Sizing Up The Sexes

Scientists are discovering that gender differences have as much to do with the biology of the brain as with the way we are raised

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First, Ojemann tested his patients' verbal intelligence using a written exam. Then, during neurosurgery -- which was performed under a local anesthetic -- he asked them to name aloud a series of objects found in a steady stream of black-and-white photos. Periodically, he touched different parts of the brain with an electrode that temporarily blocked the activity of that region. (This does not hurt because the brain has no sense of pain.) By noting when his patients made mistakes, the surgeon was able to determine which sites were essential to naming.

Several complex sexual differences emerged. Men with lower verbal IQs were more likely to have their language skills located toward the back of the brain. In a number of women, regardless of IQ, the naming ability was restricted to the frontal lobe. This disparity could help explain why strokes that affect the rear of the brain seem to be more devastating to men than to women.

Intriguingly, the sexual differences are far less significant in people with higher verbal IQs. Their language skills developed in a more intermediate part of the brain. And yet, no two patterns were ever identical. "That to me is the most important finding," Ojemann says. "Instead of these sites being laid down more or less the same in everyone, they're laid down in subtly different places." Language is scattered randomly across these cerebral centers, he hypothesizes, because the skills evolved so recently.

What no one knows for sure is just how hardwired the brain is. How far and at what stage can the brain's extraordinary flexibility be pushed? Several studies suggest that the junior high years are key. Girls show the same aptitudes for math as boys until about the seventh grade, when more and more girls develop math phobia. Coincidentally, that is the age at which boys start to shine and catch up to girls in reading.

By one account, the gap between men and women for at least some mental skills has actually started to shrink. By looking at 25 years' worth of data from academic tests, Janet Hyde, professor of psychology and women's studies at the University of Wisconsin at Madison, discovered that overall gender differences for verbal and mathematical skills dramatically decreased after 1974. One possible explanation, Hyde notes, is that "Americans have changed their socialization and educational patterns over the past few decades. They are treating males and females with greater similarity."

Even so, women still have not caught up with men on the mental-rotation test. Fascinated by the persistence of that gap, psychologists Irwin Silverman and Marion Eals of York University in Ontario wondered if there were any spatial tasks at which women outperformed men. Looking at it from the point of view of human evolution, Silverman and Eals reasoned that while men may have developed strong spatial skills in response to evolutionary pressures to be successful hunters, women would have needed other types of visual skills to excel as gatherers and foragers of food.

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