To the Editor:

I was interested to read that women now outnumber men in the geology major (“In geology, women undergrads outnumber men,” 11/28). The same is true in the astronomy department — we don’t have enough majors in any given year to provide good statistics, but over the past five to seven years women have outnumbered men by a considerable margin.

As with the geology department, this is not just a Yale phenomenon. Within the past few years, the number of women majoring in astronomy nationwide surpassed the number of men majoring in that field for the first time. This contrasts dramatically with the situation in the early 1990s when men outnumbered women almost two to one in undergraduate astronomy programs.

It’s not clear what has caused this sudden change in demographics. But one explanation can be ruled out — the ratio of men to women in these fields of science cannot be governed by innate gender-linked differences in ability, as Harvard’s President Lawrence Summers famously suggested. Even if one were to postulate that a recent genetic mutation has somehow increased the scientific ability of women, such a change cannot propagate through a population in less than a single generation. On the other hand, cultural expectations surely do change on time scales of a decade, so explanations of that kind fit the facts.

Charles Bailyn ’81

Nov. 28, 2005

The writer is a professor of astronomy.