Harvard University president Lawrence Summers has suffered acrimonious condemnation, and may have jeopardized his job, for suggesting that the underrepresentation of women in engineering and some scientific fields may be due in part to inherent differences in the intellectual abilities of the sexes.
But Summers could be right.
Some scholars who are in the know about the differences between mens' and womens' brains believe his remarks have merit.
"Among people who do the research, it's not so controversial. There are lots and lots of studies that show that men's and women's brains are different," said Richard J. Haier, a professor of psychology in the pediatrics department of the University of California Los Angeles medical school.
Academia has been bitterly divided in recent years by the nature vs. nurture debate, and the Harvard president's comments last month at a National Bureau of Economic Research symposium squarely address aspects of that dispute that are so controversial the opposing sides almost never discuss them.
On one side are those who believe the sexes are equal enough in their intellectual abilities that any biological difference between them is vastly outweighed by social pressures and discrimination that discourage girls and women from pursuing science and engineering.
"When people hear 'biology' they think there's nothing you can do about it," said Joshua Aronson, a professor of applied psychology at New York University. "It's in that context that Summers' remarks are not helpful."
On the other side are those who believe that biological differences between men and women really can account for at least some of the underrepresentation of women in engineering and some fields of science.
"I think it's an outrage that certain questions -- that real, important questions -- can't be raised in an academic atmosphere, that research that's well-known can't be presented without some sort of hysterical response," said Linda S. Gottfredson, a psychologist at the University of Delaware.
In recent years, scientists have found that male and female brains are wired differently from one another, due to the role of testosterone and other male hormones during gestation. Brains growing under the influence of male hormones are slightly larger and have denser concentrations of neurons in some regions.
Male brains also contain a greater proportion of gray matter, the part of the brain responsible for computation, while women have relatively more white matter, which specializes in making connections between brain cells.
Brain-imaging studies suggest that both sexes exploit these differences to their benefit. UCLA researchers have done brain scans of men and women who scored in the top 1 percent on the math section of the SAT. As they worked on math problems, the men relied heavily on the grey matter in the brain's parietal and cerebral cortices. Women showed greater activity in areas dominated by the well-connected white matter.
"Maybe they're doing the math using the white matter," Haier said. "It's not completely unreasonable."
So men and women appear to use their brains differently in some situations. Does that make any difference in how smart they are?
The short answer is no. Average IQ is the same among men and women.
However, intelligence tests have found that men, on average, perform better on spatial tasks that require mentally rotating or otherwise manipulating objects. Men also do better on tests of mathematical reasoning. Women tend to do better than men on tasks requiring verbal memory and distinguishing whether objects are similar or different. The relative strengths even out, so on average the sexes are of equal intelligence.
Some studies also have suggested that the IQ distribution is more spread out among men. If that is true, then there are proportionately more men at the extremely brilliant end of the IQ scale -- and the dull end as well.
So the reasoning goes like this: Fields such as physics require superb mathematical ability. Not just above average, but really out there.
If men do have a slight advantage over women in mathematical ability, as much of the current research suggests, and there are more men at the extreme ends of the intelligence spectrum, that suggests there is a larger pool of men who can do the heavy intellectual lifting physics requires.
But is the difference really biological, or are exceptional girls and women intimidated by cultural stereotypes and discouraged from cultivating their talents from an early age?
"If I had to guess, the real reason for the lack of women in the upper strata is that there's a comfort zone when you walk into a classroom and see a certain number of people like you," Aronson said.
Aronson and his colleagues have shown that many of the performance differences between men and women, and also between different races, can be erased with minor adjustments that influence test takers' confidence. Tell a group of girls before a math exam that the test does not detect gender differences in mathematical ability and their scores increase.
"This suggests there's something about the testing situation itself," Aronson says. "If there is a biological difference, then it's one that's awfully easy to overcome."
Whatever the reason, researchers have found differences in math ability between males and females from pre-kindergarten through adulthood.
Vanderbilt University psychologists who have been giving exceptionally bright 12- to 14-year-olds the SAT for more than 20 years have found that boys do exceptionally well on the math side of the exam. In a sample of 40,000 children who took the test, twice as many boys as girls scored above 500, four times as many boys scored above 600 and 13 times as many topped 700. The sexes were equally matched on the verbal portion of the test, which is scored on a scale of 200 to 800.
That would suggest there are differences between the sexes in innate ability, the Vanderbilt researchers concluded in various scientific papers.