In the United States couples with daughters are somewhat more likely to divorce than couples with sons. Many scholars read this as evidence that daughters cause divorce. And until recently, sociologists and economists attributed the connection between daughters and divorce to a polarizing theory: Fathers relate to sons better, so they’re more likely to struggle with a problem marriage if they have a boy.
But research from Duke University suggests something quite different may be at play: Girls may be hardier than boys, even in the womb, and may be better able to survive pregnancies stressed by a troubled marriage. In short, couples with girls more likely to divorce, but girls may be a symptom, not the cause.
Previous studies have argued that fathers prefer boys and are more likely to stay in marriages that produce sons; conversely, the argument runs, men are more likely to leave a marriage that produces daughters. That assessment has been around for decades, and the conventional wisdom is axiomatic in popular culture.
The Duke study, which appeared online in the journal Demography, suggests a very different potential explanation for differing divorce rates: the robustness of female embryos. “Many have suggested that girls have a negative effect on the stability of their parents’ union,” says Duke economist Amar Hamoudi, who co-authored the new study with Jenna Nobles, a University of Wisconsin-Madison sociologist. “We are saying: ‘Not so fast.’ ”
Hamoudi, who teaches in Duke’s Sanford School of Public Policy and is a fellow of the Duke Center for Child and Family Policy, argues that throughout the life course, girls and women are generally hardier than boys and men. At every age from birth to age 100, boys and men die in greater proportions than girls and women. Epidemiological evidence also suggests that the female survival advantage actually begins in utero. These more robust female embryos may be better able to withstand stresses to pregnancy, the new paper argues, including stresses caused by relationship conflict.
Based on an analysis of longitudinal data from a nationally representative sample of U.S. residents from 1979 to 2010, Hamoudi and Nobles say a couple’s relationship conflict predicts their likelihood of subsequent divorce.
Strikingly, the authors also found that a couple’s level of relationship conflict at a given time also predicted the sex of children born to that couple at later points in time. Women who reported higher levels of marital conflict were more likely in subsequent years to give birth to girls rather than boys.
“Girls may well be surviving stressful pregnancies that boys can’t survive,” Hamoudi said. “Thus girls are more likely than boys to be born into marriages that were already strained.” If a mother is experiencing a rocky relationship from the outset, her female fetus has a better chance of surviving the full term. This theory of characteristic female survival advantage — meaning girls and women of all ages are more likely than boys or men to make it to their next birthday — is a widely accepted concept in research, but Hamoudi and Nobles’ findings are particularly noteworthy because they show that this survival advantage may start in the womb.
Hamoudi and Nobles also make a broader point that reaches beyond the issue of divorce. Population studies typically begin at birth, Hamoudi said. Yet if demographers and other social scientists want to fully understand how family dynamics affect populations, they need to consider the months before birth as well. “It’s time for population studies to shine a light on the period of pregnancy,” Hamoudi said. “The clock does not start at birth.”
They found that nearly all of the links between daughters and divorce could be accounted for by stress-related dynamics during pregnancy.
“We didn’t prove that girls don’t cause divorce,” he said. “What we proved was that it would be hasty to look at the daughter-to-divorce association and say, ‘Aha, girls must cause divorce,’ because we now have another explanation for why that association might exist.” Before social scientists jump to conclusions about the link between daughters and divorce, they need to start the clock at fertilization, not birth. Otherwise, they’re missing a key piece of the puzzle.