THE quality of a woman’s sex life depends largely on her genes, according to research that shows that her ability to have orgasms is as heritable as her blood pressure.

The varying ease with which women reach sexual climax is more heavily influenced by genetic factors than any other, British scientists have found. Inheritance outstrips the contributions made by upbringing, culture or male bedroom skills.

The study of almost 1,400 pairs of female twins revealed that genes affect arousal at least as strongly as they do medical conditions in which their role has long been established, such as hypertension, migraine and depression.

It also suggests that the elusiveness of the female orgasm is evolved, probably because it confers a reproductive advantage that is triggered only with a particularly desirable partner.

Two theories have been advanced to explain this. A climax could make conception more likely when women have sex with an attentive, high-quality mate by flushing sperm higher into the reproductive tract. Alternatively, female orgasms could strengthen pair-bonding, so that any resulting children have the benefit of two parents instead of one.

Either way, orgasm would not work as a mate-selection tool if it could be achieved too easily. It seems instead to rely on subtle physical and psychological clues that mark out men as good father material and discriminates against the reproductive chances of mates who lack them.

“The theory goes that if a man is considered powerful enough, strong enough or thoughtful enough, in bed or in the cave, then he’s likely to hang around as a long-term partner and be a better bet for bringing up children,” Professor Tim Spector, of St Thomas’ Hospital in London, who led the research, said.

“Women who orgasm too easily might be less good at selecting partners.”

The study, which is published today in the journal Biology Letters, sought to establish the extent to which genes and the environment contribute to the female orgasm, by comparing 683 sets of identical twins with 714 sets of non-identical twins. Such studies are one of the chief tools available to scientists seeking to tease out the role of inheritance in human biology and behaviour.

While identical twins share all their DNA and a childhood environment, non-identical twins share an environment but only 50 per cent of their genes. If a trait is more commonly shared by identical than fraternal twins, it probably has a big genetic component.

The participants completed a detailed survey about their sexual histories. They found that while 14 per cent of the women studied had an orgasm every time they had sex, 16 per cent had never reached a climax this way and another 16 per cent seldom did.

Genes were responsible for 34 per cent of this variation, the comparison between identical and non-identical twins revealed, indicating that inheritance is the single most important factor in women’s capacity to orgasm. Though the influence of environment as a whole is greater, no individual element of nurture, such as religious or family background, accounts for more than a few per cent of the differences.

The genetic effect was stronger for masturbation, which allowed 34 per cent of women to reach orgasm every time, with 14 per cent failing ever to achieve a climax. Inheritance accounted for 45 per cent of this variation, reflecting in part the removal of a key variable, the lover’s sexual prowess.

“What these results show, as well as wide variation, is clear evidence that biology is an underlying influence here,” Professor Spector said.

“You can’t attribute the differences purely to culture, family upbringing, religion and race.These figures are in the same range as hypertension, which is 45 per cent heritable, and also migraine, depression, and the timing of menopause,” he said.

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