Research into why families with firstborn daughters are slightly more likely to divorce than those with firstborn sons has disproved the long-held reasoning that men simply prefer sons. Scientists at Duke University in North Carolina have found that female embryos are hardier in the womb, so they are more likely to reach full term if the expectant mother is in a stressful relationship.
Duke University economist Amar Hamoudi said in a press release: ‘Many have suggested that girls have a negative effect on the stability of their parents’ union. We are saying: “Not so fast.”‘ Hamoudi, who co-authored the study with Jenna Nobles, a University of Wisconsin-Madison sociologist, believes it has to do with the ‘robustness of female embryos.’ ‘Girls may well be surviving stressful pregnancies that boys can’t survive,’ Hamoudi said. ‘Thus, girls are more likely to be born into marriages that were already strained.’ According to the research paper, published in Demography, taxing events – such as a problematic relationship – can lead to unhealthy levels of stress hormones, which, in turn, can lead to reduced fecundity.
The biological system that regulates the stress hormones overlaps substantially with the system that regulates progesterone, a hormone vital to a successful early pregnancy. And, at the end of pregnancy, stress hormones are directly involved in finalizing the fetus’s organ development and inducing labor. Interestingly, during the course of their study, Hamoudi and Nobles also found that couples who had struggled at any given point in a relationship were more likely to have girls in subsequent years. The pair based their research on longitudinal data from a nationally representative sample of U.S. residents from 1979 to 2010.
Females are hardier than men in general not just before birth: ‘At every age from birth to age 100,’ the study’s press release says, ‘boys and men die in greater proportion than girls and women.’ Hamoudi and Nobles’s research also points out an interesting flaw in population studies done up to this point: Very few, if any, consider the months before birth, which, as Hamoudi says, is important in understanding how family dynamics affect populations. ‘It’s time for population to shed light on the period of pregnancy,’ he said. ‘The clock does not start at birth.’
In the research paper’s conclusion, it says that their studies could lead to more investigations: ‘Because marriage and nuclear families are no longer the dominant environment of fertility and child-rearing in the United States, it may be worth extending this inquiry to outcomes other than divorce.’ They say it might be useful to extend their approach to apply to nonmarital unions or to investigate outcomes other than just relationship stability, like sex-specific child support payments. -dailymail
