[kansface]

Women make up about 50% of undergrad chemistry degrees. On the other hand, they make less than 20% of physics/math degrees (engineering funnels). I don't have any real idea why women are so low in math and physics, but I suspect you'd have to look back much further in time.

[tomp]

I studied math in Slovenia. There were about as many female as there were male students. In financial mathematics (and e.g. pharmacy, IIRC), there were more women than men. On the other hand, in computing and physics there were more men than women.

I am very inclined to think this is mainly a matter of preference. On the other hand, maybe the situation in the US is completely different, and Slovenia is just so much more equal when it comes to sex (e.g. the unadjusted gender wage gap is only 2.5% for Slovenia).