In graduate school, if not before, women begin to learn that science and families don't go well together. They can't help but notice that most of their advisors and mentors are men. Moreover, less than one half of tenured female faculty all disciplines are married with children. Consequently, aspiring female scholars don't have a lot of role models, especially those who've managed to combine marriage and children with a successful career in academic science. Due in part to the paucity of role models, about 30 percent of the women--and 20 percent of the men--we surveyed at the massive ten-campus University of California system turn away from their goal of becoming a professor at a major research university. "I could not have come to graduate school more motivated to be a research-oriented professor," one woman told us. "Now I feel that can only be a career possibility if I am willing to sacrifice having children."

The most significant winnowing out of women occurs right after fledgling scientists finish graduate school. It has long been known that women are less likely than men to snag tenure-track positions. National data from the authoritative Survey of Doctorate Recipients shed light on this disparity. The married mothers of young children--that is, children too young to attend school--are 35 percent less likely to get tenure-track jobs compared with married fathers of young children. The same women are 33 percent less likely to get jobs compared with unmarried women who aren't the parents of young children. However, unmarried childless women are four percent more likely to get tenure-track jobs than are unmarried childless men. At this professional turning point, family formation probably explains why female scientists don't get tenure-track jobs.

Why do marriage and motherhood have such profound consequences for women's job market prospects? Married female scientists are almost always in dual-career marriages, while only around half of male faculty have wives who work full-time. One spouse must defer, and that spouse is likely to be wife (unfortunately we have no data on same-sex unions, or nonmarital live-in relationships). And unlike in most other professions, taking an academic job typically requires relocation to another state. The baby penalty is even easier to understand. Many women are loath to face the demanding "publish or perish" assistant professor years while caring for young children; cognizant of this challenge, some academic search committees are reluctant to hire women perceived to be on the mommy track rather than the tenure track. These problems persist because the rigid academic career structure really doesn't offer women any good time to have children.

Over the past decade these issues have come to the attention of universities in the United States and abroad. Many sensible policies have been introduced in an attempt to make academia more family friendly. Two of the most common are tenure-clock stoppage and parental leave. Although these interventions are important, they are not enough on their own. They raise numerous complications, but in the interest of brevity I'll name only two. First, these policies need to be entitlements, rather than special accommodations that have to be requested and approved. Second, they need to be available to and used by men and women alike. Our review of the 59 top research universities in the United States showed that as recently as 2008, female academics were over three times as likely as their male colleagues to be entitled to at least six weeks of unrestricted parental leave. Traditionally many faculty members, especially women, have not availed themselves of these family-friendly programs because they perceived a stigma in doing so. This is why both men and women must take parental leave and tenure-clock extensions (such is the lesson from Sweden, where use of parental leave expanded when men were urged to make use of it).