Why Do We Rape, Kill and Sleep Around?

On that point, the evidence instead suggests that both sexes prefer mates around their own age, adjusted for the fact that men mature later than women. If the male mind were adapted to prefer the most fertile women, then AARP-eligible men should marry 23-year-olds, which—Anna Nicole Smith and J. Howard Marshall notwithstanding—they do not, instead preferring women well past their peak fertility. And, interestingly, when Miller focuses on the science rather than tries to sell books, he allows that "human mate choice is much more than men just liking youth and beauty, and women liking status and wealth," as he told me by e-mail.

Yet evo psych remains hugely popular in the media and on college campuses, for obvious reasons. It addresses "these very sexy topics," says Hill. "It's all about sex and violence," and has what he calls "an obsession with Pleistocene just-so stories." And few people—few scientists—know about the empirical data and theoretical arguments that undercut it. "Most scientists are too busy to read studies outside their own narrow field," he says.

Far from ceding anything, evolutionary psychologists have moved the battle from science, where they are on shaky ground, to ideology, where bluster and name-calling can be quite successful. UNM's Miller, for instance, complains that critics "have convinced a substantial portion of the educated public that evolutionary psychology is a pernicious right-wing conspiracy," and complains that believing in evolutionary psychology is seen "as an indicator of conservatism, disagreeableness and selfishness." That, sadly, is how much too much of the debate has gone. "Critics have been told that they're just Marxists motivated by a hatred of evolutionary psychology," says Buller. "That's one reason I'm not following the field anymore: the way science is being conducted is more like a political campaign."

Where, then, does the fall of evolutionary psychology leave the idea of human nature? Behavioral ecology replaces it with "it depends"—that is, the core of human nature is variability and flexibility, the capacity to mold behavior to the social and physical demands of the environment. As Buller says, human variation is not noise in the system; it is the system. To be sure, traits such as symbolic language, culture, tool use, emotions and emotional expression do indeed seem to be human universals. It's the behaviors that capture the public imagination—promiscuous men and monogamous women, stepchild-killing men and the like—that turn out not to be. And for a final nail in the coffin, geneticists have discovered that human genes evolve much more quickly than anyone imagined when evolutionary psychology was invented, when everyone assumed that "modern" humans had DNA almost identical to that of people 50,000 years ago. Some genes seem to be only 10,000 years old, and some may be even younger.

That has caught the attention of even the most ardent proponents of evo psych, because when the environment is changing rapidly—as when agriculture was invented or city-states arose—is also when natural selection produces the most dramatic changes in a gene pool. Yet most of the field's leaders, admits UNM's Miller, "have not kept up with the last decade's astounding progress in human evolutionary genetics." The discovery of genes as young as agriculture and city-states, rather than as old as cavemen, means "we have to rethink to foundational assumptions" of evo psych, says Miller, starting with the claim that there are human universals and that they are the result of a Stone Age brain. Evolution indeed sculpted the human brain. But it worked in malleable plastic, not stone, bequeathing us flexible minds that can take stock of the world and adapt to it.

With Jeneen Interlandi

© 2009