Divorce rates are higher for couples who have daughters than couples who have sons, but it doesn’t have to do with the child. Instead, it has more to do with the gender's strength.

Researchers at Duke University looked into the relationship between parents with sons and parents with daughters, and published their findings in the journal Demography. “Many have suggested that girls have a negative effect on the stability of their parents’ union,” the study’s co-author Amar Hamoudi, a Duke economist said in a press release. “We are saying: ‘Not so fast.’”

Previously, research has shown fathers have a preference for sons over daughters and are more likely to stay in marriages that have yielded sons. However, it’s not so much the child’s gender that’s the deal breaker for the parents, but it’s really which embryo can resist a troubled marriage before they’re even born. “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.”

Modern day King Henry VIIIs aren’t divorcing their wives because they gave birth to daughters. These are different times and King Henry VIII, who was notorious in English history for executing four of his wives when they didn’t give birth to male heirs, didn’t have access to the science and research we do today, which tells us women don’t determine the gender, and gender doesn’t determine divorce.

There are over two million marriages in the United States, according to the Centers for Disease Control and Prevention. Of those marriages, most will end in divorce, considering the divorce rate is 59.7 percent.

The analysis was based on a sample of Americans from 1979 to 2010, and subsequently it was found daughters don’t cause parents to divorce, but something deeper and more intrinsic is involved prior to giving birth. It’s the level of conflict a relationship has endured that determines the likelihood of divorce, not the gender of their baby.

From start to finish, girls and women are typically more resilient survivors than boys and men are. By examining females at every age from birth to 100, they survive in much greater proportions than men tend to, which suggests females’ advantage helps them survive stressed pregnancies caused by poor parent relationships.

Research stops short of studying family dynamics during gestation and usually begin observations once the baby is born. Hamoudi and Nobles believe this does a disservice to understanding how family dynamics affect population, and research needs to look into what happens to the months and even years leading up to a child’s birth.

“It’s time for population studies to shine a light on the period of pregnancy,” Hamoudi said. “The clock does not start at birth.”

Source: Hamoudi A and Nobles J. Do Daughters Really Cause Divorce: Stress, Pregnancy and Family Composition," Amar Hamoudi and Jenna Nobles. Demography. 2014.