While the overall birth rate keeps declining, well-educated women seem to be having more children, not fewer. A new report from the Pew Research Centre, based on an analysis of census data, looks at women who have reached their mid-40s (when the vast majority of women stop having children) over the past two decades. It finds that the proportion of all women who reach that age without ever having a child has fallen, but the decline is sharpest among the best-educated women. In 1994, 35% of women with a doctoral degree aged 40 to 44 were childless; by last year, this had fallen to 20% (see chart). Their families are bigger, too. In 1994, half of women with a master’s degree had had two more or more children. By last year, the figure was 60%. It still holds true that the better-educated a woman is, the less likely she is to have a child. But Pew’s data show that the gap has narrowed.

But according to Philip Cohen, a demographer at the University of Maryland, this does not explain the entire leap. Rather, social changes in the nature of marriage seem to be driving the change. Whereas marriage was once near-universal and unequal, in recent decades it has become a deliberate option and more equal. Well-educated women have been able to form strong relationships with similarly brainy men, in which both parents earn and both do some child care. Getting an education and having a career are no longer always a barrier to having children; sometimes, they make it easier.

In 1965, mothers spent seven times as long caring for children as fathers did. By 2012 they were spending “only” twice as much time elbow-deep in formula and Pampers. According to Stephanie Coontz, of Evergreen State College in Washington, how much time fathers spend helping to bring up children is the main determinant of whether mothers will have a second child. For more see