In 2008, for the first time, U.S. women earned more doctorates in biology than men did. But advanced degrees in other core disciplines of science, technology, engineering and mathematics (STEM) remain stubbornly gender-imbalanced. In chemistry, for instance, women now garner 49 percent of bachelor's degrees but only 39 percent of Ph.D.s. What dissuades so many from further study?

Possible explanations include gender bias, the prospect of short-term postdoctoral jobs that complicate child rearing, and a lack of role models. Female STEM professors are slowly increasing in number, however. “It seems like many of the indicators are pointing toward parity, but at different scales and different rates,” says science education professor Adam V. Maltese of Indiana University Bloomington, adding that fields such as engineering have a long way to go. “That's not going to happen overnight, not in the next decade, and maybe not for the next 20 or 25 years.”

SCIENTIFIC AMERICAN ONLINE

Read more about gender and science education at ScientificAmerican.com/may2013/graphic-science