[Reposted from comments]

Noah and I were discussing this over breakfast this morning [18 Jan]. (Yes, Noah got up before 9!) He suggested that the proportion of top-rank women chess players or mathematicians could never be more than about a third, because boys are more likely to be obsessed to the point of becoming really good at those subjects. I pointed out that the number of top-rank female (classical) musicians is approaching a half, and that requires no less obsession.

Even if there is some minuscule biological basis, it couldn't possibly be enough to explain the current discrepancy, so the debate is irrelevant until we do better.