For the first time, scientists have been able to tease out the role that genes may play in determining how easy it is for a woman to reach a climax during sex. Researchers found that the ability to achieve orgasm varies widely between women and that between 34 and 45 per cent of this variation is due to genetics rather than other factors, such as culture, upbringing or religious beliefs.

Professor Tim Spector of St. Thomas' Hospital in London, who led the research, said the findings may help to explain why one in three women says she achieves orgasm either rarely or not at all with her partner.

Biological Underlying Influence

"There are women who find it very easy to achieve orgasm and there are those who don't," Professor Spector said. "What these results show is that as well as this wide variation, there is clear evidence of a biological underlying influence here that we can't purely attribute to culture, upbringing, religion or race. There is something biological that's determining some of this large variation between women and if something is heritable it is unlikely to be by chance."

Previous surveys of sexual behaviour have shown that women are far less likely to have an orgasm than men during sex and that they take longer to reach a climax when they do have an orgasm.

The latest study, published today in the journal Biology Letters, interviewed more than 4,000 women, all of whom were either identical or non- identical twins, a factor that allowed the scientists to compare the role of genes and upbringing in influencing orgasm.

Professor Spector said the investigation was done as part of a large study of twins which investigates the role genes play in a wide variety of traits, from ailments such as hypertension and migraine to musical ability. Inability to achieve orgasm should be treated like other forms of sexual dysfunction that are treated more seriously by the medical profession, he said.

"There is so little research done on female orgasm. It's like a taboo subject. For some reason it's treated very differently to male impotence. Female orgasm is regarded by some people as a made-up problem. Sexual dysfunction as it is euphemistically called, is [said to be] made up by the drug companies or medical institutions."

Selecting a Mate

The interviewees in the study, whose ages ranged from 19 to 83, were more likely to achieve orgasm on their own than during intercourse, with just one in five saying that they never or infrequently had an orgasm during masturbation. Professor Spector said that 34 percent of the variation in ability to orgasm during intercourse was due to genes while 45 percent of the variation during masturbation was due to genes.

"The masturbation figure of 45 percent is in the same range as [the role of genes in] hypertension or blood pressure. It's in the same range as migraine, depression, and timing of the age of menopause," he said.

"It was all done anonymously and in that way we believed we were getting honest answers. The important finding is that there is huge variation in the reporting in the ease of achieving orgasm with really a massive range. One in three women reported never or infrequently achieving orgasm during intercourse and as many as 21 percent during masturbation."

Although the male orgasm plays a vital biological function in reproduction, the role of the female orgasm is less obvious. It may increase the ability of a woman to achieve fertilization of her eggs during the most fertile period of her menstrual cycle.

Another theory is that it plays a role in selecting a mate, Professor Spector said. "Because of the disparity in time of reaching an orgasm between men and women, it's a way for women to assess men in their sexual powers or ability, which in a way is a marker for whether they are likely to be a long-term mate."