Human Sexuality is Different

Human sex is similar to that of other animals (insects, birds and mammals) in most respects, but some aspects of our sex lives are as unusual as our intelligence, and that's probably not a coincidence. 

Unusual features of human sexual reproduction

Most of the ways our sexual reproduction is exceptional pertain to women:

• Cryptic ovulation — Not only do human females show no signs of ovulation to their partners, most women can't tell themselves when they're ovulating.  This may well be a specifically human trait. 
• Heavy menstruation — Relatively few other mammals menstruate at all, and no other mammals lose nearly as much blood as human females do.  In this, we are unique.
• Strong female orgasm — As far as we can tell (which is not all that far), few female mammals experience orgasm very strongly at all — human females seem way out at the extreme end of the spectrum in the intensity of their sexual pleasure. 
• Hazardous birth — Giving birth is far more difficult and dangerous for human females than for almost any other animal. 
• Prolonged dependence on parents — In order to survive and flourish, human children require dedicated parental nurturance for four to five years and then ongoing parental support for another five to fifteen years.  This is much longer than is the case for any other species. 
• Menopause — Most other mammals ovulate right up into old age, whereas human females can live as long after menopause as they live before it.  This is very unusual (only pilot whales are known at this point to experience menopause in a similar fashion). 
• Sexual embarrassment — Humans seem to be alone among animals in their large propensity to feel shame and embarrassment around sex.  Other animals, including social ones, seem to find it a perfectly comfortable activity, whether in public or private.

Revisiting cryptic ovulation

As we've discussed on the "normal sex" page, human females don't show any external sign that they're ovulating, which provides various reproductive advantages.  However, it would seem advantageous for a woman herself to remain aware of when she was fertile, so she could choose the most promising lover at that point to father a child.  It's one thing to conceal your fertility from males, but what advantage could derive from keeping it secret from yourself as well? 

Nancy Burly has advanced an interesting explanation:  If you were a smart woman and knew when you were ovulating, you'd also knew that getting pregnant had a very good chance of killing you (as has certainly been true through much of human prehistory and history), and so you'd just avoid sex at that point.  As a result, you wouldn't get pregnant, which means you wouldn't pass on the genes for being aware of ovulation.  A woman who didn't know when she was ovulating, on the other hand, would not find it so easy to avoid pregnancy and so would pass on her genes in spite of the danger. 

Why menstruation?

Human females are unique among all the animals we know of in losing a significant amount of blood in menses.  Human menstruation is expensive, dangerous and has no obvious benefit at all — so why hasn't the process of evolution selected it out of existence yet?  Biologists have devoted an enormous amount of ingenuity to coming up with theories, but none so far seems compelling. 

Leonard Shlain, for example, in his readable and intelligent Sex, Time and Power: How Women's Sexuality Shaped Human Evolution, ends up with an explanation that is so subtle as to be almost mystical — basically, he suggests that menstruation was selected for because it keeps us in touch with time. 

More compelling is Shlain's suggestion that women's need for iron resulting of their monthly loss of blood may have made relatively inefficient male hunting more important to a tribe's survival than has previously been understood.  Careful studies of male hunting have shown that it not generally an effective way to supply food for a tribe. 

So far, the jury is still out on why human females began menstruating heavily, and on why the trait has not long since disappeared. 

Women's powerful orgasms

To be effective in keeping her mate present and attentive throughout the month, as we have seen, a woman had to behave as if she might be fertile at any time (that is, she had to be sexually receptive).  At the same time, as she became more intelligent she would clearly realize, as Nancy Burly pointed out, how dangerous and painful pregnancy would be for her.  Only significant incentives would keep her having sex under such circumstances, if she had any choice in the matter. 

Thus, the pleasurable intensity of women's orgasms is strong evidence that prehistoric women did have a choice in the matter, because otherwise they would not have evolved such orgasms to keep them having sex.

That is to say, if men had been able simply to compel women to have sex within the kind of patriarchal framework that became common after the advent of agriculture, women's pleasure would have been unnecessary, and as the horrifying practice of female mutilation still testifies, female pleasure would have actively been selected against by the patriarchal males. 

To the extent, however, that women were in control of their sexual destiny, intelligent women would have chosen to avoid the dangers inherent in reproduction unless they were strongly tempted by a pwerful libido and intense pleasure.  The fact that human females seem to have evolved greater pleasure in sex than any other female animal argues that they did, in fact, enjoy a great deal of choice throughout most of our prehistory. 

Childbirth could be deadly

No other animal is as likely to die in childbirth as human females.  The reason is that as intelligence was increasingly selected for, our skulls got larger more rapidly than we seemed capable of evolving wider pelvises, and so our babies became too large for our birth canals. 

Part of the problem likely arose because we had to be effective upright runners — humans are not particularly fast, but we can outrun almost anything in terms of endurance — plains tribes in North America used to catch wild horses, for example, by chasing them on foot until the horses were to tired to go on. 

It's possible that wider hip bones that would better accomodate larger babies thus in many cases might have meant less capable runners, who then might not have survived to bear children in the first place.  Whether or not this was the case, we evolved to the point where reproduction was extremely dangerous for women. 

At the same time, we evolved quite a number of traits normally associated with providing females a lot of choice in mating, probably mainly because intelligent choice of mates by women was yielding more intelligent children much faster than other reproductive patterns, and so was being selected for strongly.  The dangers of child-bearing only reinforced the importance of making intelligent breeding decisions in order not only to have surviving offspring, but even to survive yourself. 

Human childhood is protracted

Human babies require more time than any other animal's young to become self-sufficient.  In particular, they require the full-time work of at least two adults for the first four to five years of their lives.  The main reason for this is the size of our brains and the long time that it takes for them to develop.  They end up and incredibly powerful tool and weapon, but they're very hard to produce! 

It has been suggested that both the prevalence of same-sex pair-bonding (also referred to as homosexuality) and the phenomenon of menopause among humans results from the need to have more than two adults in order to raise surviving children during times of hardship.  In times of famine, war and disaster, children with unencumbered grandparents and childless aunts and uncles would have survived where other children would not. 

Menopause creates wise-women

Another explanation of menopause proposed by Jared Diamond, based on his experience with the peoples of New Guinea, is that it allowed women to grow old rather than die in childbirth in late middle age.  He observed at first hand how crucially important old people were to the preliterate tribes he came to know, how they served as repositories of vast amounts of knowledge that often proved very useful and sometimes proved crucial to the tribe's very survival. 

Embarrassment

Other animals (dogs, for example)  do seem to experience an emotion like shame or embarrassment, but not around sex.  We humans are very unusual in our huge propensity to find sexual activity embarrassing. 

Interestingly, another thing we find acutely shameful is the feeling of embarrassment itself, which helps to explain why this emotion has received so little attention from psychologists and other researchers (see our shame page).  Evolutionary biologists, for example, would rather speak of our human tendency to prefer "private copulation" than refer to the emotions that produce such taboos. 

The idea of "private copulation" is reasonable shorthand for embarrassment in contemporary Western culture, but it's worth remembering that plenty of people have traditionally found (and still do find)  little difficulty being sexual in a safe and socially acceptable public context.  I'm reminded of Herodotus' comment about Egypt, that in all the countries he'd visited, only there and in Greece did people abstain from having sex in the public temples.  For him, that didn't appear to be an issue of privacy but rather one of religious tradition — the Greeks, for all their hangups, were not private about sex in the same sense that we are. 

It's also worth reminding ourselves that living accomodations in most of the world today, and throughout most of history, have simply not permitted people what Americans would think of as "privacy."  I remember in first-world Catholic Italy in the early 1970's, when I walked up the Gianiculum hill in Rome every afternoon after the archives closed, I would often pass Fiat 500s parked at the side of the road with steamy windows, rocking wildly as young people used them as "private" places to fuck.  The tiny cars may not have been private by American standards, but they were certainly far more private than cramped apartment where parents, grandparents and siblings might be crowded together in a few rooms. 

With a much broader scope than privacy, however, sexual embarrassment undoubtedly plays an important role in allowing us to pursue monogamous sexual behavior within a close-knit tribal context.  In many monogamous species, such as gibbons or ravens, couples live as isolated pairs, but humans typically live in close-knit groups where pair-bonds must co-exist with a complex of other social relationships.  Embarrassment is what keeps our powerful libidos in check, so that they don't wreak havoc with our social organization. 

At the same time, evolutionary logic also require that our libidos be able to overcome embarrassment and any taboos that embarrassment has ingrained in us whenever our ability to reproduce successfully is threatened. 

This places us uncomfortably between a rock and a hard place, in the middle of a tug-of-war between two powerful emotion complexes — our sexual desires on the one hand, and our sexual embarrassments on the other.  Both are designed to overcome the other under appropriate circumstances, but neither is designed to make us comfortable in the process. 

Learning to keep ourselves in balance between shame and desire, learning how to integrate the ambivalences of our lives, is one of the greatest challenges of being human.  There's no one right way to do it, in spite of what some people believe.  You have to do the work for yourself, just as no one else can learn to ride a bicycle for you. 

And yet, one of the main messages of this site is that you can find a balance around sex that makes you happy, without giving up things that are important to you, without oscillating between shame and desire.  You can live in sexual integrity! 

All of these unique features point to female choice of mates

If intelligence was of key importance to survival and selection, the ability to select for it intelligently would have created an incredibly advantageous feedback mechanism.  And in fact, looking at most of the unusual features of our sexuality described above, it does appear that the freedom of women to choose the fathers of their children was strongly selected for. 

The issue of mate selection raises the related question of polygyny, because without it, female choice would have been much less effective.  If many women could choose to breed with the most promising man in a group (and choose correctly), then his superior design would spread much more quickly than if only one woman was able to breed with him.  As Geoffrey Miller observes in The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (page 75), there is both physical and anthropological evidence to support the idea that humans were typically moderately polygynous through the hundreds of thousands of years of our prehistory. 

At the same time, because the raising of children required so much investment from both parents, surreptitious polygyny would have been the best solution for a woman — that is, have a devoted mate all to herself while sneaking access to more desirable genes to father her children.  This is quite a different style of polygyny than the male-controlled harem model we often use the term to describe, but it much better fits the extra-marital conception statistics reported on the previous page. 

In terms of deception and betrayal, this goes to show that women can benefit from sneaking off with secondary lovers just as readily as men. 

A more useful and positive conclusion that can be reached from looking at the evolutionary biology human sexuality, though, is that we definitely seem to have evolved so that women can rule our sex lives by their choices.  This confirms what I've observed over many years, that people whose long-term sexual relationships seem happiest are ones who appear to have recognized and accomodated that fundamental feature of our sexuality.