Now that I’ve written at some length about the curious evolution of the male reproductive system in our species, I thought it only right to devote a column to the natural origins of a biological mechanism that doesn’t involve the Y chromosome. Well, at least it doesn’t have to. Needless to say, the subject of female orgasms isn’t exactly my cup of tea. As a gay man, it’s always seemed rather exotic and foreign to me, sort of like decorative basket-weaving in a small African village. As far as I know, I’ve never even been in the same room as a woman having an orgasm, let alone given a woman one.
Fortunately, a handful of dedicated researchers have spent a lot more time on this issue than I have. Yet it’s fair to say that even these scientists are still scratching their heads over the evolution of the female orgasm. Before we get into the nitty-gritty, let’s make sure we’re all on the same page about what a female orgasm actually is. A good working definition can be found in a 2004 report in the Annual Review of Sex Research . According to University of Texas at Austin psychologist Cindy Meston and her colleagues:
Female orgasm is a variable, transient peak sensation of intense pleasure, creating an altered state of consciousness, usually with an initiation accompanied by involuntary, rhythmic contractions of the pelvic striated circumvaginal musculature, often with concomitant uterine and anal contractions and myotonia that resolves the sexually induced vasocongestion (sometimes only partially), generally with an induction of well-being and contentment.
Actually, in light of that description and sans the female bits, perhaps it’s not entirely foreign to me after all. In fact, in terms of evolutionary function, women having orgasms with men is almost as puzzling as men having orgasms with men. How many of us human beings were conceived in the wake of our mothers having orgasms may never be known, but the same mystery doesn’t surround our fathers’ orgasms that day. Unlike men, women don’t need to have an orgasm in order to propagate their genes.
Thus, from a biological perspective, the “adaptive function” of the female orgasm is still hotly contested. Some theorists, including the late and legendary Stephen J. Gould , have claimed that it serves no purpose at all, but is instead only a quirky, functionless by-product of the ejaculatory response in males. In one of his cleverer pieces, re-titled “Male Nipples and Clitoral Ripples,” Gould fleshed out an old argument first made by anthropologist Donald Symons. In 1979, Symons noted that early in embryological development, males and females share the same basic body plan. As a serendipitous consequence of selection for male ejaculation (which in straight men serves obvious reproductive purposes), some of the shared connective tissue and nervous system pathways in females were “accidentally” shaped for pleasure by evolution, too, leading happily to the occasional orgasm in sexually mature females. The clitoris is essentially the female version of the penis, since the two derive from the same embryological substrate. This also explains why female orgasms are achieved more by clitoral than vaginal stimulation.
Lest you think the by-product hypothesis was propagandistic, cooked up in some musky faculty lounge by ivory tower misogynists, note that, for years, the main advocate of this position has been a female philosopher of biology named Elisabeth Lloyd. In fact, it was Lloyd who had initially given Gould his lead on Symons’s thinking on the subject and who would later write a book strongly endorsing the by-product hypothesis called The Case of the Female Orgasm (Harvard University Press, 2005). Lloyd’s book was roasted by many evolutionary thinkers because of the not-so-subtle feminist undertones in her writing—basically she argues that female carnal bliss has been liberated from the ugly realities of reproductive biology. Her position? Ladies, go out—or stay home alone, your choice—and enjoy yourselves, your sexuality is about more than just baby-making. But over the years, other empirically minded detectives have been working on this case as well, and many have begun to question the by-product account, claiming instead that the evidence does indeed point to some possible adaptive function of female orgasm.
So to help you play along in the role of orgasmic sleuth, here are a few suggestive clues that researchers in this area have been trying to piece together into a plausible evolutionary story:
Clue # 1: Twin-based evidence shows that orgasm frequency has a modest hereditable component. That is to say, uncomfortable as it may be to think of your flushed-faced grandmother writhing and moaning in ecstasy, there is a definite genetic contribution to female orgasm. (To help “unsee” these unsettling images shivering on the branches of your family tree, think on the bright side: female orgasms tend to decrease with age, so we’re talking mostly about only young, still-hot grandmas.) Hereditary factors account for only a third of the population-level variance in female orgasm, however.
Clue # 2: Most women report that they are more likely to experience an orgasm while masturbating than during sexual intercourse with a male partner, and importantly such masturbatory orgasms do not always hinge on simulating penile-vaginal sex. However, as University of Washington psychologist David Barash notes, “just because something (e.g., female orgasm) can be achieved in diverse ways (e.g., masturbation) does not argue against it having evolved because it is particularly adaptive in a specific, different context (e.g., heterosexual intercourse).”
Clue # 3: Furthermore, educated women are more likely to report having masturbatory orgasms—but are no more likely to experience coital orgasms than are less educated women. Religiosity is another social mediator: religious women tend to have less frequent orgasms than nonreligious ones (or at least they report having fewer).
Clue # 4: Using self-report data collected from college-aged American females, researchers such as Florida Atlantic University psychologist Todd Shackelford and University of New Mexico biologist Randy Thornhill have uncovered a positive correlation between frequency of orgasm and the physical attractiveness of male partners, with attractiveness being measured by subjective ratings as well as by indices of facial symmetry. Recall that, in “genetic fitness” terms, attractiveness tends to correlate positively with health and overall genetic value.
Clue # 5: There is some physiological evidence that female orgasm leads to the retention of more and/or better-quality sperm among a single ejaculate. I don’t think I can put it any better than Birkbeck University of London psychologists Danielle Cohen and Jay Belsky: “During the female copulatory orgasm the cervix rhythmically dips into the semen pool, thereby increasing sperm retention (by about 5 percent) relative to intercourse without orgasm, along with the probability of conception.” But as Lloyd points out, most references to these classic “data” on the “uterine upsuck” properties of female orgasm derive from a single participant and were part of an old study done back in 1970. Nevertheless, tellingly, a woman’s “desire to conceive” leads to more frequent self-reported orgasms during sex, and female orgasms are also most likely to occur during the most fertile period of the menstrual cycle.
Clue # 6: In a recent study by University of Groningen psychologist Thomas Pollet and co-author Daniel Nettle, Chinese women who were dating or married to wealthy male partners reported having orgasms more frequently than women whose partners made less. (“When having sex with your current partner, how often do you have an orgasm?” On an ordinal scale: 1=never ; 2=rarely; 3=sometimes; 4=often; 5=always .) That is to say, male partner income correlated strongly and positively with female orgasm frequency, and this income effect panned out even after the authors controlled for (ruled out) a host of extraneous variables, including health, happiness, education, the woman’s personal income and “westernization.” In any event, women may not be the only females in the animal kingdom whose orgasms are linked to the status and wealth of their male sexual partners. Japanese macaque females display the “orgasm-like” clutching reaction more often when they’re mating with high-status males. There’s no data yet on whether or not they also bite their lower lips in the process.
Together, these findings seemingly vindicate evolutionary psychologist David Barash, a vocal critic of Elisabeth Lloyd who has been arguing that female orgasm “is a signal whereby a female’s body tells her brain that she is sexually engaged with a dominant individual.” Pollet and Nettle point out, for example, that female orgasm may be linked to male income because money (resources) is a reliable indicator of the male’s long-term investing in offspring and it may also reflect desirable underlying genetic characteristics. In this light, female orgasm may serve an emotional bonding role, motivating sexual behavior—and hence conception—with high status males.
I wish there were a climax to the story, but as you see, the tale of the natural origins of female orgasm is a messy one. Some of the findings and logic favor the by-product hypothesis, whereas recent data on male quality and orgasm frequency cast reasonable doubt on the “functionless” accounts. Female orgasm is unfortunately one of those questions that do not easily lend themselves to controlled experimentation in the laboratory. One can’t, of course, randomly assign women to have sex with males differing in status and attractiveness to see if they orgasm or not (those pesky university ethics review boards). So I leave it to you, dear readers, to cobble together a once-upon-a-time story of female orgasm featuring the clues I’ve left you.
In this column presented by Scientific American Mind magazine, research psychologist Jesse Bering of Queen's University Belfast ponders some of the more obscure aspects of everyday human behavior. Ever wonder why yawning is contagious, why we point with our index fingers instead of our thumbs or whether being breastfed as an infant influences your sexual preferences as an adult? Get a closer look at the latest data as “Bering in Mind” tackles these and other quirky questions about human nature. Sign up for the RSS feed or friend Dr. Bering on Facebook and never miss an installment again. For articles published prior to September 29, 2009, click here: older Bering in Mind columns.