Are Female Embryos Hardier Than Male Embryos?

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New research from Duke University suggests that girls may be hardier than boys in the womb, and therefore better able to survive pregnancies stressed by troubled marriages. In a study that appears in the July issue of the journal Demography, Duke economist Amar Hamoudi and University of Wisconsin sociologist Jenna Nobles link differing divorce rates to the robustness of female embryos.

According to the study, at every age from birth to age 100, boys and men die in greater proportions than girls and women. Epidemiological evidence 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 study suggests, including stresses caused by relationship conflict.

The authors also found that a couple’s level of relationship conflict at a given time 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 says. “Thus, girls are more likely than boys to be born into marriages that were already strained.”
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Katherine Kopp is a freelance writer and editor in Chapel Hill.

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