When men and women take personality tests, some of the old Mars-Venus stereotypes keep reappearing. On average, women are more cooperative, nurturing, cautious and emotionally responsive. Men tend to be more competitive, assertive, reckless and emotionally flat. Clear differences appear in early childhood and never disappear.

What’s not clear is the origin of these differences. Evolutionary psychologists contend that these are innate traits inherited from ancient hunters and gatherers. Another school of psychologists asserts that both sexes’ personalities have been shaped by traditional social roles, and that personality differences will shrink as women spend less time nurturing children and more time in jobs outside the home.

To test these hypotheses, a series of research teams have repeatedly analyzed personality tests taken by men and women in more than 60 countries around the world. For evolutionary psychologists, the bad news is that the size of the gender gap in personality varies among cultures. For social-role psychologists, the bad news is that the variation is going in the wrong direction. It looks as if personality differences between men and women are smaller in traditional cultures like India’s or Zimbabwe’s than in the Netherlands or the United States. A husband and a stay-at-home wife in a patriarchal Botswanan clan seem to be more alike than a working couple in Denmark or France. The more Venus and Mars have equal rights and similar jobs, the more their personalities seem to diverge.

These findings are so counterintuitive that some researchers have argued they must be because of cross-cultural problems with the personality tests. But after crunching new data from 40,000 men and women on six continents, David P. Schmitt and his colleagues conclude that the trends are real. Dr. Schmitt, a psychologist at Bradley University in Illinois and the director of the International Sexuality Description Project, suggests that as wealthy modern societies level external barriers between women and men, some ancient internal differences are being revived.