Baron-Cohen was "bowled over" by the results. The more testosterone the children had been exposed to in the womb, the less able they were to make eye contact at 1 year of age. "Who would have thought that a behavior like eye contact, which is so intrinsically social, could be in part shaped by a biological factor?" he asks. What's more, the testosterone level during fetal life also influenced language skills. The higher the prenatal testosterone level, the smaller a child's vocabulary at 18 months and again at 24 months.

Lack of eye contact and poor language aptitude are early hallmarks of autism. "Being strongly attracted to systems, together with a lack of empathy, may be the core characteristics of individuals on the autistic spectrum," says Baron-Cohen. "Maybe testosterone does more than affect spatial ability and language. Maybe it also affects social ability." And perhaps autism represents an "extreme form" of the male brain.

Depression: Pink -- and Blue, Blue, Blue

This year, 19 million Americans will suffer a serious depression. Two out of three will be female. Over the course of their lives, 21.3 percent of women and 12.7 percent of men experience at least one bout of major depression.

The female preponderance in depression is virtually universal. And it's specific to unipolar depression. Males and females suffer equally from bipolar, or manic, depression. However, once depression occurs, the clinical course is identical in men and women.

The gender difference in susceptibility to depression emerges at 13. Before that age, boys, if anything, are a bit more likely than girls to be depressed. The gender difference seems to wind down four decades later, making depression mostly a disorder of women in the child-bearing years.

As director of the Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University, Kenneth S. Kendler, M.D., presides over "the best natural experiment that God has given us to study gender differences" -- thousands of pairs of opposite-sex twins. He finds a significant difference between men and women in their response to low levels of adversity. He says, "Women have the capacity to be precipitated into depressive episodes at lower levels of stress."

Adding injury to insult, women's bodies respond to stress differently than do men's. They pour out higher levels of stress hormones and fail to shut off production readily. The female sex hormone progesterone blocks the normal ability of the stress hormone system to turn itself off. Sustained exposure to stress hormones kills brain cells, especially in the hippocampus, which is crucial to memory.

It's bad enough that females are set up biologically to internally amplify their negative life experiences. They are prone to it psychologically as well, finds University of Michigan psychologist Susan Nolen-Hoeksema, Ph.D.

Women ruminate over upsetting situations, going over and over negative thoughts and feelings, especially if they have to do with relationships. Too often they get caught in downward spirals of hopelessness and despair.

It's entirely possible that women are biologically primed to be highly sensitive to relationships. Eons ago it might have helped alert them to the possibility of abandonment while they were busy raising the children. Today, however, there's a clear downside. Ruminators are unpleasant to be around, with their oversize need for reassurance. Of course, men have their own ways of inadvertently fending off people. As pronounced as the female tilt to depression is the male excess of alcoholism, drug abuse and antisocial behaviors.


The Incredible Shrinking Double Standard

Nothing unites men and women better than sex. Yet nothing divides us more either. Males and females differ most in mating psychology because our minds are shaped by and for our reproductive mandates. That sets up men for sex on the side and a more casual attitude toward it.

Twenty-five percent of wives and 44 percent of husbands have had extramarital intercourse, reports Baltimore psychologist Shirley Glass, Ph.D. Traditionally for men, love is one thing and sex is...well, sex.

In what may be a shift of epic proportions, sexual infidelity is mutating before our very eyes. Increasingly, men as well as women are forming deep emotional attachments before they even slip into an extramarital bed together. It often happens as they work long hours together in the office.

"The sex differences in infidelity are disappearing," says Glass, the doyenne of infidelity research. "In my original 1980 study, there was a high proportion of men who had intercourse with almost no emotional involvement at all -- nonrelational sex. Today, more men are getting emotionally involved."

One consequence of the growing parity in affairs is greater devastation of the betrayed spouse. The old-style strictly sexual affair never impacted men's marital satisfaction. "You could be in a good marriage and still cheat," reports Glass.

Liaisons born of the new infidelity are much more disruptive -- much more likely to end in divorce. "You can move away from just a sexual relationship but it's very difficult to break an attachment," says Rutgers University anthropologist Helen Fisher, Ph.D. "The betrayed partner can probably provide more exciting sex but not a different kind of friendship."

It's not that today's adulterers start out unhappy or looking for love. Says Glass: "The work relationship becomes so rich and the stuff at home is pressurized and child-centered. People get involved insidiously without planning to betray."

Any way it happens, the combined sexual-emotional affair delivers a fatal blow not just to marriages but to the traditional male code. "The double standard for adultery is disappearing," Fisher emphasizes. "It's been around for 5,000 years and it's changing in our lifetime. It's quite striking. Men used to feel that they had the right. They don't feel that anymore."




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