His brain, her brain
Anyone who's heard a group of men discuss the virtues of high-end stereo equipment will have little trouble believing that men's and women's brains work differently. That's also no surprise to scientists, who have spent the past two decades trying to figure out which aspects of cognition and behavior are determined by nature and which by nurture. The verdict: Female and male brains differ in both structure and function, and many of those variations start in the womb. It's no longer: "Is there a difference?" It's: "What do these differences mean?"
Male and female brains differ in how they're built, with some parts larger in men, others larger in women. The variation is most striking in overall size. Women's brains are about 10 percent smaller than men's, a fact that in centuries past provided ammunition for the argument that women were by nature mentally deficient. Yet, despite this difference, women do just as well as men on intelligence tests. Researchers at the University of California-Irvine say they have figured out one possible explanation: In January, they reported that men have more gray matter in the brain, and women have more white matter. Gray matter forms the brain's information-processing centers, and white matter serves as wiring to connect the processing centers. "Female brains might be more efficient," says Richard Haier, the psychologist who led the study. Women also tend to use their frontal lobes for intellectual performance, while the gray matter used by men is distributed throughout the brain. That has implications for treating diseases like stroke and Alzheimer's, Haier says; treatments could be targeted to protect or restore those critical regions.
Divergence. When it comes to putting brains to work, women and men have their own areas of expertise. Men do better than women at spatial tasks such as thinking about rotating or manipulating an object. They're also better at navigating along a route and at high-end mathematical reasoning; men have scored more perfect 800 scores on the math portion of the SAT than women have every year since 1964. Women excel at tests that measure word recall and at other tests of verbal memory. They're also better at remembering landmarks and where objects are located. It used to be thought that these differences in cognitive skills didn't emerge until puberty, but researchers have found the same differences in very young children.
The big question, of course, is whether the differences in his and her brains cause the variation in cognitive skills or whether society pushes women toward verbal, people-oriented tasks, and men toward quantitative fields like engineering. Few women in science have forgotten the infamous Teen Talk Barbie of 1992, which chirped, "Math is hard!" And although the number of women in the sciences has increased steadily over the past 30 years--women now compose the majority in medical schools and graduate programs in biology--they are still underrepresented in math, engineering, and physics.
In 1980, psychologists Julian Stanley and Camilla Benbow ignited a firestorm when they proposed that gifted boys did better at math than gifted girls because of a "math gene." The nature vs. nurture debate continues 25 years later, but it is becoming more pragmatic as researchers use MRI s and other brain-imaging tools that show differences in male and female brains even when performance is identical. "In the early '80s, we were worried that sex differences in the brain would be used against us as women," says Jill Becker, a psychologist at the University of Michigan. " We're all more comfortable with diversity these days, and we've come to accept that there are many different ways of solving a problem. No two brains are the same." -Nancy Shute
This story appears in the March 7, 2005 print edition of U.S. News & World Report.