If you want to stay married, three of the most ominous words you'll ever hear are "It's a girl." All over the world, boys hold marriages together, and girls break them up.
In the United States, the parents of a girl are nearly 5 percent more likely to divorce than the parents of a boy. The more daughters, the bigger the effect: The parents of three girls are almost 10 percent more likely to divorce than the parents of three boys. In Mexico and Colombia the gap is wider; in Kenya it's wider still. In Vietnam, it's huge: Parents of a girl are 25 percent more likely to divorce than parents of a boy.
Ever since the economists Gordon Dahl (at the University of Rochester) and Enrico Moretti (at UCLA) established these facts a few months ago, they and their colleagues (and not a few of their colleagues' friends and families) have been spinning hypotheses about what's behind the numbers.
Children of divorce usually stay with the mother, so the question comes down to this: Why do fathers stick around for sons when they won't stick around for daughters? (Or alternatively, why do mothers stay married so their sons can have a father when they won't do the same for their daughters?) Do fathers prefer the company of sons? Do parents think a boy needs a male role model? Do they worry that boys cope less successfully with the emotional consequences of divorce? Or do they believe that an emotionally devastated daughter is somehow less of a tragedy than an emotionally devastated son?
Dahl and Moretti make the extremely helpful observation that all theories fall into one of two categories: Either sons improve the quality of married life (say by being more available for an evening game of catch) or sons exacerbate the pain of divorce (say by falling apart emotionally when the father leaves). Theories of the first sort suggest that a boy child is a blessing; theories of the second sort suggest that the same boy child is a curse—or at least has the potential to become a curse if the marriage starts to crumble.
So, before we decide which theory to believe, we should look for external evidence on the demand for sons versus the demand for daughters. Do most parents prefer boys or girls?
Of course we all know the answer in China, with its ongoing history of female infanticide. But what about the United States? Dahl and Moretti offer several reasons to believe that American parents also have a strong preference—though not as strong as the Chinese preference—for boys over girls.
Here's some of their evidence: First, divorced women with girls are substantially less likely to remarry than divorced women with boys, suggesting that daughters are a liability in the market for a husband. Not only do daughters lower the probability of remarriage; they also lower the probability that a second marriage, if it does occur, will succeed.
Next, parents of girls are quite a bit more likely to try for another child than parents of boys, which suggests that there are more parents hoping for sons than for daughters.
Once again, the effect is strong in the United States but even stronger elsewhere. In the United States, Colombia, or Kenya, a couple with three girls is about 4 percent more likely to try for another child than a couple with three boys; in Mexico it's closer to 9 percent, and in Vietnam it's 18 percent. In China, before the one-child policy was imposed in 1982, the number was an astounding 90 percent!
One of Dahl and Moretti's most striking bits of evidence comes from shotgun marriages. Take a typical unmarried couple who are expecting a child and have an ultrasound, which more often than not reveals the child's sex. It turns out that such couples are more likely to get married if the child is a boy. Apparently, for unmarried fathers, the prospect of living with a wife and a son is more alluring than the prospect of living with a wife and a daughter.
So, what's the bottom line? Dahl and Moretti are quick to acknowledge that they've found no smoking guns; if you're sufficiently clever you can probably concoct alternative explanations for everything they've observed. But the most natural way to interpret their data is that parents, on average, prefer boys to girls. The preference is stronger elsewhere in the world, but it's plenty strong in the United States too.
That seems to answer one question: Boys preserve marriages by making marriages better, not by making divorces worse. But it also raises a new question: What's so great about a boy? Why do parents prefer boys to girls?
Maybe boys grow up to be better economic providers for their parents' old age. (This would explain why the preference for boys is stronger in countries where men hold more economic power.) Maybe boys are just more fun to have around. Maybe parents want a child who can carry on the family name. Or maybe there's something deep in our psyches that tells us a family just isn't a family without a son. Which is it?
Dahl and Moretti wisely decline to speculate, and I will follow their example. I don't know any evidence that could settle this question. All we know is that for some reason, parents prefer boys—by enough that boys hold a lot of shaky marriages together.
Years ago on the schoolyard, we used to chant that girls are good but boys are better. It looks like our parents agreed with us.