Why Are Men and Women Different?

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

Many scientists rely on elaborately complex and costly equipment to probe the mysteries confronting humankind. Not Melissa Hines. The UCLA behavioral scientist is hoping to solve one of life’s oldest riddles with a toybox full of police cars, Lincoln Logs and Barbie dolls. For the past two years, Hines and her colleagues have tried to determine the origins of gender differences by capturing on videotape the squeals of delight, furrows of concentration and myriad decisions that children from 2 1/2 to 8 make while playing. Although both sexes play with all the toys available in Hines’ laboratory, her work confirms what most parents (and more than a few aunts, uncles and nursery- school teachers) already know. As a group, the boys favor sports cars, fire trucks and Lincoln Logs, while the girls are drawn more often to dolls and kitchen toys.

But one batch of girls defies expectations and consistently prefers the boy toys. These youngsters have a rare genetic abnormality that caused them to produce elevated levels of testosterone, among other hormones, during their embryonic development. On average, they play with the same toys as the boys in the same ways and just as often. Could it be that the high levels of testosterone present in their bodies before birth have left a permanent imprint on their brains, affecting their later behavior? Or did their parents, knowing of their disorder, somehow subtly influence their choices? If the first explanation is true and biology determines the choice, Hines wonders, “Why would you evolve to want to play with a truck?”

Not so long ago, any career-minded researcher would have hesitated to ask such questions. During the feminist revolution of the 1970s, talk of inborn differences in the behavior of men and women was distinctly unfashionable, even taboo.

But biology has a funny way of confounding expectations. Rather than disappear, the evidence for innate sexual differences only began to mount.

Even professional skeptics have been converted. “When I was younger, I believed that 100% of sex differences were due to the environment,” says Jerre Levy, professor of psychology at the University of Chicago. Her own toddler toppled that utopian notion.

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