Humans aren't bacteria – we come in two sexes, and we're obsessed with differences between them, starting with: boy or girl? We often think that there are certain sex differences – one sex is better at expressing feelings, the other at reading maps. One is aggressive, the other nurturing. One is intelligent, the other isn't ready for equal pay. You see where this can lead. And has.

Nonetheless, statistically reliable sex differences do exist. One is that women are way underrepresented in the upper echelons of science; for example, only 5 percent of Nobel Prizes have been awarded to women, and mostly for literature. Thus, something interesting happened a few weeks ago when this year's Nobels were awarded – four of the 11 science prizes went to women, including UC San Francisco's Liz Blackburn.

That's great, pleasing, nice and splashy. But recently, in a quieter but more substantive way, another sex difference has gone down the tubes.

A remarkably consistent finding, starting with elementary school students, is that males are better at math than females. While the difference is minor when considering average math scores, there's a huge difference when it comes to math stars. For example, in 1983, for every girl scoring in the highest levels on the math SAT, there were 11 boys.

What explains this difference? A female friend once said, "How can we be good at math when men tell us that something 6 inches long is actually 12 inches long?" But there may be some other things happening. For example, during development, testosterone increases the size in males of a brain region involved in mathematical thinking, and giving adults testosterone enhances those math skills. Findings like these suggest that sex differences in math aptitude are embedded in the brain, in sex hormones that influence the brain and in the genes that specify those hormones.


In a study published last year in the prestigious journal Science, psychologist Janet Hyde at the University of Wisconsin examined math test scores from 7 million schoolchildren and, whoa, in the past decade, the sex difference has disappeared. What happened? The authors note that this period was the first time that girls chose to take as much elective math as boys – when girls are as interested in math as boys, they're suddenly as good at it.

Next, consider a paper in Science by Luigi Guiso and colleagues in Italy. They examined the relationship between math scores and the degree of sexual equality in 40 countries (using an index based on the degree of economic, educational and political gender equality; for the curious, Turkey scored worst, the United States was middling, and the Scandinavians were tops). And the more gender-equal a country, the smaller the sex difference in math scores. In Iceland, the most equal country, girls were better at math. Biology? – apparently not.

But what about the dearth of female math geniuses? That 11-to-1 ratio of boy-to-girl math whizzes in 1983 shriveled to 3-to-1 by the 1990s, and is 1-to-1 in gender-equal countries. The neurobiological effects of sex hormones didn't magically change over a decade; genetic change can't explain this shrinking ratio any more than explaining why shoulder pads on women's jackets were cool in 1983, but not by 1995. If the next Newton is male, it won't be because of his Y-chromosome.

The brain is constantly reshaped by environment. As we contemplate findings like these, it's worth appreciating how powerfully the brain is sculpted by society's values and beliefs.

Stanford University neurology professor Robert M. Sapolsky is the author of "A Primate's Memoir," among other works.


Source: San Francisco Chronicle –