The voluntarily childless do seem over-represented in our sample. Most American women—about 67 percent, according to a 2009 study by Ohio State University sociologist Sarah Hayford —decide as teenagers to have two children, and they roughly stick with that plan. Another, smaller group starts out wanting three or more kids and ends up having more than the average two; yet another segment starts out wanting two, but they wind up with fewer. Those like me are statistical freaks, making up just 4 percent of the population: We start out wanting kids … we guess? Maybe one? Our expectations decline with age, and, Hayford writes, “by their early 30s, these women expect to have no children.” (Her study was of women who were 18 in the 1980s; it’s not clear if the views of today’s women would evolve differently.)

Childlessness rose steeply from the 1970s to about 2005—it has since declined again—and Hayford found that a decline in marriage rates contributed most to that rise. Getting married can change people’s minds about having kids, she says. To some, “marriage means having children, so I’m entering this married world and taking on other things that go along with it,” Hayford said. (As one reader put it to us: “I’ve always said that I never knew I wanted children, until I knew that I wanted children with him.”)

Today, about 15 percent of women never have kids, but most of us start out agnostic. “There are not that many people who, early on, say, ‘I definitely don’t want kids,’” said Amy Blackstone, a sociologist at the University of Maine. Even the childless are more likely to start out unsure or assuming they will have kids. It’s only over time that they decide against it.