Despite steady advances, women are still rare in math-based fields such as physics and engineering. The cause lies not in a fear of math but in socialization, say psychologists Jacquelynne Eccles and Mina Vida of the University of Michigan. Using interviews and questionnaires to assess behavior and values, they monitored 1,700 girls and boys over a period of 20 years. The data indicate that girls' math abilities outpace boys' through high school, but the girls eschew math-oriented careers because they do not believe such careers are valuable to society. "Those girls who are good at math seem to be going into the biomedical sciences, where you produce something that you can see will make a difference to people," says Pamela Davis-Kean, codirector of Michigan's Gender and Achievement Research Program.
Although the dearth of women in the mathematical sciences has long been attributed to low self-esteem and underencouragement from teachers and professors, Davis-Kean says the study suggests an earlier influence: parents. "Girls have friends over or play with dolls, whereas boys are directed to build things they can do on their own. Girls have math ability—they're using it, and they're getting M.D.'s and Ph.D.'s—but they're not getting engineering degrees. We think that has to do with what they value."