In the New York Times, John Tierney reports:

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.

For my upcoming review of the remake of "The Women" with Meg Ryan, Annette Bening and the traditional all-female cast, I rented the 1939 George Cukor-directed original (based on the play by Clare Booth Luce), which is so good that my wife watched it three times over the weekend. It's the story of Park Avenue society ladies who can afford to indulge in every rococo frill of femininity. When all the ladies who lunch end up at a dude ranch in Reno for six weeks so they can qualify as Nevada residents and get quick divorces, their cook is a tough old cowgirl (played by Marjorie Main, who went on to star in the lucrative "Ma and Pa Kettle" comedies about a clan of hicks) who thinks the ultrafeminine New York women are silly and spoiled.

Ma and Pa Kettle both got a heap of farm chores to do, and don't have time, energy, or money to waste on, say, tiny purse dogs or playing Grand Theft Auto, so they might be more similar in important ways than a wealthy couple.

”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.”

Fortunately, there is some objective data on ... track and field! (And you were looking forward to a 3 year and 11 month respite until the next Olympics.)

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 Colgate University, 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.