When Lawrence Summers, then head of Harvard University, said in 2005 that innate gender differences may be a reason why fewer women succeed in math and science careers, he ignited a firestorm. Women's groups were outraged. Academic societies issued rebuttals. Angry columnists weighed in.

And three Cornell University researchers hit the books.

After wading through more than 400 academic articles on sex differences in math, they've concluded that it's not a lack of ability that keeps women from pursuing careers in engineering or computer science. Rather, it's a variety of factors, including a female preference for more people-oriented professions and significantly different lifestyle needs, such as having and raising children.

The study, published today in Psychological Bulletin, a journal of the American Psychological Association, also explains a glitch in the gender gap. Among those who score at the top of the heap in math, the girls also tend to excel verbally while the boys don't. Hence they have more choices, career-wise. Advantage: girls.

"For the boys with high math ability, it's `This is my strength,'" explains the study's lead author, Stephen Ceci. "For the high-math girls, it's `This is one of my strengths.'"

So take that, Lawrence Summers – yes?

"Absolutely," laughs Ceci, professor of developmental psychology at Cornell.

Summers, now a White House economic adviser, also alluded in his 2005 remarks to a reluctance of mothers to work 80-hour weeks. The Cornell team found that women are under-represented, not only in math-intensive fields, but in senior posts in most fields because the demanding mid-career period clashes with their biological clocks.

Academia and other sectors need to adjust tenure and promotion paths to tap more fully into the reservoir of female talent, Ceci says. "We pay a lot of money to train people and we're not taking advantage of their human capital."

The Cornell researchers spent more than three years examining gender-difference findings in endocrinology, educational psychology, sociology and other fields.

Promoters of the innate-superiority argument in math, Ceci says, point to U.S. student aptitude tests, in which boys typically outnumber girls two to one among the top 1 per cent of scorers. But if that was a conclusive indicator, he argues, U.S. women would still claim 33 per cent of the spots in math-intensive fields such as engineering. In fact, their numbers are far less.

In Canada, women make up only 17.5 per cent of undergraduate engineering programs.

But in some other countries, Ceci says, female students actually outnumber boys in the elite math tiers. So scratch off biology as the sole explanation, he says.

The Cornell researchers also eliminated bias and discrimination as primary factors.

"It came down to preferences," says Ceci. A female is more likely to find medical research – finding a cure for a disease – more personally fulfilling than developing an Internet search algorithm, he says.

In U.S. undergraduate programs, 48 per cent of math majors are female, says Ceci. But they are drawn to medicine or the biomedical sciences, not math-intensive fields like physics or computer science. "These preferences start as early as junior high school," he says.

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Will female numbers in engineering and physics grow over time?

The gap "will probably narrow, but not fully close," says Ceci. "They won't be at parity with the boys."