Homo Mysterious: Evolutionary Puzzles of Human Nature (8 page)

But human beings might be different, at least somewhat. There is no other species of mammal in which the male contributes so much to rearing successful offspring. As a result, it behooves
women to be attractive to men, and not just vice versa, as in most traditional evolutionary models of mate selection. The greater the significance of male investment for the success of offspring, the more important it is for females to signal their quality to any prospective mates. And maybe growing full breasts (regardless of what may have initiated this trend) is one way they accomplish this.

Female sexuality undoubtedly offers a range of evolutionary mysteries, with each mystery susceptible to a variety of explanations. In the next chapter, we examine two more such mysteries, while we also explore some of their male counterparts.

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(2), 174–192; Rhodes, G., Yoshikawa, S., Palermo, R., Simmons, L. W., Peters, M., Lee, K., et al. (2007). Perceived health contributes to the attractiveness of facial symmetry, averageness, and sexual dimorphism.
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(1), 117–144.

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. Moller, A. P., Soler, M., & Thornhill, R. (1995). Breast asymmetry, sexual selection, and human reproductive success.
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C
HAPTER
T
HREE
Sexual Mysteries II: Female Orgasm, Menopause, and Men

NEXT: FEMALE ORGASM
. What is
that
all about?

There is a Spanish expression, “Hay que gozar mucho para desquitarse de la vida” (
You need to have a lot of fun to get even with life
). Whether or not you agree, it isn’t enough to say that female orgasm exists because it is great fun, or a gift from a benevolent God with an assist from a satisfying partner—when not self-induced—along with a delightfully cooperating personal physiology. Life throws us a lot of curveballs, making it tempting to conclude that some of the good stuff, like orgasms, are simply there to make up for it. Not so fast.

There is no doubt that orgasm feels good. Think of Meg Ryan’s famous simulated orgasm-in-the-restaurant scene in the movie
When Harry Met Sally
(after which a middle-aged diner says to the waiter, “I’ll have what she’s having”). We’ll look at fake orgasm later; for now, our point is simply that the real thing cannot simply be written off as good fortune or a surprising culinary consequence of choosing the right menu item while having a meal with Billy Crystal. Nowhere in the biological world is pleasure bestowed cheaply or randomly or out of mere cosmic generosity.

When asked, many women say that orgasm is a great tension reliever. True enough, but this doesn’t mean that tension relief is the
reason
for orgasm, since if sexual tension hadn’t accumulated in the first place, it wouldn’t have needed releasing. And why do it that way?

The reality is that female orgasm is a contentious, unsolved mystery among evolutionary biologists, simply because its adaptive significance—its biological payoff—is obscure.

Events on the male side pretty much speak for themselves. Even though orgasm (a subjectively experienced phenomenon) is technically different from ejaculation (expulsion of semen from the body), it occasions no great surprise that for men the two are tightly connected, and that evolution has doubtless contrived to use the former as a carrot, inducing men to engage in the latter. But what about women?

Of course, not all women experience orgasm, and that is part of the mystery, although not as one might think: The enigma of female orgasm is
not
why some women don’t climax but why some
do
. The data are quite clear that unlike its male counterpart, female orgasm isn’t necessary for reproduction; among the many complaints of nonorgasmic women, inability to conceive is not one.

For generations, old and young wives’ tales—husbands’, too—along with scores of Victorian romance novels claimed that there was some sort of connection between a woman “really giving” herself and finally becoming pregnant. And to be sure, it is easy to speculate how female orgasm might facilitate fertilization, especially if the waves of muscular contraction provide greater access of sperm to egg. The problem, however, is that most of these contractions go in the wrong direction! It has alternatively been claimed that uterine contractions during orgasm literally generate a suction effect, which draws semen up toward the fallopian tubes. There may yet be some truth to this rather inelegantly named “uterine upsuck” hypothesis, which was generated by heroic laboratory research in which a radio telemetry device was inserted
into a uterus, thereby revealing a vacuum cleaner–like negative pressure following orgasm.
¹
This “finding,” however, was based on an unacceptably small sample size: one woman!

Moreover, even if uterine upsuck turns out to be a valid phenomenon, it is far from what scientists call a “robust” one, or else it would have been noted previously. More to the point, it would have generated a cause-and-effect relationship between female orgasm and subsequent pregnancy, which simply does not exist.

It has also been suggested—although again, the data are inconclusive—that orgasm reduces the amount of “flow-back” (the leakage of semen out of a woman’s reproductive tract), thereby increasing the likelihood that fertilization will be achieved by the partner who helped induce that orgasm.
²
But this, too, is controversial, based on a very small sample of remarkably cooperative couples.

Although there are, in theory, many ways by which female orgasm could facilitate fertilization (including a range of possible biochemical effects along with physical assistance to sperm or egg), there is currently no evidence that orgasmic women produce more babies, or better ones, than their less fortunate “sisters.” And of course, in vitro fertilization further italicizes that when it comes to baby making, female orgasm is simply not a physiologic or anatomic prerequisite.

On the other hand, female orgasms are unquestionably real and are, if anything, more dramatic than their male counterparts, especially given a woman’s capacity for multiple orgasms. Given that there are no free lunches in biology, the question presents itself: Why orgasm?

The redoubtable Desmond Morris, whose fertile imagination gave us the “buttocks mimic” hypothesis for the evolution of breasts, unburdened himself of yet another howler, proposing that orgasm is natural selection’s way of keeping a woman horizontal after sex, which in turn supposedly makes fertilization more likely. This “knock-down” hypothesis has problems. For one, despite
substantial efforts, it has never been demonstrated that postcoital positions influence fertilization. And if they did, there are lots of possible ways of inducing individuals to remain prone, or supine, or on one’s side, etc., such as reducing blood pressure after sex, without any particular subjective bells and whistles. Moreover, if our upright posture somehow necessitates such an intervention, then other upright animals should behave similarly, yet kangaroos and wallabies pop right up and hop about immediately after copulating.

It might similarly be suggested that under more “natural” conditions, orgasm would have made a postcopulatory woman less conspicuous to predators, perhaps by making her somewhat less physically active following sex. The problem here is that if the strategic goal is to remain below the perceptual horizon of potential predators, who might have been attracted to all that commotion in the bushes, it would be far more efficient to eliminate female orgasm altogether, which seems likely to have contributed significantly to the ruckus in the first place. If our ancient ancestors were being prodded by natural selection to keep from being detected—by potentially jealous conspecifics as well as predators—they would seem better advised to keep quiet and minimally aroused all along.

Another possibility, superficially plausible but ultimately unconvincing, is that orgasm is an evolutionary tactic to induce women to copulate at all. The biggest problem here is that there are many animals that lack anything resembling the bells and whistles of female orgasm, and for whom copulation is a dutiful but unexciting act. Instead, they copulate with the same resignation (occasionally mixed with moderate enthusiasm) with which they might build a nest, feed their offspring, or defecate. Orgasm clearly isn’t a prerequisite for copulation. Why should we, more than any other species, require profound waves of cataclysmic ecstasy to do what other animals do simply as a matter of course, like scratching when they itch?

Maybe our extraordinary development of female orgasm—and although it is not unique to
Homo sapiens
, it is without doubt uniquely elaborated and more fully developed in our species than in any other—has something to do with that other uniquely human trait, consciousness. In the previous chapter we considered the
hypothesis that concealed ovulation might have evolved because prehistoric women were aware of the downsides of pregnancy, causing natural selection to favor those women who couldn’t tell when they were fertile. Isn’t it also possible that this same awareness, on the part of ancestral women, would have made them hesitant to engage in sex at all?