U.S. statistics reveal that couples with daughters have a higher likelihood of divorce, which led some scholars to interpret the data as evidence that daughters cause divorce. A new Duke University study refutes the claim finding that girls are hardier than boys in the womb, an advantage explaining the higher likelihood of girls surviving stressful pregnancies in a troubled marriage.
“Many have suggested that girls have a negative effect on the stability of their parents’ union,” said Duke economist Amar Hamoudi, who co-authored the study published July 15 in Demography with Jenna Nobles, a University of Wisconsin-Madison sociologist. “We are saying: ‘Not so fast.’ What about all those pregnancies that don’t end up in a live birth?”
Females are generally hardier than males, surviving in higher proportions than men in all stages of life. The robustness of female embryos may explain why couples with daughters are more likely to divorce, reports Hamoudi a teacher at Duke’s Sanford School of Public Policy.
The female survival advantage may even begin in the womb. Epidemiological evidence suggests that female embryos withstand the biochemical stress response of mothers in strained marriages, explains Hamoudi. This advantage may allow females to withstand stressful pregnancies more than males.
“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.”
But these differences are very small. In a given study period, about two percent of couples with first-born sons will divorce and 2.1 percent of couples with first-born females will divorce, says Hamoudi.
Based on the study’s analysis of U.S. demographic data over 31 years, researchers say relationship conflict predicts their probability of divorce. They also found that relationship conflict predicted the sex of children born by that couple later in life, with more females born to couples that experienced marriage problems.
The study reveals that the months prior to birth can influence patterns in populations, a period often overlooked by demographers.
“It’s time for population studies to shine a light on the period of pregnancy,” Hamoudi said. “And the big challenge here is how limited the population level data are.”
A congressionally mandated National Children Study seeks to address this data gap by following cohorts of children through time. The long-term study is currently in the planning phases. Hamoudi and Nobles continue to study how pregnancy influences demographic patterns with the data that exists.
The research was supported in part by the Center for Demography of Health and Aging at the University of Wisconsin-Madison.