Roses are red, violets are blue. So what?

Valentine's Day comes at a time when a rash of new Darwinist thinkers are claiming that love is controlled by evolution. Do we have to listen? Of course not.

Talking to an ageing Don Juan the other day, I was struck by his sudden defence of his behaviour. "It's in our genes," he said comfortably. "I could impregnate every woman in this room, but you couldn't have a child with every man in this room. So men evolved to be really, really promiscuous."

"And doesn't that make you feel good," I said.

"Sure," he said happily.

In the 19th century, that same man might have believed that God made men to be leaders and women to be followers. In the early 20th century, he might have believed that his unresolved Oedipus complex led him to make a pass at any woman within range. Now he believes that he is the product of his genes. Evolutionary psychology is replacing religion and psychoanalysis as the theory people fall back on when they want to argue that women and men are different, and why that will never change. There is nothing new about the patterns that evolutionary psychology purports to see in male and female behaviour. Men are promiscuous, women are coy. Men argue, women gossip. Men like battles, women like babies. Men like pretty women, women like powerful men.

You don't have to look far, these days, to find evolutionary explanations posited for every nuance of our personalities. Geoffrey Miller, senior research fellow in evolutionary psychology at University College London, has argued that men go into politics as a way of impressing future mates, because politics is the human version of the peacock's tail - pointless but sexy. Has Miller ever experienced the gloom and greyness of a party conference? Kingsley Browne, professor at Wayne State University, Michigan, argues that the reason that fewer men than women tend to put on a seat belt when they get into a car is that risk-taking gives men a reproductive advantage by getting them more resources - and the poor human monkeys have forgotten how to distinguish between risks that get the bananas from under another monkey's nose, and risks that bring no benefit at all. A book published last week, Why Men Don't Listen and Women Can't Read Maps, by Allan and Barbara Pease, explains why men can't find missing socks and butter in terms of million-year-old propensities. "As traditional nest defenders, women have developed brain software that gives them a broad spectrum of vision. In contrast, as hunters men have evolved a type of long distance 'tunnel vision'." And so, apparently, men can look in a fridge and not see the butter in it. Give the chimp a break, and stop asking him to do the housework.

This new fashion for evolutionary psychology has spread with bewildering speed. It was only in the mid-Seventies that Darwinism was taken up and dusted down and began to be examined again for its implications for human behaviour. Now, evolution is booming. Last Wednesday, you could have caught Steven Pinker, author of How the Mind Works, and Richard Dawkins, author of The Selfish Gene, battling it out in Westminster before an audience of more than 2,000 people. On the very same night, Helena Cronin, author of The Ant and the Peacock, was giving a public lecture on evolution and sexual difference in Oxford. These evolutionary gurus are ubiquitous; they are invited to give their views everywhere from Start the Week to the Davos World Economic Forum; their books sell and sell. Some make extreme claims for the contemporary relevance of the theory. Steven Pinker wrote in the New Yorker recently that Clinton's behaviour was a typical product of male evolved propensities, since "most human drives have ancient Darwinian rationales". "The new Darwinian synthesis," wrote Robert Wright, author of The Moral Animal, in 1994, "is a body of scientific theory and fact, but it is also a way of seeing everyday life. Once truly grasped it can entirely alter one's perception of social reality."

It can indeed alter one's perception of social reality - but does it do so truthfully? When evolutionary theory is pressed not just into the service of explaining observed traits in ants and peacocks, but also into explaining modern human behaviour, how accurate is it? Evolutionary psychology has a lot to say on the differences between men and women - both Helena Cronin and Geoffrey Miller have books in preparation on the subject. Here the evolutionists rely on the theory of sex selection, that men and women have evolved to be different because men and women have always looked for different things in their mates. As Helena Cronin put it in Oxford, "Give a man 50 wives and he can have children galore. Give a woman 50 husbands - no use at all. Natural selection favoured men with an appetite for multiple mates, and favoured women who went for quality."

From this basic premise, that men have evolved to be more promiscuous than women, everything else flows. You can then argue that men have evolved to value youth and beauty in their mates - because looks, according to Cronin, are a good indicator of health and fertility. And conversely, you can argue that women have evolved to value resources, status and power in men. You can argue that men have evolved to be more competitive in their everyday behaviour, in order to gain more resources to attract more women. From all that it's but a short step to evolutionary explanations of political leadership, the use of seat belts, and who can find the butter.

The popularity of this sort of evolutionary psychology is not, of course, an isolated phenomenon. Throughout our culture we are currently seeing a new resurgence of a very old idea: boys will be boys, girls will be girls. The heady days of the Seventies, when I was denied a Barbie doll because my mother thought it was a sexist fantasy that would warp my tiny mind, seem to have passed into a new fatalism about male and female behaviour. There are hundreds of culprits. John Gray's self-help book Men Are from Mars, Women Are from Venus, tells couples to accept and work with their innate differences. Another best-selling self-help guide, The Rules, told women that if they wanted to snare a mate they had to exaggerate their coy behaviour. Men Behaving Badly smiles on women's doomed efforts to change their men and Bridget Jones goes right back to the idea that men are all bastards and women just want to get married. All these phenomena are devoted to pressing home the idea that men and women are as different as different can be. And evolutionary psychology is providing a convenient scientific back-up for this cultural shift.

We need to think at least twice about a theory that is gaining so much ground so quickly, all the way from Oxford University to the Mail on Sunday. Just as women - and men - are beginning to feel that they might be able to throw off the constraints of ages, is evolutionary theory threatening to put us back in pink and blue boxes? When it is explicitly used, as it was in the television series Why Men Don't Iron, to back up the view that men shouldn't be asked to do domestic work; or in Kingsley Browne's book Divided Labours, an evolutionary view of women at work to pour scorn on the idea that women will ever take power in the workplace, we should be aware that new gains are being threatened. And when women in the West are at last beginning to feel that they can throw off the old constraints, it is sobering to realise how many scientists are pushing us to accept that, say, "women do not seek the sight of naked male strangers" as an unchanging truth. Has Steven Pinker ever been to a hen night?

Helena Cronin is one of the few people working in evolutionary psychology who would call herself a feminist. She argues that evolutionary psychology need not be deployed for conservative ends. Her view is that even if men have evolved to be more promiscuous and competitive, that doesn't mean that their behaviour is better or that it should, any more, be the model. She believes that much of that competitive showiness is merely wasteful. "Modern Darwinian study would reveal much of the modern workplace to be an arena for prodigious male display, jostling to be up front and make a splash, busy, risky, but to no very productive end."

That argument has its own integrity; but we can challenge the conclusions of evolutionary psychology on a much deeper level than that. It always relies on double statements: men are naturally like this now, it says; it suited men in the Stone Age to be like that. But when both sides of a statement are shaky, the argument cracks. When it comes to generalisations on contemporary behaviour, can we be sure that, in the surveys on which the evolutionists rely, people are responding according to their natural and innate drives or merely voicing what they feel is socially acceptable? What is the evidence, for instance, for the statement that women have "evolved" to look for power in their mates, while men have "evolved" to look for youth and beauty? Certainly, a "cross-cultural" survey undertaken by an older powerful man has found that women do like sex with older, powerful men. But women are still locked out of society's resources unless they have the security of a powerful mate; so our evolved propensity may not be towards fancying older men, but towards flattering them if it profits us. If society changes to allow women more power of their own, our sexual drives may find freer expression.

Again, a survey published just last week showed that British women are now saying they would like to have younger men as their sex partners. And the only study undertaken on what women find attractive in male faces found, directly contrary to the predictions of the evolutionists, that women went for highly feminised, pretty, youthful male faces - the Leonardo DiCaprio end of the scale.

Similarly, what real scientific validity is there in the stories that evolutionary psychologists tell us about how our ancestors behaved on the Pleistocene plains? We will never find the fossils of the million- year-old lonely hearts columns, and too many of the tales that evolutionary psychologists tell sound like dreamy justifications of our present society rather than anything that might have taken place millions of years ago. Evolution has no doubt moulded our brains and desires, but we cannot define exactly how, or why. Natalie Angier, in her new book Woman (published in March by Virago), points out that the only thing we can be sure of is that our ancestral environment selected a huge variation in the possible mating strategies of individual men and women. As Barbara Smuts, author of Sex and Friendship in Baboons, says, "Flexibility itself is the adaptation." Who knows, male monogamy and female promiscuity may even have been the norm millions of years ago, and either choice is - again - available now. Female competitiveness, female power, male parenting skills, male gossip - there is no evidence that these traits have been bred out of us, just that our current society does not favour them. The simpler truisms of biology may turn out to be merely a block on our individual potential.

And if we stare too long at these surveys and "explanations", we run the risk of reducing the passions and pleasures of romantic love to the dullest game in the book. "Emotions are just evolution's executioners," says Robert Wright. So why do they keep flouting the rules? Think of the murmurs of the monogamous male - take Birkin in Women in Love, with his assertion that "There remains only this perfect union with a woman - an ultimate marriage - there isn't anything else"; think of the glorious cries of the promiscuous female, such as Anais Nin. Think of a woman like Jane Eyre, who could love her Rochester only once she had gained her inheritance and he had lost his power, once he was actually blind. Think of Antony, who loved the fierce and quick-witted Cleopatra far more than the boringly modest Octavia. Think of Anna Karenin, who gave up her stable, powerful husband for the young loser, Vronsky. Think of any love that actually makes your heart beat faster, and you realise it isn't going to be the typical mating game of the evolutionary psychologists, because, thankfully, life is so much more complicated and interesting than that.