Why the female brain is like a Swiss army knife

In this article:
Why men hate to ask for directions
Why women can find the socks
The bottom line on gender
Special Report: The Brain
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In fact, one of the biggest revolutions in the study of brain anatomy is the growing acknowledgment that few organs are as sexually dimorphic as the human brain.

Pioneering neuroendocrinologist Roger Gorski, Ph.D., a brain researcher at the UCLA School of Medicine, points to half a dozen proven differences between male and female brains. Differences between the brains of heterosexual and homosexual men have been tentatively identified, and there's even a demonstrable difference between the brains of gay men and male-to-female transsexuals.

All brains start out inherently female, the theory goes, but exposure to male hormones in the womb leads to differential development in boys. One sexual difference found in rats and humans alike is a structure called the SDN, or sexually dimorphic nucleus, a cluster of cells in the hypothalamus that's 2 1/2 times bigger in males than in females. In rats, the SDN plays a role in mating and territorial behavior, though its function in humans remains unknown. Gorski has shown that by giving a male rat fetus a substance that blocks male hormones, its SDN will remain as small as a female's. Conversely, dosing a female rate fetus with male hormones will cause her SDN to grow as large as a male's.

Another brain structure with a sex-based size discrepancy - this time, it's larger or thicker in women - is the corpus callosum, the bundle of nerves that link the right and left hemispheres like a biological computer cable. Two other connecting cables, the anterior commissure and the massa intermedia, are larger in women. Some researchers suspect that this more integrated linkage might explain "women's intuition," a kind of whole-brain processing.

In overall size, men's brains average 15 percent larger than women's - about two times the average difference in body size. Male supremacists, check your smugness. "Size in and of itself is not intelligence," says Lucia Jacobs, Ph.D., a psychologist and neuroscientist at the University of California at Berkeley. "You can't say a cow is smarter than a mouse. It doesn't scale like that."

Much more important is the number of neurons and their structural organization. "If I had to pick a brain, I think I'd take a female brain," says Jacobs. "It's symmetrical, multitasking and more resistant to stroke because language ability is stored in both hemispheres. The female brain is like a Swiss army knife - whereas males get stuck with one big blade."

Why men hate to ask for directions

Such good-natured gibes notwithstanding, Jacobs and fellow scientists now believe there may be good reason why men and women evolved these differences.

Consider two classic cognitive measures: spatial rotation tests, in which men on average show a clear advantage; and object/location memory tests, where women are likely to excel. Test yourself, click here.

An early clue about the male advantage came from comparing two species of hamster-like rodents, the meadow vole and the pine vole. In meadow voles, males are wanderlusting philanderers that roam great distances in search of mates. In pine voles, males are monogamous homebodies.

University of Pittsburgh anthropologist Steve Gaulin, Ph.D., captured voles and tested how fast they learned to negotiate mazes. It turned out that the philandering male meadow voles were quite adept at mazes. Male pine voles, and the females of both species, learned much more slowly.

Dissection found that a brain structure called the hippocampus was 11 percent bigger in male meadow voles compared with the females. No such sex difference was found in pine voles.

The hippocampus is a small, complicated structure beneath the cerebral cortex; it loosely resembles its Latin namesake, the sea horse. Researchers have studied the hippocampus intensively for years but can only guess that it helps create mental maps of places its owner has not yet seen.

Evolutionary biologists speculate that our human male ancestors, who needed to range across large distances in pursuit of game (and conceivably indulge in a little philandering), had a similar need for a powerful map maker. Eons of enjoying the independence derived from this internal map making may be a real reason so many modern guys hate to ask directions.

Why women can find the socks

Another male-female cliché may have physiological underpinnings: the notion that so many "helpless" men never find things at home and always ask their wives for help. It may sound preposterous that evolution would favor female brains that are adept at finding socks. But in antiquity, females needed to track their immediate environment for food and knew the location of every nut and berry.

Look at the differences in action in a recent study: Volunteers agreed to negotiate a large maze that contained specific landmarks, then find their way back to the starting point. Men, on average, made it back home much more quickly than women did. Later, when asked to describe the trip, women could cite landmarks in detail. For men, the whole maze was a blur.

The bottom line on gender

Neither the male nor the female brain is inherently superior. In antiquity, offspring lucky enough to have parents with all bases covered tended to out-survive and out-reproduce those whose parents' brain power was not so complementary.

In the modern world, such differences may become inconsequential. Learning specialists, for instance, have begun to devise strategies for translating spatial problems (at which men often excel) into verbal problems (at which women often excel) - and vice versa - making it easier for individuals of both sexes to master new skills. Hand-held calculators and computerized grammar checkers further reduce on-average gender disparities.

In a sense, technology is the great equalizer: Even Arnold Schwarzenegger is an ant compared with a woman in the cockpit of an F-16.

By Jim Thornton
Thornton received a 1998 National Magazine Award for health reporting.
Illustration Credit: PETER HOEY for USA WEEKEND