Come Again?
Much as women’s breasts have fascinated evolution-minded theorists, the female orgasm has confounded them. Like breasts, female orgasm is a major head-scratcher for mainstream narratives of human sexual evolution. It’s not necessary for conception, so why should it exist at all? For a long time, scientists claimed that women were the only female animals to experience orgasm. But once female biologists and primatologists arrived on the scene, it became obvious that many female primates were having orgasms.
The underlying motivation for claiming that female orgasm was unique to human beings probably lay in the role it played in the standard narrative. According to this view, orgasm evolved in the human female to facilitate and sustain the long-term pair bond at the heart of the nuclear family.18 Once you’ve swallowed that story, it becomes problematic to admit that the females of other primate species are orgasmic, too. Your problem gets worse if the most orgasmic species happen to be the most promiscuous as well, which appeares to be the case.
As Alan Dixson writes, this monogamy-maintenance explanation for female orgasm “seems farfetched. After all,” he writes, “females of other primate species, and particularly those with multimale–multifemale [promiscuous] mating systems such as macaques and chimpanzees, exhibit orgasmic responses in the absence of such bonding or the formation of stable family units.” On the other hand, Dixson goes on to note, “Gibbons, which are primarily monogamous, do not exhibit obvious signs of female orgasm.”19 Although Dixson classifies humans as mildly polygynous in his survey of primate sexuality, he seems to have doubts, as when he writes, “One might argue that … the female’s orgasm is rewarding, increases her willingness to copulate with a variety of males rather than one partner, and thus promotes sperm competition.”20
Donald Symons and others have argued that “orgasm is most parsimoniously interpreted as a potential all female mammals possess.” What helps realize this “potential” in some human societies, argues Symons, are “techniques of foreplay and intercourse [that] provide sufficiently intense and uninterrupted stimulation for females to orgasm.”21 In other words, Symons thinks women have more orgasms than mares simply because men are better lovers than stallions. Stomp your foot three times if you believe this.
In support of his theory, Symons cites studies like Kinsey’s showing that fewer than half of women questioned (Americans in the 1950s) experienced orgasm at least nine out of ten times they had intercourse, whereas in other societies (he refers to Mangaia, in the South Pacific), elaborate and extended sexual play result in nearly universal orgasm for women. “Orgasm,” Symons concludes, “never is considered to be a spontaneous and inevitable occurrence for females as it always is for males.” For Symons, Stephen Jay Gould, Elisabeth Lloyd,22 and others, some women have orgasms sometimes because all men do every time. For them, the female orgasm is the equivalent of male nipples: a structural echo without function in one sex of a trait vital in the other.
Given all the energy required to get there, it’s surprising that the female reproductive tract is not a particularly welcoming place for sperm cells. Researchers Robin Baker and Mark Bellis found that approximately 35 percent of the sperm are ejected within half an hour of intercourse and those that remain are anything but home free.23 The female’s body perceives sperm as antigens (foreign bodies) that are promptly attacked by anti-sperm leucocytes, which outnumber sperm 100:1. Only one in 14 million ejaculated human sperm even reach the oviduct.24 In addition to the obstacles imposed by the female’s body, even those lucky few sperm are going to run into competition from other males (at least, if our model of human sexuality has any validity).
But while presenting obstacles to most sperm, the woman’s body can assist others. There is striking evidence that the female reproductive system is capable of making subtle judgments based upon the chemical signature of different men’s sperm cells. These assessments may go well beyond general health to the subtleties of immunological compatibility. The genetic compatibility of different men with a given woman means that sperm quality is a relative characteristic. Thus, as Anne Pusey explains, “Females may benefit from sampling many males, and different females will not necessarily benefit from mating with the same ‘high quality’ male.”25
This is a crucially important point. Not every “high quality” male would be a good match for any specific woman—even on a purely biological level. Because of the complexities of how the two sets of parental DNA interact in fertilization, a man who appears to be of superior mate value (square jaw, symmetrical body, good job, firm handshake, Platinum AMEX card) may in fact be a poor genetic match for a particular woman. So, a woman (and ultimately, her child) may benefit by “sampling many males” and letting her body decide whose sperm fertilizes her. Her body, in other words, might be better informed than her conscious mind.
So, in terms of reproduction, the “fitness” of our prehistoric male ancestors was not decided in the external social world, where conventional theories tell us men competed for mates in struggles for status and material wealth. Rather, paternity was determined in the inner world of the female reproductive tract where every woman is equipped with mechanisms for choosing among potential fathers at a cellular level. Remember this next time you read something like, “The predisposition for influence, substance and prestige are all merely expressions of a male positioning himself to acquire women with whom to mate,” or, “Mate competition will involve contests over resources [men’s] wives will need to raise children.”26 This may well be the situation for most people today, but our bodies suggest our ancestors faced an entirely different scenario.
Sperm competition is best understood not as a sprint to the egg, but a race over hurdles. Aside from the anti-sperm leucocytes mentioned previously, anatomical and physiological obstacles are in the vagina, cervix, and on the surface of the ovum itself. The complexity of the human cervix suggests it evolved to filter the sperm of various males. Concerning macaques (highly promiscuous monkeys) and humans, Dixson writes: “In the genus Macaca, all species of which are considered to have multimale-multifemale mating systems, the cervix is especially complex in structure…. The evidence pertaining to human beings and macaque females,” he continues, “indicates that the cervix acts both as a filtering mechanism and as a temporary reservoir for spermatozoa during their migration into the uterus.”27 As with the complex penis and external testicles in the male, the elaborate filtering design of the human cervix points toward promiscuity in our ancestors.
The idea that female choice (conscious or not) can happen after or during intercourse rather than as part of an elaborate precopulatory courtship ritual turns the standard narrative inside out and upside down. If the female’s reproductive system has evolved intricate mechanisms for filtering and rejecting the sperm cells of some men while helping along those of a man who meets criteria of which she may be utterly unaware, Darwin’s “coy female” starts looking like what she is: an anachronistic male fantasy.
But Darwin may have suspected more than he let on concerning postcopulatory mechanisms of sexual selection. Any discussion of human sexual behavior or the evolutionary implications of our genital morphology would have been extremely controversial in 1871, to put it mildly. Just imagine, as Dixson does, “what would have occurred if The Descent of Man had included a detailed exposition of the evolution of the penis and testes or descriptions of the various copulatory postures and patterns employed by animals and human beings.”28
No one can blame Darwin for opting not to include chapters on the evolution of the penis and vagina in his already explosive work. But a century and a half is a long time for discretion and cultural bias to keep smothering scientific fact. To Meredith Small, the story of the female’s role in conception is a miniature of the overall narrative. She sees the popular understanding of conception as “an outdated allegory of human sexuality” featuring the male as “aggressor, persuader, conqueror.” Recent research on human fertilization suggests something of a role reversal. Small suggests the ovum “reaches out and envelops reluctant sperm.” “Female biology,” she concludes, “even at the level of egg and sperm interaction, doesn’t necessarily dictate a docile stance.”29
In addition to enveloping eggs, a cervix that filters or favors sperm, and vaginal contractions that may expel the sperm of one man while boosting that of another, women’s orgasms provoke changes in vaginal acidity. These changes appear to assist the sperm cells of the lucky guy who provoked the orgasm. The environment at the cervical opening tends to be highly acidic and thus hostile to sperm cells. The alkaline pH of semen protects the spermatozoa in this environment for a while, but the protection is short-lived; most of the sperm cells are viable within the vagina for only a few hours, so these changes in acidity alter the vaginal environment in ways that can favor sperm that arrive with the female’s orgasm.
The benefits may run both ways. Recent research suggests women who do not use condoms are less likely to suffer from depression than either women who do use condoms or who are not sexually active. Psychologist Gordon Gallup’s initial survey of 293 women (data congruent with those from another survey still to be published that included 700 women) found that women can develop a “chemical dependency” on the boost they get from the testosterone, estrogen, prostaglandins, and other hormones contained in semen.
These chemicals enter the woman’s bloodstream through the vaginal wall.30
If it’s true that multiple mating was common in human evolution, the apparent mismatch between the relatively quick male orgasmic response and the so-called “delayed” female response makes sense (note how the female response is “delayed” only if the male’s is assumed to be “right on time”). The male’s quick orgasm lessens the chances of being interrupted by predators or other males (survival of the quickest!), while the female and her child would benefit by exercising some preconscious control over which spermatozoa would be most likely to fertilize her ovum.
Prolactin and the other hormones released at orgasm appear to trigger very different responses in men and women. While a man is likely to require a prolonged refractory (or recovery) period immediately after an orgasm (and maybe a sandwich and a beer as well), thus getting him out of the way of other males, many women are willing and able to continue sexual activity well beyond a “starter orgasm.”
It’s worth repeating that primate species with orgasmic females tend to be promiscuous. Given the great variability of mating behavior—even just among the apes—this is highly significant. While monogamous gibbons have rarely been seen copulating, so infrequent and silent is their intercourse, female chimps and bonobos go wild regularly and shamelessly. Females often mate with every male they can find, copulating far more than is necessary for reproduction.
Goodall reported seeing one female at Gombe who mated fifty times in a single day.
Echoing the Kama Sutra, Sherfey isn’t shy about the implications of this mismatch of orgasmic capacity between human males and females, writing: “The sexual hunger of the female, and her capacity for copulation completely exceeds that of any male,” and, “To all intents and purposes, the human female is sexually insatiable. …” That may or may not be, but it cannot be denied that the design of the human female’s reproductive system is far from what the standard narrative predicts, and thus demands radical rethinking of the evolution of female sexuality.