Physics is among the most male-dominated of disciplines. And while commentators bandy about many possible causes -- discrimination, the lifestyle tradeoffs required by graduate school or the academic workplace, and, controversially, innate aptitude -- the problem seems most directly attributable to female students abandoning physics in droves between high school and college.
So concludes a report  issued last week by the American Institute of Physics, which found that the relatively small proportion of female faculty members in the field occurs not because of a "leaking" pipeline within academe, but because of the small proportion of women who choose to study physics after 12th grade.
The report, "Women in Physics and Astronomy, 2005," was prepared by Rachel Ivie, a sociologist who is a principal research associate at the physics institute. Her study, a followup to a 2000 report, finds that more women are studying physics now than at any time in history: In 2001, they made up almost half of the 930,000 high school physics students, and in 2003, women earned 22 percent of the physics bachelor's degrees awarded, and 18 percent of Ph.D. recipients, a record high.
But those numbers tell another story, one that gains added moment because of the hubbub  surrounding comments made last month by Harvard University's president, Lawrence H. Summers, suggesting that women may be underrepresented on college science faculties, and in the sciences generally, because of some "innate" differences between the genders.
In an interview, Ivie had no interest in wading into that controversy. But the data in her report show a steep dropoff between the proportion of women studying physics in high school and then receiving bachelor's degrees. Exactly why that's happening is unclear, she says, but she speculates that "many girls take high school physics because they want to get into college, but by the time they're in college, they've already been well-set on certain career paths" that tend not to include a hard science like physics.
"For better or worse," Ivie adds, "by that time they've had 18-20 years of socialization already in the perception of our society that the physical sciences are 'what guys do,' and physics is the most fundamental of the physical sciences." (Her report notes, by comparison, that women receive 46 percent of the bachelor's degrees in astronomy.)
From that point in the academic pipeline on, though, women do not seem to get driven out of physics in any significant way, the AIP report finds. For instance, in 2002-3 academic year, women earned 22 percent of physics bachelor's degrees, and the following fall, they made up 21 percent of the entering class of physics graduate students nationally.
Similarly, Ivie suggests, women do not drop out of graduate school at higher rates than men do: In 2003, women earned 18 percent of physics Ph.D.'s, and seven years earlier, 17 percent of entering graduate students were women.
And 16 percent of assistant professors of physics are women, even though women earned only 12 percent of physics Ph.D.'s awarded from 1991 to 1997, when the middle 50 percent of assistant professors earned their Ph.D.'s. That means, Ivie says, that "women are more highly represented on physics faculties at the assistant professor level than we would expect."
Just because women are represented in physics at the rates that one would expect, Ivie says, "doesn't mean that they haven't suffered from discrimination in other ways." She notes, for example, that "even when working in the same employment sector with the same years of experience, women in physics and related fields on average earn less than men."