BioEd Online

A woman's genetic make-up accounts for at least a third of her ability to climax during sex, say researchers, and may even account for as much as 60%.

Further investigations into the genetic differences that influence orgasms in women could help produce drugs to treat female sexual dysfunction, they say.

Relatively little is known about the female orgasm, the peak of sexual excitement normally marked by vaginal contractions. "It's a taboo subject," explains Tim Spector, who directs the Twin Research Unit at St Thomas' Hospital, London, and co-authored the report.

Women do not need to climax in order to conceive and give birth, a fact that makes the evolutionary cause of their orgasm slightly mysterious. In contrast, men who cannot orgasm miss the chance to pass on their genes and fall victim to natural selection.

So what function does the female orgasm serve? As well as making women more interested in the activity of procreation, recent investigations have found the contractions it involves can bring sperm closer to the egg, increasing the chance of conception.

Evolutionary psychologists have also suggested that the female orgasm might help women to select caring partners: those who are particularly attentive in the bedroom may also be more supportive in other aspects of life.

Twin peaks

To find out which factors most affect a woman's ability to climax, Spector and his colleagues sent a questionnaire to more than 4,000 female twins to complete anonymously. Recipients included nearly 700 pairs of identical twins, who share the same DNA.

The researchers asked how often the women climaxed during sex. Only 14% of the women reported always achieving an orgasm. At the other end of the spectrum, 16% of them said they never reach orgasm or are unsure about whether they do or not.

As in other studies of twins, the scientists assume that twins share similar family environments. The overall difference between trends in identical twins and fraternal twins is thus attributed to genetic influences. The analysis suggests that genes explain at least 34% of the probability that a woman orgasms during sex. When it came to masturbation, this number climbed to 45%, the researchers report in Biology Letters¹.

This number could go even higher, they add, if one could account for other variables, such as the different techniques of the women's partners. Genetic influences have been seen to account for as much as 60% of variability in other complex traits, such as obesity.

Pleasure in a pill

The number of genes that influence the female orgasm remains unknown. But researchers reason that comparing the DNA of women who always orgasm with that of those who never do could shed light on the biological pathway behind the process. Drugs could then be developed to target the most influential genes or gene products in this pathway.

Medications for male erectile problems, such as Pfizer's Viagra (sildenafil citrate), have already given men more options, says London-based relationship therapist Ruth Mitchell. But she says women lack a similarly popular and effective treatment.

Even with the promise of drugs, Mitchell cautions that many factors besides biology affect the ability to orgasm. "There's such a huge impact from conditioning and expectation," she says.