Genes Shown to Be Key in Orgasm

A woman’s ability to experience orgasm is significantly influenced by her genes, according to a study of thousands of twins published online today by the British journal Biology Letters.

The study found that genetic factors accounted for 45% of variation among women in the ease of orgasm from masturbation, with the rest due to differences in environment.

The occurrence of orgasm during intercourse was also genetically influenced, although less so, with 34% of variation due to genes.

The researchers from London’s St. Thomas’ Hospital and Keele University in England mailed questionnaires to 3,654 sets of female twins ages 19 to 83.

Each woman was asked two questions: “Overall, how frequently do you experience an orgasm during intercourse?” and “How frequently do you experience an orgasm during masturbation by yourself or a partner?”

The women replied using a seven-point scale that ranged from “unsure/never” to “always.”

Of the 4,037 women who returned the questionnaires, 32% reported they never or rarely experienced an orgasm during intercourse, and 21% said they never or rarely experienced one through masturbation.

These frequencies are in line with other surveys of women’s sexuality, said Dr. Tim Spector, director of the Twin Research Unit at St. Thomas’ Hospital and the principal author of the study.

A study of Australian twins published this year also found a significant genetic contribution to how women experienced orgasms.

To calculate the influence of genes, scientists in the current study used a classic technique comparing responses of identical twins with those of nonidentical twins. Responses were available from 683 sets of identical twins and 714 sets of nonidentical twins.

Since the genetic material of identical twins is essentially the same, the differences between them are thought to be a result of differences in their environments.

Nonidentical twins, however, share half of their genes on average, which means that both genes and environment account for differences between them.

The authors said they did not know what the underlying genes were nor what their functions might be. But given the complexity of the orgasm, “it’s likely that many different genes are involved -- we’re not looking for just one gene but tens or maybe hundreds of genes,” Spector said.

Barry R. Komisaruk, a professor of psychology at Rutgers University in New Jersey, said it was plausible that genes influenced a woman’s experience with orgasms.

Genes may, for example, affect several pathways of nerves that connect the female genital area and the brain, said Komisaruk, who researches the female orgasm. Or they could affect engorgement of the genital area, levels of hormones such as testosterone, or the release of neurochemicals that orchestrate desire and the experience of orgasm in the brain.

The possible contributing factors are especially plentiful in intercourse, because another person is involved, he said.

“That is so complex -- it is one of the most complex interactions that a human experiences,” Komisaruk said.