The Nobel science prizes were announced this week, and as is often the case, there were no women among the winners. Many women have risen to the top ranks in science and engineering, but many disciplines ? especially in the physical sciences and engineering ? have remained solidly male bastions. As we hear from VOA's Art Chimes, there is a lively debate about why that is.

Is it because of sex discrimination, or preference, or innate ability? Many scientists don't see any significant gender differences that would explain the disparity. Among them is Elizabeth Spelke of Harvard University. In her lab, she tests very young children on skills that represent the kinds of thinking needed for careers in science and finds that, in general, boys and girls perform about the same.

"I think what we see is evidence that boys and girls are equally endowed with the core cognitive abilities at the root of science and mathematics and in light of those findings," Spelke said, "we shouldn't be surprised by the statistics that show that today, girls and boys perform equally well in math and science subjects, both in high school and in college."

A report last year from the prestigious National Academy of Sciences agreed. It found that women were well-represented as students in many fields of science and engineering, but were less likely to advance to senior faculty jobs at top universities. The report concluded "women are very likely to face discrimination in every field of science and engineering."

But some researchers insist there are gender differences that might explain why fewer women are advancing in science and engineering. Richard Haier of the University of California (Irvine Medical School) has been doing brain scans of men and women as they perform different tasks, and identified functional differences in the way the brain works.

"The harder the brain was working here in the men, the better they did on math," he said. "There was no such relationship in the women. The women were just as good [at] math; how they did it, according to this study, remains a mystery. We know almost nothing about whether sex differences in cognition ? even where there are some, and in most places there aren't ? but even where there are some, we know almost nothing about the brain."

The scientists spoke at a seminar organized by the American Enterprise Institute, a Washington think tank generally described as conservative. Also on the panel was British researcher Simon Baron-Cohen of Cambridge University. He described a study in which boys and girls were given a variety of toys to play with. They were free to choose whatever toy they wanted.

The boys tended to prefer construction toys like Legos and vehicles; the girls preferred dolls, and indeed created whole stories around them. These were young children, but researchers wondered if perhaps they had already been socially conditioned to choose what they thought were gender-appropriate toys. So Baron-Cohen said a similar experiment was done using animals ? vervet monkeys ? with similar results.

"The male monkeys spend more time pushing along these toy cars, and the female monkeys spend more time examining and interacting with these dolls, which just hints at the possibility that even though culture is important ? we heard earlier about the toy industry targeting our kids in different ways and the effects of cultural experience ? it may be that biology is also an important factor to include."

Elizabeth Spelke, the Harvard researcher, acknowledges there are differences between males and females. But she says that shouldn't distract from the impact of cultural factors. "One thing that I don't think anybody can disagree on is that there are biological differences between men and women. But we also know that cultural expectations and norms have an enormous influence on those choices. What people think of as possible lives for themselves is very influenced by what they see as appropriate, what they see as possible and open to them, and these are very open to change."

The National Academy of Sciences' panel that studied discrimination against women in the sciences was led by Donna Shalala, a former cabinet secretary under President Clinton and now president of Miami University. She agrees that expectations of what women should do is keeping them out of senior positions at top research institutions.

"I think it's not a lack of talent," Shalala insists. "There are unintentional biases, and some of them are held by women as well. It's very difficult for you to have a family and spend the kind of time in a laboratory that you need to spend. We have timelines on getting to tenure that may have nothing to do with the quality of your work. The most fundamental point is that we can't afford to underuse half of our human talent in our country."

Some areas of science ? mechanical engineering, for example ? remain overwhelmingly male. Women have done much better in medicine and the life sciences. And in one particular field, some three-quarters of the students are now women: veterinary medicine.