Why Do Women Orgasm?

By David P. Barash and Dr. Judith Eve Lipton, National Sexuality Resource Center. Posted August 22, 2009.

It is sometimes claimed that we have reached the "end of science," that we pretty much know all there is to be known, and as a result, from now on it is simply a question of mopping up. Not so. Some of the greatest, most challenging scientific conundrums are very close to home, among human beings: our species, our mysteries, ourselves. As it happens these enigmas are especially real when it comes to women’s sexuality.

Here are some examples:

The first notable mystery begins when a girl becomes a woman: menstruation. Although a few other species bleed slightly at midcycle, no other organism does so as prominently as Homo sapiens. Breast development is another perplexity. Although we take it for granted that women have conspicuous breast tissue even when not nursing, no other mammal is comparably bosomed. Only human beings are blessed (or, in the opinion of some, cursed) with prominent nonlactating breasts.

The mysteries continue. Go to a zoo and take a look at the chimpanzees, gorillas, or baboons (or indeed, nearly any nonhuman primate) -- there is no question when an adult female is ovulating. It is as clear as the bright pink cauliflower on her behind.  Not so for our own species. Given the great importance -- socially, biologically, evolutionarily -- of reproduction, and thus of ovulation, it is extraordinary and, as yet, unexplained why even now, in our medically sophisticated twenty-first century, it is exceedingly difficult to tell something so basic as when a woman is fertile. For reasons unknown human beings conceal their ovulation and are unique among mammals in doing so. Not only that, but in the great majority of cases, the exact time of a woman’s ovulation is even hidden from herself. Why the deep, dark secret? As with menstruation and nonlactating breasts hypotheses abound, but no one knows the answer.

Ditto for female orgasm. Its male counterpart is a no-brainer (almost literally!), since without ejaculation there would be no fatherhood and thus no evolutionary success.  But the data are quite clear. There is no correlation between female orgasm and female fitness in the evolutionary sense; in other words, orgasmic women are no more successful, reproductively, than their less fortunate, nonorgasmic "sisters." So why does female orgasm occur at all?

Proceeding along the trajectory of a woman’s life, we come to yet another mystery: menopause. By around age fifty a woman can anticipate that she will cease ovulating. Why does reproduction inevitably end, even for the healthiest women, at a time in middle age when many can anticipate several decades of continued life? This is especially perplexing since reproductive success is the name of the Darwinian game, and simple calculations show that producing just one additional child, compounded over time, would convey a huge evolutionary advantage. Perhaps it is not so surprising, then, that menopause -- a cross-cultural human universal -- is not shared by any other living thing except possibly for the short-finned pilot whale . . . but of course, you already knew that!

These and other traits are fundamental to being human, yet their basis is neither understood by scientists nor, for the most part, even acknowledged by the public as the puzzles that they are. In our book How Women Got Their Curves and Other Just-So Stories, we explored these and other sexual unknowns, describing some of the scientific hypotheses that have been proposed, while also suggesting some new ideas of our own. In short, there are more things in human sexual biology than are dreamt of in our philosophy or -- more to the point -- known by our science.

But don’t get the wrong idea, Horatio. Mystery is not the same as mysticism, and we are not referring to some sort of ineffable, spiritualistic claptrap beyond the reach of natural law or human understanding. Just as a "weed" is a plant that hasn’t yet been assigned a value, the various womanly mysteries are simply scientific questions waiting for answers. Our perspective, however, is one that many readers will find unusual.

Thus, when we ask "why" women conceal their ovulation, for example, we aren’t looking into the physiological mechanisms involved but, rather, we are asking how, if at all, individuals who keep this particular part of their biology under wraps have come to leave more descendants than others who were more public about their potential reproductive status. This approach is familiar to evolutionary biologists, less so to the thinking of most anatomists, physiologists, and so forth. Not that these scientists aren’t likely to be "evolutionary" in their thinking; rather, they are more prone to ask questions -- and to answer them -- in terms of immediate causal mechanisms. Instead, we raise questions -- and answer them -- in evolutionary terms. The underlying conceptual theme is therefore: "In what way has _______ (menstruation, nonlactating breasts, female orgasm, menopause, etc.) contributed to the fitness of human beings, especially among our ancestors, thus explaining why these traits evolved?"

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