The Study of O
The female orgasm as evolution's happy accident.
Elisabeth Lloyd, a soft-spoken philosopher of biology, didn't expect to serve up jokes on Saturday Night Liv e when she published an academic book late last month. But The Case of the Female Orgasm hit a cultural G spot. After the New York Times featured Lloyd in last Tuesday's science section, her phone started ringing, and by Thursday she was chatting about orgasms with Barbara Walters and the other women on ABC's The View. Saturday Night Live parodied the book as a "case of" mystery that's "a real departure for The Hardy Boys."
Why the fuss? Lloyd's central claim is not new. But her study of evolution and orgasm offers the most thorough and serious treatment of the subject to date—and strongly rejects the claim that orgasm in women serves an evolutionary purpose. Lloyd has scrutinized 21 evolutionary accounts of female orgasm and makes a convincing case for the single account that treats orgasm as a happy accident, a byproduct of the role that male orgasm plays in reproduction and the sharing of early embryonic tissue by the male and female genitalia. The other 20 theories she dismisses as illogical or incompatible with data on women's sexuality. This time the press has it right. Lloyd's analysis is worth all the attention. She hasn't definitively settled the debate: One new line of inquiry could pose a challenge to her thesis. But it probably wouldn't be a fatal one, so score one for the orgasm as pure pleasure.
That approach was first advanced in 1979 by anthropologist Donald Symons. He argued that orgasm is possible in women because it is crucial in men. Embryos of both sexes have a common body plan early on, so when male orgasm is selected for by evolution, female orgasm comes along for the ride. Symons' explanation, dubbed the "byproduct account," was never popular among biologists. Most believed that female orgasm must somehow contribute directly to women's reproductive success (in evolutionary terms, must be an adaptation). Nor did the work go over well with feminists, who thought it cast women's sexual experience as derivative of men's.
When Lloyd began to investigate the science of orgasm in 1984, she was impressed by Symons' work. She mentioned it to Stephen Jay Gould in 1986, while they were collaborating on a paper about species selection. Gould was intrigued and said he'd like to write up the byproduct account for his column in NaturalHistory. Lloyd shored up her documentation and handed Gould a 50-page, single-spaced manuscript—the seed that would eventually grow into her current book. When Gould's column "Freudian Slip" appeared in the February 1987 issue of Natural History, it set off an academic firestorm, provoking particularly aggressive attacks from John Alcock, a fervent proponent of adaptive explanation. It was Gould, not Lloyd, who was called on to defend the byproduct stance; Lloyd says that she did not then want the intense attention.
In the 1990s, Symons' theory largely receded from the spotlight. A new mini-genre of adaptive explanations that assume a link between female orgasm and reproductive success came to the fore. These "sperm competition" theories suggest that female orgasm somehow helps to draw sperm up through the cervix and uterus, thus aiding fertilization and reproduction. Many sociobiologists and scientists who study animal behavior now take sperm competition virtually for granted. According to Lloyd, fertility specialists sometimes tell women to lie on their backs and masturbate to orgasm after being artificially inseminated.
Lloyd dismisses the 20 theories of orgasm that assume an evolutionary purpose for female orgasm mainly because they overlook data on women's sexuality or make untenable leaps of logic. One well-known argument first advanced by zoologist Desmond Morris in 1967, for instance, claims that orgasm tires out women and causes them to lie immobile, on their backs, increasing the chances of fertilization by preventing sperm from leaking out. But as Lloyd notes, it is men, more than women, who tend to be sated and exhausted after orgasm. And women are more likely to reach orgasm when they're on top of their partners, in which case gravity doesn't work in favor of fertilization. Even when women climax lying on their backs, multiple studies have found no discernible upward flow of sperm—one experiment (by the sex researchers Masters and Johnson) seems to suggest that sperm is actually expelled from the uterus by orgasmic contractions. Throughout the book, Lloyd pinpoints the flaws in the theories with which she disagrees and emphasizes that there are no data correlating female orgasm with any aspect of fertility or reproductive success.
Lloyd endorses the alternate theory that orgasm is a byproduct because it meshes easily with the findings of sex research. Women tend to reach orgasm more quickly through masturbation than through heterosexual sex, for example, and when most masturbate, they don't mimic the act of penetration. And then of course there are all the women who don't reach orgasm through intercourse at all. All of this make far more sense if women's potential for orgasm is understood as separate from their potential for childbearing. Lloyd even gives the byproduct theory a new and appealing feminist twist: By not equating the pleasure of orgasm with the ability to have kids, she argues, it is more ur-woman than its competitors.
Lloyd's work has so far generated a few thoughtful responses and a host of misconceptions. (Read some of the ones rippling through the blogosphere, along with responses to them.) Where will the debate go next? Lloyd has successfully rebutted most of the key findings on which the orgasm-is-adaptive arguments currently depend. But research involving the hormone oxytocin could bolster the case that orgasm serves an evolutionary purpose and prompt a new round of wrangling. Oxytocin is best-known for the role it plays in spurring lactation and some of the contractions associated with labor. In a recent experiment, the uteri of women injected with oxytocin tended to draw in fluid (think sperm), suggesting a possible mechanism for enhanced fertility. Orgasm is associated with oxytocin release. But so is any kind of vaginal or cervical stimulation. In other words, it could be sex, and not orgasm, that is causing the oxytocin release that increases a woman's chances of getting pregnant. Which would be no help to the adaptationist camp after all.
To really boost their argument, adaptationists would need to show that substantially higher levels of oxytocin are consistently released with female orgasm; that this release is associated with a large increase of fluid movement through the reproductive tract; and that female orgasm is correlated with higher fertility rates and more babies. Even if strong data along those lines appear, the primary explanation for female orgasm could still be Symons' and Lloyd's—the common embryological origins of male and female genitalia. That is, small changes in either the clitoris or the nervous pathways associated with orgasm, which could have made orgasm more intense or easier to achieve, may be favored by some as-yet-undocumented selection pressure. But that adaptation could have nothing to do with the origins of female climax. Orgasm in women could still be first and foremost an offshoot of orgasm in men. In short, the burden of proof now lies with Lloyd's opponents.
Amanda Schaffer is a science and medical columnist for Slate.