Mars & Venus

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.

The biggest changes recorded by the researchers involve the personalities of men, not women. Men in traditional agricultural societies and poorer countries seem more cautious and anxious, less assertive and less competitive than men in the most progressive and rich countries of Europe and North America.

To explain these differences, Dr. Schmitt and his collaborators from Austria and Estonia point to the hardships of life in poorer countries. They note that in some other species, environmental stress tends to disproportionately affect the larger sex and mute costly secondary sexual characteristics (like male birds’ displays of plumage). And, they say, there are examples of stress muting biological sex differences in humans. For instance, the average disparity in height between men and women isn’t as pronounced in poor countries as it is in rich countries, because boys’ growth is disproportionately stunted by stresses like malnutrition and disease.

Personality is more complicated than height, of course, and Dr. Schmitt suggests it’s affected by not just the physical but also the social stresses in traditional agricultural societies. These villagers have had to adapt their personalities to rules, hierarchies and gender roles more constraining than those in modern Western countries — or in clans of hunter-gatherers.

“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.”

Some critics of this hypothesis question whether the international variations in personality have more to do with the way people in different cultures interpret questions on personality tests. (For more on this debate, go to www.nytimes.com/tierneylab.) The critics would like to see more direct measures of personality traits, and so would Dr. Schmitt. But he notes that there’s already an intriguing trend reported for one trait — competitiveness — based on direct measures of male and female runners.

Competitive running makes a good case study because, to mix athletic metaphors, it has offered a level playing field to women the past two decades in the United States. Similar numbers of males and females run on high school and college teams and in road races. Female runners have been competing for equal shares of prize money and receiving nearly 50 percent more scholarship aid from Division I colleges than their male counterparts, according to the N.C.A.A.

But these social changes have not shrunk a gender gap among runners analyzed by Robert Deaner, a psychologist at Grand Valley State University in Michigan, who classifies runners as relatively fast if they keep close to the pace of the world’s best runners of their own sex. When Dr. Deaner looks at, say, the top 40 finishers of each sex in a race, he typically finds two to four times as many relatively fast male runners as relatively fast female runners.

This large gender gap has persisted for two decades in all kinds of races — high school and college meets, elite and nonelite road races — and it jibes with other studies reporting that male runners train harder and are more motivated by competition, Dr. Deaner says. This enduring “sex difference in competitiveness,” he concludes, “must be considered a genuine failure for the sociocultural conditions hypothesis” that the personality gap will shrink as new roles open for women.

If he and Dr. Schmitt are right, then men and women shouldn’t expect to understand each other much better anytime soon. Things could get confusing if the personality gap widens further as the sexes become equal. But then, maybe it was that allure of the mysterious other that kept Mars and Venus together so long on the savanna.