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SEXUAL climax for the male is, evolutionarily speaking, rather dull. Its raison d’être seems crystal clear. Orgasm fosters men’s reproductive success, because it is linked to the ejaculation of sperm. Only devotees of tantric yoga, apparently, can achieve orgasm without ejaculation.

But women too are able to experience orgasm. Sexologists have documented the “clonic contraction of pelvic and abdominal muscles initiated by a spinal reflex”, and, in Elisabeth Lloyd’s favourite definition, the “combination of waves of a very pleasurable sensation and mounting of tensions, culminating in a fantastic sensation and release of tension”. What has puzzled generations of thinkers, however, is why women, as well as men, should have evolved the capacity for such sexual pleasure.

Over the past century, scores of biologists have sought an answer in natural selection. In The Case of the Female Orgasm, Lloyd, who is a professor of biology at Indiana University, has totted up 21 alternative explanations. All these “adaptationist” theories share one thing: the belief that women have evolved the capacity for orgasm because it fosters their reproductive success. In one of the most popular accounts, female orgasm is the cement in pair bonds: mutual pleasure fosters happy monogamous couples who share childcare ever after. The latest idea, “sperm competition”, is more hydraulic in tone. It argues that orgasmic contractions of the uterus are designed to suck up sperm from the vagina, fostering the reproductive success of the male who gives pleasure to his partner.

There is one big problem with all these ideas: no study has ever established a reliable link between a woman’s orgasmic capabilities and her fertility or fecundity. And that, says Lloyd, should immediately set warning lights flashing.

And there’s another problem: the glib assumption that female orgasm is designed to happen during heterosexual intercourse. In fact, the data shows that many women struggle to climax during conventional penetrative sex, and usually do so only with direct clitoral stimulation. Yet during masturbation both women and men can achieve orgasm in about four minutes.

The conclusion, Lloyd argues, must surely be that the female orgasm has no biological function. Rather, it’s on a par with the male nipple – an accident of shared developmental pathways in the early embryo. Because women need nipples to suckle their babies, men end up with rudimentary versions too. They may not give milk, but like the female’s they have erotic sensibilities.

As for genitalia, because men need ejaculatory penises, women end up with clitorises capable of similar sexual pleasures. Lloyd reckons that biases in evolutionary thinking have blinkered generations of mostly male biologists. It is time to give up the adaptationist’s fallacy and face facts. The late Stephen Jay Gould, who encouraged Lloyd’s long-standing investigation, must be cheering from above.