A new study examines “orgasmability” to determine whether it serves a purpose or is just an evolutionary accident
There may be few questions of human sexuality more rancorous than those about the female orgasm. Scientists agree that women probably started having orgasms as a by-product of men having them, similar to how men have nipples because women have them. As Elisabeth Lloyd, a philosopher of science and theoretical biologist at Indiana University put it in her 2005 book The Case of the Female Orgasm: Bias in the Science of Evolution: “Females get the erectile and nervous tissue necessary for orgasm in virtue of the strong, ongoing selective pressure on males for the sperm delivery system of male orgasm and ejaculation.” But why we ladies still have orgasms is hotly debated.
Male orgasms exist, it’s widely believed, to encourage men to spread their seed. On face value, it would be easy to say that women orgasm for the same reason: to encourage them to have sex and make babies. But in practice, compared to male orgasm, female orgasm is very difficult to achieve. There’s a lot of variation even within individual women, and 10 percent of women never have them at all. And, unlike male orgasm, female orgasm isn’t a prerequisite for pregnancy.
So why do women have orgasms at all? There are two firmly opposed camps on this question. The first group proposes that it has an adaptive function in one of three categories: pair bonding, mate selection and enhanced fertility. I’ll break these down. The pair-bonding theory suggests that female orgasm bonds partners, ensuring two parents for the offspring, while mate selection offers that women use orgasm as a sort of litmus test for “quality” partners. The enhanced fertility theory, meanwhile, proposes that uterine contractions during female orgasm help to “suck up” sperm into the uterus.
The by-product camp, on the other hand, claims that female orgasms are to this day an incidental by-product of male orgasm, not an evolutionary adaption. “There’s no documented connection between women who have orgasm at all, or faster, having more or better offspring,” Lloyd says.
The schism between the two camps deepened this month with the publication of a new study of twins and siblings in Animal Behavior that seems to rule out the by-product theory of female orgasm. Researchers Brendan Zietsch at the University of Queensland in Australia and Pekka Santtila at Abo Akedemi University in Finland asked 10,000 Finnish female and male twins and siblings to report on their “orgasmability” (their word, not mine). They looked for similarities in orgasm function between female and male twins. If the by-product theory of female orgasm is true, they say, this similarity should exist. Due to the inherent differences in orgasm between women and men, females were asked to report how often they had orgasms during sex and how difficult they were to achieve, while males were asked how long it took them to reach orgasm during the act and how often they felt they ejaculated too quickly or too slowly.
Zietsch and Santtila found strong orgasmability correlations among same-sex identical twins, and weaker yet still significant similarities between same-sex non-identical twins and siblings. However, they found zero correlation in orgasm function between opposite-sex twins. “We show that while male and female orgasmic function are influenced by genes, there is no cross-sex correlation in orgasmic function — women’s orgasmability doesn’t correlate with their brother’s orgasmability,” explains Zietsch. “As such, there is no path by which selection on male orgasm can be transferred to female orgasm, in which case the by-product theory cannot work.”…