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The Segregation Of The Senses
So how do we explain why, in study after study, boys and men are still on average better at rotating 3-D objects in their minds? As for girls and women, how do we explain why they tend to have better verbal skills and social sensitivities?
The most surprising differences may be outside the brain. "If you have a man and a woman looking at the same landscape, they see totally different things," asserts Leonard Sax, a physician and psychologist whose book Why Gender Matters came out last month.
"Women can see colors and textures that men cannot see. They hear things men cannot hear, and they smell things men cannot smell." Since the eyes, ears and nose are portals to the brain, they directly affect brain development from birth on.
In rats, for example, we know that the male retina has more cells designed to detect motion. In females, the retina has more cells built to gather information on color and texture. If the same is true in humans, as Sax suspects, that may explain why, in an experiment in England four years ago, newborn boys were much more likely than girls to stare at a mobile turning above their cribs. It may also help explain why boys prefer to play with moving toys like trucks while girls favor richly textured dolls and tend to draw with a wider range of colors, Sax says.
Likewise, women's ears are more sensitive to some noises. Baby girls hear certain ranges of sound better. And the divergence gets even bigger in adults. As for smell, a study published in the journal Nature Neuroscience in 2002 showed that women of childbearing age were many times more sensitive than men to several smells upon repeated exposure. (Another study has found that heterosexual women have the most sensitive smell and homosexual men have the least.) Rest assured, Sax says: none of that means women are, overall, better than men at perception. It just means the species is internally diverse, making it more likely to survive. "The female will remember the color and texture of a particular plant and be able to warn people if it's poisonous. A man looking at the same thing will be more alert to what is moving in the periphery," he says. "Which is better? You need both."
Never Underestimate The Brain
Until recently, there have been two groups of people: those who argue sex differences are innate and should be embraced and those who insist that they are learned and should be eliminated by changing the environment. Sax is one of the few in the middleconvinced that boys and girls are innately different and that we must change the environment so differences don't become limitations.
At a restaurant near his practice in Montgomery County, Md., Sax spreads out dozens of papers and meticulously makes his case. He is a fanatic, but a smart, patient one. In the early 1990s, he says, he grew alarmed by the "parade" of parents coming into his office wondering whether their sons had attention-deficit/hyperactivity disorder. Sax evaluated them and found that, indeed, the boys were not paying attention in school. But the more he studied brain differences, the more he became convinced that the problem was with the schools. Sometimes the solution was simple: some of the boys didn't hear as well as the girls and so needed to be moved into the front row. Other times, the solution was more complex. Eventually, Sax concluded that very young boys and girls would be better off in separate classrooms altogether.
"[Previously], as far as I was concerned, single-sex education was an old-fashioned leftover. I thought of boys wearing suits and talking with British accents," he says. But coed schools do more harm than good, he decided, when they teach boys and girls as if their brains mature at the same time. "If you ask a child to do something not developmentally appropriate for him, he will, No. 1, fail. No. 2, he will develop an aversion to the subject," he says. "By age 12, you will have girls who don't like science and boys who don't like reading." And they won't ever go back, he says. "The reason women are underrepresented in computer science and engineering is not because they can't do it. It's because of the way they're taught." So far, studies about girls' and boys' achievements in same-sex grammar schools are inconclusive. But if it turns out that targeting sex differences through education is helpful, there are certainly many ways to carry it out. Says Giedd: "The ability for change is phenomenal. That's what the brain does best." A small but charming 2004 study published in Nature found that people who learned how to juggle increased the gray matter in their brains in certain locations. When they stopped juggling, the new gray matter vanished.