It's a stereotype, but in many cases, it's true: On personality tests, women tend to score as being more nurturing, emotionally responsive, cooperative and cautious than men; men, on average, are more competitive, assertive, reckless and, as the New York Times puts it, "emotionally flat." As John Tierney explains in a fascinating article on gender differences, these biases show up in childhood and never go away.

As anyone who pays attention to such things knows, there's a name for the long-standing debate about where these differences come from: Nature versus nurture. But now, the Times reports, new research is showing that both theories may be wrong -- or at least have different effects from what you might expect. An analysis of personality tests taken by men and women in more than 60 countries around the world shows that the size of the gender gap varies among cultures (bad for the "nature" adherents). And unfortunately for the "nurturers" who believe that if only societies were more equal, the differences between the sexes would disappear, it appears that the more traditional the culture (think India or Zimbabwe), the smaller the differences are, personality-wise, between men and women. As Tierney puts it, "The more Venus and Mars have equal rights and similar jobs, the more their personalities seem to diverge."

That's so counterintuitive that there must be a problem with the data, right? Maybe not: David Schmitt, a psychologist at Bradley University in Illinois and the director of the International Sex Description Project (that must be a fun one for cocktail parties), looked at data from 40,000 men and women on six continents and concluded that "as wealthy modern societies level external barriers between women and men, some ancient internal differences are being revived." Translation: When people don't have to worry as much about basic survival (as they do in agricultural societies and poorer countries), the differences between the sexes become more pronounced.

The article discusses a couple of arguments for why this might be (as well as counterarguments, such as the idea that people in different cultures might interpret personality test questions differently) -- including the idea that in animals, "environmental stress tends to disproportionately affect the larger sex and mute costly secondary sexual characteristics (like male birds' displays of plumage)." Wait -- so could it be that men in poor societies, struggling to survive, might be pressured into displaying the unattractive traits of being nurturing and emotionally responsive instead of allowing their sexy "emotional flatness" to shine? Sign me up for a Zimbabwe vacation!

More seriously, though, here's how Schmitt explains one theory, as described by the Times:

"Humanity's jaunt into monotheism, agriculturally based economies and the monopolization of power and resources by a few men was 'unnatural' in many ways," Dr. Schmitt says, alluding to evidence that hunter-gatherers were relatively egalitarian. "In some ways modern progressive cultures are returning us psychologically to our hunter-gatherer roots," he argues. “That means high sociopolitical gender equality over all, but with men and women expressing predisposed interests in different domains. Removing the stresses of traditional agricultural societies could allow men's, and to a lesser extent women's, more 'natural' personality traits to emerge."

Thoughts?