From U.S. Census Bureau data, we know that, among women who were finishing their childbearing years (ages 40-44) in 2010, those with less than a high school degree had borne the most children (2.56), and those with advanced degrees had the fewest (1.67). (Last's comment that "Women who go to college or graduate school are unlikely to have even two children" seems to follow from the fact that college graduates have an average of 1.73 children, but it's not true. Because about one in every five college graduates have no children, we only get to an average 1.73 because about half actually have 2 or more children.

But this does not mean that, "The bearing and raising of children has largely become the province of the lower classes." That's because only 10 percent of these women had less than a high-school degree, while 34 percent had achieved a BA degree or higher. So here is the distribution of children according to their mothers' education level, next to the distribution of women:

You can see that women with the least education did have more kids than their share of the population: 14 percent versus 10 percent. But there were twice as many children born to women who were college graduates. So women with higher education are almost doing their share in producing the workers of the future. When it comes to childbearing, in other words, the highly educated are almost pulling their weight.

Fact 2: Educational disparities in fertility rates are decreasing

Among women reaching the end of their childbearing years, the last 15 years have seen a decline in the disparity I just described. Completed fertility rates have increased for those with more education, and decreased for those with less, from 1995 to 2010:

Remember that, even though their fertility rates are quite high, high school dropouts represent only 10 percent percent of women ages 40 to 44.

To be sure: There are a lot of different ways of measuring fertility rates. I'm using completed fertility—the number of children even born to women who reach the age at which childbearing becomes rare (the census defined this as ages 35 to 44 until 2002, and ages 40 to44 since). And this shows women with less education having more children. However, in any given year, women with higher education are more likely to have a child. That's because people spend fewer years with advanced degrees; that is, women who end up with advanced degrees spend years without them first, usually not having children while they advance their educations and careers. So in 2011, women with MA degrees or higher were just 9 percent of women in the childbearing ages, but they had 11 percent of the babies.

The counterintuitive thing here is the rise in fertility among women with more education (which Last might be pleased to be able to call Darwinian). I could suggest a few reasons for this:

Maybe the advanced degree holders at age 40 in 1995 were trailblazers, who, in their struggle to succeed against the prevailing sexism, chose career over children. Meanwhile, women in law or medicine are more common today—and we've learned a little more about combining child-rearing with professional careers. (Which often involves paying poorer women to do more caregiving work, which might lead them to have fewer children).

to have fewer children). Or, maybe post-feminist professional women have come to care less about their careers and choose, perhaps under duress, more childrearing instead. If that is the case, it might be contributing to the stall in progress toward gender equality and the ratcheting upward of competitive parenting.

Maybe our intractable work-family conflict—no paid leave, no universal preschool, inflexible workplaces and long workweeks, fathers' inflexibility—has forced women to choose between parenting and professional success, and more have decided parenting is the more fulfilling.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.