The Moral Animal: Why We Are, the Way We Are: The New Science of Evolutionary Psychology (8 page)

But there is one thing they can do. Often a Darwinian theory generates, in addition to the pseudopredictions that the theory was in fact designed to explain, additional predictions — real predictions, untested predictions, which can be used to further evaluate the theory. (Darwin elliptically outlined this method in 1838, at age twenty-nine — more than twenty years before
The Origin of Species
was published. He wrote in his notebook: "The line of argument pursued throughout my theory is to establish a point as a probability by induction, & to apply it as hypothesis to other points, & see whether it will solve them.")
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The theory of parental investment is a good example. For there are a few oddball species, as Williams noted in 1966, in which the male's investment in the offspring roughly matches, or even exceeds, the female's. If the theory of parental investment is right, these species should defy sex stereotypes.

Consider the spindly creatures known as pipefish. Here the male plays a role like a female kangaroo's: he takes the eggs into a pouch and plugs them into his bloodstream for nutrition. The female can thus start on another round of reproduction while the male is playing nurse. This may not mean that she can have many more offspring than he in the long run — after all, it took her a while to produce the eggs in the first place. Still, the parental investment isn't grossly imbalanced in the usual direction. And, predictably, female pipefish tend to take an active role in courtship, seeking out the males and initiating the mating ritual.
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Some birds, such as the phalarope (including the two species known as sea snipes), exhibit a similarly abnormal distribution of parental investment. The males sit on the eggs, leaving the females free to go get some wild oats sown. Again, we see the expected departure from stereotype. It is the phalarope females who are larger and more colorful — a sign that sexual selection is working in reverse, as females compete for males. One biologist observed that the females, in classically male fashion, "quarrel and display among themselves" while the males patiently incubate the eggs.
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If the truth be told, Williams knew that these species defy stereotype when he wrote in 1966. But subsequent investigation has confirmed his "prediction" more broadly. Extensive parental investment by males has been shown to have the expected consequences
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in other birds, in the Panamanian poison-arrow frog, in a water bug whose males cart fertilized eggs around on their backs, and in the (ironically named, it turns out) Mormon cricket. So far Williams's prediction has encountered no serious trouble.
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There is another major form of evolutionary evidence bearing on differences between men and women: our nearest relatives. The great apes — chimpanzees, pygmy chimps (also called bonobos), gorillas, and orangutans — are not, of course, our ancestors; all have evolved since their path diverged from ours. Still, those forks in the road have come between eight million years ago (for chimps and bonobos) and sixteen million years ago (for orangutans).
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That's not long, as these things go. (A reference point: The australopithecine, our presumed ancestor, whose skull was ape-sized but who walked upright, appeared between six and four million years ago, shortly after the chimpanzee off-ramp. Homo erectus — the species that had brains midway in size between ours and apes', and used them to discover fire — took shape around 1.5 million years ago.)
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The great apes' nearness to us on the evolutionary tree legitimizes a kind of detective game. It's possible — though hardly certain — that when a trait is shared by all of them and by us, the reason is common descent. In other words: the trait existed in our common, sixteen-million-year-old proto-ape ancestor, and has been in all our lineages ever since. The logic is roughly the same as tracking down four distant cousins, finding that they all have brown eyes, and inferring that at least one of their two common great-great-grandparents had brown eyes. It's far from being an airtight conclusion, but it has more credence than it had when you had seen only one of the cousins.
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Lots of traits are shared by us and the great apes. For many of the traits — five-fingered hands, say — pointing this out isn't worth the trouble; no one doubts the genetic basis of human hands anyway. But in the case of human mental traits whose genetic substratum is still debated — such as the differing sexual appetites of men and women — this inter-ape comparison can be useful. Besides, it's worth taking a minute to get acquainted with our nearest relatives. Who
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knows how much of our psyche we share by common descent with some or all of them?

Orangutan males are drifters. They wander in solitude, looking for females, who tend to be stationary, each in her own home range. A male may settle down long enough to monopolize one, two, or even more of these ranges, though vast monopolies are discouraged by the attendant need to fend off vast numbers of rivals. Once the mission is accomplished, and the resident female gives birth, the male is likely to disappear. He may return years later, when pregnancy is again possible.
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In the meantime, he doesn't bother to write.

For a gorilla male, the goal is to become leader of a pack comprising several adult females, their young offspring, and maybe a few young adult males. As dominant male, he will get sole sexual access to the females; the young males generally mind their manners (though a leader may, as he ages and his strength ebbs, share females with them).
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On the downside, the leader does have to confront any male interlopers, each of which aims to make off with one or more of his females and thus is in an assertive mood.

The life of the male chimpanzee is also combative. He strives to climb a male hierarchy that is long and fluid compared to a gorilla hierarchy. And, again, the dominant male — working tirelessly to protect his rank through assault, intimidation, and cunning — gets first dibs on any females, a prerogative he enforces with special vigor when they're ovulating.
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Pygmy chimps, or bonobos (they're actually a distinct species from chimpanzees), may be the most erotic of all primates. Their sex comes in many forms and often serves purposes other than reproduction. Periodic homosexual behavior, such as genital rubbings between females, seems to be a way of saying, "Let's be friends." Still, broadly speaking, the bonobos' sociosexual outline mirrors that of the common chimpanzees: a pronounced male hierarchy that helps determine access to females.
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Amid the great variety of social structure in these species, the basic theme of this chapter stands out, at least in minimal form: males seem very eager for sex and work hard to find it; females work less hard. This isn't to say the females don't like sex. They love it, and may initiate it. And, intriguingly, the females of the species most
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closely related to humans — chimpanzees and bonobos — seem particularly amenable to a wild sex life, including a variety of partners. Still, female apes don't do what male apes do: search high and low, risking life and limb, to find sex, and to find as much of it, with as many different partners, as possible; it has a way of finding them.

That female apes are, on balance, more reticent than male apes doesn't necessarily mean that they actively screen their prospective partners. To be sure, the partners get screened; those who dominate other males mate, while those who get dominated may not. This competition is exactly what Darwin had in mind in defining one of the two kinds of sexual selection, and these species (like our own) illustrate how it favors the evolution of big, mean males. But what about the other kind of sexual selection? Does the female participate in the screening, choosing the male that seems the most auspicious contributor to her project?

Female choice is notoriously hard to spot, and signs of its long-term effect are often ambiguous. Are males larger and stronger than females just because tougher males have bested their rivals and gotten to mate? Or, in addition, have females come to prefer tough males, since females with this genetically ingrained preference have had tougher and therefore more prolific sons, whose many daughters then inherited their grandmother's taste?

Notwithstanding such difficulties, it's fairly safe to say that in one sense or another, females are choosy in all the great ape species. A female gorilla, for example, though generally confined to sex with a single, dominant male, normally emigrates in the course of her lifetime. When an alien male approaches her pack, engaging its leader in mutual threats and maybe even a fight, she will, if sufficiently impressed, decide to follow him.
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In the case of chimps, the matter is more subtle. The dominant, or alpha, male can have any female he wants, but that's not necessarily because she prefers him; he shuts off alternatives by frightening other males. He can frighten her too, so that any spurning of low-ranking males may reflect only her fear. (Indeed, the spurning has been known
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to disappear when the alpha isn't looking.)
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But there is a wholly different kind of chimp mating — a sustained, private consortship that may be a prototype for human courtship. A male and female chimp will leave the community for days or even weeks. And although the female may be forcibly abducted if she resists an invitation, there are times when she successfully resists, and times when she chooses to go peacefully, even though nearby males would gladly aid her in any resistance.
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Actually, even going unpeacefully can involve a kind of choice. Female orangutans are a good example. They do often seem to exercise positive choice, favoring some males over others. But sometimes they resist a mating and are forcibly subdued and — insofar as this word can be applied to nonhumans — raped. There is evidence that the rapists, often adolescents, usually fail to impregnate.
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But suppose that they succeed with some regularity. Then a female, in sheerly Darwinian terms, is better off mating with a good rapist, a big, strong, sexually aggressive male; her male offspring will then be more likely to be big, strong, and sexually aggressive (assuming sexual aggressiveness varies at least in part because of genetic differences) — and therefore prolific. So female resistance should be favored by natural selection as a way to avoid having a son who is an inept rapist (assuming it doesn't bring injury to the female).

This isn't to say that a female primate, her protests notwithstanding, "really wants it," as human males have been known to assume. On the contrary, the more an orangutan "really wants it," the less she'll resist, and the less powerful a screening device her reticence will be. What natural selection "wants" and what any individual wants needn't be the same, and in this case they're somewhat at odds. The point is simply that, even when females demonstrate no clear preference for certain kinds of males, they may be, in practical terms, preferring a certain kind of male. And this de facto discretion may be de jure. It may be an adaptation, favored by natural selection precisely because it has this filtering effect.

In the broadest sense, the same logic could apply in any primate species. Once females in general begin putting up the slightest resistance, then a female that puts up a little extra resistance is exhibiting a valuable trait. For whatever it takes to penetrate resistance, the sons
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of strong resisters are more likely to have it than the sons of weak resisters. (This assumes, again, that the relative possession by different males of "whatever it takes" reflects underlying genetic differences.) Thus, in sheerly Darwinian terms, coyness becomes its own reward. And this is true regardless of whether the male's means of approach is physical or verbal.

A common reaction to the new Darwinian view of sex is that it makes perfect sense as an explanation for animal behavior — which is to say, for the behavior of nonhuman animals. People may chuckle appreciatively at a male turkey that tries to mate with a poor rendition of a female's head, but if you then point out that many a human male regularly gets aroused after looking at two-dimensional representations of a nude woman, they don't see the connection. After all, the man surely knows that it's only a photo he's looking at; his behavior may be pathetic, but it isn't comic.

And maybe it isn't. But if he "knows" it's a photo, why is he getting so excited? And why are women so seldom whipped up into an onanistic frenzy by pictures of men?

Resistance to lumping humans and turkeys under one set of Darwinian rules has its points. Yes, our behavior is under more subtle, presumably more "conscious," control than is turkey behavior. Men can decide not to get aroused by something — or, at least, can decide not to look at something they know will arouse them. Sometimes they even stick with those decisions. And although turkeys can make what look like comparable "choices" (a turkey hounded by a shotgun-wielding man may decide that now isn't the time for romance), it is plainly true that the complexity and subtlety of options available to a human are unrivaled in the animal kingdom. So too is the human's considered pursuit of very long-run goals.

It all feels very rational, and in some ways it is. But that doesn't mean it isn't in the service of Darwinian ends. To a layperson, it may seem natural that the evolution of reflective, self-conscious brains would liberate us from the base dictates of our evolutionary past. To an evolutionary biologist, what seems natural is roughly the opposite: that human brains evolved not to insulate us from the mandate to
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survive and reproduce, but to follow it more effectively, if more pliably; that as we evolve from a species whose males forcibly abduct females into a species whose males whisper sweet nothings, the whispering will be governed by the same logic as the abduction — it is a means of manipulating females to male ends, and its form serves this function. The basic emanations of natural selection are refracted from the older, inner parts of our brain all the way out to its freshest tissue. Indeed, the freshest tissue would never have appeared if it didn't toe natural selection's bottom line.