The Moral Animal: Why We Are, the Way We Are: The New Science of Evolutionary Psychology (13 page)

The dynamics of sexual treachery are different for humans than for bluegill sunfish, in part because of the mammalian penchant for
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internal fertilization. But Richard Dawkins has shown, with an abstract analysis applicable to our species, that Maynard Smith's logic can, in principle, fit us too. In other words: one can imagine a situation in which neither coy nor fast women, and neither cads nor dads, have a monopoly on the ideal strategy. Rather, the success of each strategy varies with the prevalence of the three other strategies, and the population tends toward equilibrium. For example, with one set of assumptions, Dawkins found that five-sixths of the females would be coy, and five-eighths of the males would be faithful.
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Now, having comprehended this fact, you are advised to forget it. Don't just forget the fractions themselves, which, obviously, grow out of arbitrary assumptions within a highly artificial model. Forget the whole idea that each individual would be firmly bound to one strategy or the other.

As Maynard Smith and Dawkins have noted, evolution equilibrates to an equally stable state if you assume that the magic proportions are found within individuals — that is, if each female is coy on five-sixths of her mating opportunities, and each male is coy on five-eighths of his. And that's true even if the fractions are randomly realized — if each person just rolls dice on each encounter to decide what to do. Imagine how much more effective it is for the person to ponder each situation (consciously or unconsciously) and make an informed guess as to which strategy is more propitious under the circumstances.

Or imagine a different kind of flexibility: a developmental program that, during childhood, assesses the local social environment and then, by adulthood, inclines the person toward the strategy more likely to pay off. To put this in bluegill terms: imagine a male that during its early years checks out the local environment, calculates the prevalence of exploitable, upstanding males, and then decides — or, at least, "decides" — whether to become a drifter. This plasticity should eventually dominate the population, pushing the two more rigid strategies into oblivion.

The moral of the story is that limberness, given the opportunity, usually wins out over stiffness. In fact, limberness seems to have won a partial victory even in the bluegill sunfish, which isn't exactly known
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for its highly developed cerebral cortex. Though some genes incline a male bluegill to one strategy, and others to the other, the inclination isn't complete; the male absorbs local data before "deciding" which strategy to adopt.
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Obviously, when you move from fish to us, the likely extent of flexibility grows. We have huge brains whose whole reason for being is deft adjustment to variable conditions. Given the many things about a person's social environment that can alter the value of being a Madonna versus a whore, a cad versus a dad — including the way other people react to the person's particular assets and liabilities — natural selection would be uncharacteristically obtuse not to favor genes that build brains sensitive to these things.

So too in many other realms. The value of being a given "type" of person — cooperative, say, or stingy — has depended, during evolution, on things that vary from time to time, place to place, person to person. Genes that irrevocably committed our ancestors to one personality type should in theory have lost out to genes that let the personality solidify gracefully.

This is not a matter of consensus. There are in the literature a few articles with titles like "The Evolution of the 'Con Artist.' "
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And, to return to the realm of Madonnas and whores, there is a theory that some women are innately inclined to pursue a "sexy son" strategy: they mate promiscuously with sexually attractive men (handsome, brainy, brawny, and so on), risking the high male parental investment they might extract if more Madonnaish but gaining the likelihood that any sons will be, like their fathers, attractive and therefore prolific. Such theories are interesting, but they all face the same obstacle: with con artists as with promiscuous women, however effective the strategy, it is even more effective when flexible — when it can be abandoned amid signs of likely failure.
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And the human brain is a pretty flexible thing.

To stress this flexibility isn't to say that all people are born psychologically identical, that all differences in personality emerge from environment. There plainly are important genetic differences for such traits as nervousness and extroversion. The "heritability" of these traits is around .4; that is, about 40 percent of individual differences in these traits (within the particular populations geneticists have studied)
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can be explained by genetic differences. (By comparison, the heritability of height is around .9; about 10 percent of the difference in height among individuals is due to nutritional and other environmental differences.) The question is why the undoubtedly important genetic variation in personality exists. Do different degrees of genetic disposition toward extroversion represent different personality "types," the products of a very elaborate process of frequency-dependent selection? (Though frequency dependence is classically analyzed in terms of two or three distinct strategies, it could also yield a more finely graded array.) Or are the differing genetic dispositions just "noise" — some incidental by-product of evolution, not specifically favored by natural selection? No one knows, and evolutionary psychologists differ in their suspicions.
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What they agree on is that a big part of the story of personality differences is the evolution of malleability, of "developmental plasticity."

This emphasis on psychological development doesn't leave us back where social scientists were twenty-five years ago, attributing everything they saw to often unspecified "environmental forces." A primary — perhaps the primary — promise of evolutionary psychology is to help specify the forces, to generate good theories of personality development. In other words: evolutionary psychology can help us see not only the "knobs" of human nature, but also how the knobs are tuned. It not only shows us that (and why) men in all cultures are quite attracted to sexual variety, but can suggest what circumstances make some men more obsessed with it than others; it not only shows us that (and why) women in all cultures are more sexually reserved, but promises to help us figure out how some women come to defy this stereotype.

A good example lies in Robert Trivers's 1972 paper on parental investment. Trivers noted two patterns that social scientists had already uncovered: (1) the more attractive an adolescent girl, the more likely she is to "marry up" — marry a man of higher socioeconomic status; and (2) the more sexually active an adolescent girl, the less likely she is to marry up.

To begin with, these two patterns make Darwinian sense independently. A wealthy, high-status male often has a broad range of aspiring wives to choose from. So he tends to choose a good-looking
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woman who is also relatively Madonnaish. Trivers took the analysis further. Is it possible, he asked, "that females adjust their reproductive strategies in adolescence to their own assets"?
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In other words, maybe adolescent girls who get early social feedback affirming their beauty make the most of it, becoming sexually reserved and thus encouraging long-term investment by high-status males who are looking for pretty Madonnas. Less attractive women, with less chance to hit the jackpot via sexual reserve, become more promiscuous, extracting small chunks of resources from a series of males. Though this promiscuity may somewhat lower their values as wives, it wouldn't, in the ancestral environment, have doomed their chances of finding a husband. In the average hunter-gatherer society, almost any fertile woman can find a husband, even if he's far from ideal, or she has to share him with another woman.

The Trivers scenario doesn't imply a conscious decision by attractive women to guard their jewels (though that may play a role, and, what's more, parents may be genetically inclined to encourage a daughter's sexual reserve with special force when she is pretty). By the same token, we aren't necessarily talking about unattractive women who "realize" they can't be choosy and start having sex on less than ideal Darwinian terms. The mechanism at work might well be subconscious, a gradual molding of sexual strategy — read: "moral values" — by adolescent experience.

Theories like this one matter. There has been much talk about the problem of unwed motherhood among teenagers, especially poor teenagers. But no one really knows how sexual habits get shaped, or how firmly fixed they then are. There is much talk about boosting "self-esteem," but little understanding of what self-esteem is, what it's for, or what it does.

Evolutionary psychology can't yet confidently provide the missing basis for these discussions. But the problem isn't a shortage of plausible theories; it's a shortage of studies to test the theories. The Trivers theory has sat in limbo for two decades. In 1992, one psychologist did find what the theory predicts — a correlation between
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a woman's self-perception and her sexual habits: the less attractive she thinks she is, the more sex partners she has had. But another scholar didn't find the predicted correlation — and, more to the point, neither study was conducted specifically to test Trivers's theory, of which both scholars were unaware.
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For now, this is the state of evolutionary psychology: so much fertile terrain, so few farmers.

Eventually, the main drift of Trivers's theory, if not the theory itself, will likely be vindicated. That is: women's sexual strategies probably depend on the likely (genetic) profitability of each strategy, given prevailing circumstances. But those circumstances go beyond what Trivers stressed — a particular woman's desirability. Another factor is the general availability of male parental investment. This factor surely fluctuated in the ancestral environment. For example, a village that had just invaded a neighboring village might have a suddenly elevated ratio of women to men — not just because of male casualties, but because victorious warriors commonly kill or vanquish enemy men and keep their women.
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Overnight, a young woman's prospects for receiving a man's undivided investment could thus plummet. Famine, or sudden abundance, might also alter investment patterns. Given these currents of change, any genes that helped women navigate them would, in theory, have flourished.

There is tentative evidence that they did. According to a study by the anthropologist Elizabeth Cashdan, women who perceive men in general as pursuing no-obligation sex are more likely to wear provocative clothes and have sex often than women who see men as generally willing to invest in offspring.
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Though some of these women may be conscious of the connection between local conditions and their lifestyle, that isn't necessary. Women surrounded by men who are unwilling or unable to serve as devoted fathers may simply feel a deepened attraction to sex without commitment — feel, in other words, a relaxation of "moral" constraint. And perhaps if market conditions suddenly improve — if the male to female ratio rises, or if men for some other reason shift toward a high-investment strategy — women's sexual attractions, and moral sensibilities, shift accordingly.

All of this is necessarily speculative at this early stage in evolutionary psychology's growth. But already we can see the sort of light that will increasingly be shed. For example, "self-esteem" almost
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certainly isn't the same, either in its sources or in its effects, for boys and girls. For teenage girls, feedback reflecting great beauty may, as Trivers suggested, bring high self-esteem, which in turn encourages sexual restraint. For boys, extremely high self-esteem could well have the opposite effect: it may lead them to seek with particular intensity the short-term sexual conquests that are, in fact, more open to a good-looking, high-status male. In many high schools, a handsome, star athlete is referred to, only half-jokingly, as a "stud." And, for those who insist on scientific verification of the obvious: good-looking men do have more sex partners than the average man.
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(Women report putting more emphasis on a sex partner's looks when they don't expect the relationship to last; they are apparently willing, unconsciously, to trade off parental investment for good genes.)
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Once a high-self-esteem male is married, he may not be notable for his devotion. Presumably his various assets still make philandering a viable lifestyle, even if it's now covert. (And you never know when an outside escapade will take on a life of its own, and lead to desertion.) Men with more moderate self-esteem may make more committed, if otherwise less desirable, husbands. With fewer chances at extramarital dalliance, and perhaps more insecurity about their own mate's fidelity, they may focus their energy and attention toward family. Meanwhile, men with extremely low self-esteem, given continued frustration with women, may eventually resort to rape. There is ongoing debate within evolutionary psychology over whether rape is an adaptation, a designed strategy that any boy might grow up to adopt, given sufficiently discouraging feedback from his social environment. Certainly rape surfaces in a wide variety of cultures, and often under the expected circumstances: when men have had trouble finding attractive women by legitimate means. One (non-Darwinian) study found the typical rapist to possess "deep-seated doubts about his adequacy and competency as a person. He lacks a sense of confidence in himself as a man in both sexual and nonsexual areas."
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A second sort of light shed by the new Darwinian paradigm may illuminate links between poverty and sexual morality. Women living in an environment where few men have the ability and/or desire to support a family might naturally grow amenable to sex without commitment. (Often in history — including Victorian England — women
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in the "lower classes" have had a reputation for loose morals.)
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It is too soon to assert this confidently, or to infer that inner-city sexual mores would change markedly if income levels did. But it is noteworthy, at least, that evolutionary psychology, with its emphasis on the role of environment, may wind up highlighting the social costs of poverty, and thus at times lend strength to liberal policy prescriptions, defying old stereotypes of Darwinism as right-wing.