Twins shed light on female orgasm

The ability of a woman to have orgasms during sex is partly influenced by her genetic make-up, say UK researchers. A study of twins, published in the Royal Society journal Biology Letters, estimates that an inability to achieve orgasm during masturbation is even more strongly controlled by genes. The team, based at St Thomas' hospital in London, suggest that reaching an orgasm could help women assess the suitability of a man as a long term partner.

The researchers studied 4037 adult twin women, aged between 19 and 83. Scientists have studied twins for many years, in order to measure the influence of genes and environment on a wide range of traits. They compare identical twins, who have identical genes and similar backgrounds, with non-identical twins - who also share similar backgrounds, but are no more genetically alike than ordinary siblings. In this way, researchers can estimate how much of the variation seen for a particular characteristic is accounted for by genes - a measure of heritability.

The St Thomas' team surveyed the women about sexual problems, and found that overall, 32 per cent reported 'never' or 'infrequently' achieving orgasm during sexual intercourse, while 21 per cent reported they did not achieve orgasms during masturbation. There was no difference between the identical and non-identical twins for this category. However, for women who did achieve orgasm, the frequency of orgasms was more likely to be the same for pairs of identical twins than it was for non-identical twins.

The researchers estimated that the ability to achieve orgasm during sex is 34 per cent heritable, while during masturbation it is 45 per cent heritable. Team leader Tim Spector says the study shows that there is an underlying biological basis to a woman's ability to achieve orgasm, which could be anatomical, physiological or psychological. He suggests that such a trait could have been selected during human evolution: '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', he said.

However, experts disagree over the evolutionary reasons for the female orgasm, with one theory suggesting that it increases sperm uptake, and thus fertility. Even if the findings of the latest study are confirmed, it does not necessarily mean that any of the genes involved will be identified - there are likely to be many genetic and non-genetic influences on such a trait. But Spector says more research into the subject could lead to new drugs to treat female sexual dysfunction.