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Do genes play a role in science gender gap?

Differences are clear; whether they matter is not

Could biological differences between men and women really contribute to men's greater career success in the sciences?

Harvard president Lawrence Summers created a firestorm this month when he suggested that may be the case. Studies indeed show that men's and women's brains aren't exactly the same. The question is whether those differences matter.

Women, on average, get better grades in school, take math and science classes at the same rate, and earn roughly the same number of bachelor's degrees in science and engineering as men. But when it comes to graduate school and jobs, they tend to leak from the career pipeline. A swirl of factors including childbirth, cultural norms, societal expectations, and psychology more likely explain why they become scarcer at the highest ranks of science and math, researchers said.

Summers drew on one, perhaps discomforting, scientific observation: According to IQ tests and national science and math exams, more men than women get the lowest scores -- and the highest.

''More geniuses, more idiots," said Steven Pinker, a Harvard psychologist whose book, ''The Blank Slate: The Modern Denial of Human Nature," helped inform Summers' comments at a Jan. 14 conference on diversity in the scientific workforce.

Pinker said one explanation for this finding may lie in a tenet of evolutionary biology, which holds that organisms try to maximize the survival of their genes in future generations. According to this theory, because men can have many more offspring then women, nature takes more risks with the genes that parents pass on to their boys. One result is that men are more likely than women to end up at the extremes of intelligence.

But there are other possible explanations for this finding, ranging from test bias to a well documented ''stereotype threat" -- a feeling of discomfort when women fear that they may fulfill a negative stereotype about their group.

Women's math scores are also known to fall when the proportion of men in the room increases, a further indication that test scores are an imperfect measure of ability.

Summers was faulted by some conference participants and others for drawing a link between test scores and career success -- a link that they said has been disproved by research.

Yu Xie, a sociology professor at the University of Michigan who spoke at the conference, has shown that men outnumber women 2-to-1 in the top 5 percent of scorers on math tests -- research that Summers cited in his talk. But Xie said in an interview that his studies show that not all the best scorers succeed professionally, and not all men with successful science careers received the top scores.

Xie and Kimberlee Shauman of the University of California at Davis, who coauthored ''Women in Science: Career Processes and Outcomes," concluded that no single factor could explain why women did not make it into the most elite science positions, and that a combination of social, cultural, and psychological factors were probably at work.

Some social scientists believe that the culture of science itself has a built-in masculine bias, including everything from tenure schedules that conflict with the child-rearing years to a scientific culture that favors male personalities and management styles.

While some biological biases are believed to be inborn, social reinforcement probably plays a bigger role than genetics in, say, girls' love of dolls and boys of trucks.

''Those get sort of intensively reinforced from the get-go, and true potential is hard to measure," said Lise Eliot, a neuroscientist at Rosalind Franklin University of Medicine and Science in Chicago who studies cognitive sex differences.

Brain studies do show that males and females have slight biological differences. Women tend to use both sides of the brain when they think, while men use only one; men have slightly larger brains; women tend to be better at doing computations in their head. But no one understands the implications of these differences, if there are any at all.

The science of gender differences is clouded by a long and dismal history of sexist pseudoscience. In the late 1800s, when women first began to be admitted to universities, some male scientists feared that mental exertions would draw blood away from women's ovaries. Just as the science of eugenics was used to support racism, evolutionary arguments were used to argue that women should be prepared for professions that drew on average ability, not extreme giftedness.

Researchers are still struggling to explain why inequalities persist.

''What I can say is that if biology plays a role, it should interact with the environment . . . so social factors can still make a big difference" in career success, Xie said. ''It cannot be due to biological factors alone."

Carolyn Y. Johnson can be reached at

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