be exaggerated. Hypotheses about the evolution of mental activities are easy to make, but hard to prove. In fact How the Mind Works is for the most part well written and well argued. It covers an exceptionally wide range of material and one wonders of Pinker "how one small head could carry all he knew". The problem is that he seems to have been converted to evolutionary psychology late in life and strives too hard to support it, at the expense of providing many lame arguments. Not that it is all bad: for example, he suggests ingeniously that people sign contracts less to bind someone else than to prevent relapse on their own part.

Unfortunately he exhibits an unremitting pursuit of popularity, larding his book with jokes and stories, usually banal, taken from others. Apart from their tedium, they have made an already lengthy book much longer than need be and they interrupt the train of thought. The use of such phrases as "Beats the heck out of me!" will make some readers recoil. Nor do his constant references to those curious authorities on evolution - Woody Allen and Stephen Jay Gould - do anything to further Pinker's argument, no matter how similar are the pair's thought processes.

I much admired Pinker's previous book, The Language Instinct, which explained a complex subject clearly and agreeably. At times there is a touch of mania in its successor - even its organisation is somewhat chaotic. Pinker repeatedly claims that evolutionary psychologists are scientists, whereas in fact their methods of reasoning are usually more akin to those of the historian. He would have done better to stick to the more plausible aspects of the subject, while warning that not all behaviour is functional: even evolution cannot always get things right, if only because it has a limited set of genes to work with and there may be no route from the present state to a desirable future state that does not lower evolutionary fitness in between. In short, the reader should not swallow this book hook, line and Pinker.

Stuart Sutherland is emeritus professor of experimental psychology, University of Sussex.