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We May Finally Know Why Couples with Firstborn Daughters Are More Likely to Divorce

Researchers solve link between daughters and divorce
Photograph by Getty Images/iStockphoto

It's nothing new: Studies have been telling us for years now that our marriages are more likely to end in divorce if our first child is a girl. Yep, that may sound like one big depressing old wives' tale when you first hear it, but believe it or not, it's been scientifically proven over and over again. Here's the thing, though — we've never really known why.

Of course, there were plenty of far-fetched theories out there. Most notably, this head-scratcher — that dads tend to bond more with their sons, and therefore are more willing to make their marriage work if their firstborn is a boy. (Something about him being more willing to keep the family unit intact if he's closer with the first kid? Beats us.) But those theories never seemed to be rooted in any sort of factual evidence.

No matter, because, according to a new study published in "Demography," we can throw all our previous hypotheses right out the window, because the truth behind it all is far more complicated than we ever thought. Researchers now say the answer lies in a key developmental difference between male and female fetuses — meaning the whole matter starts long before our kids even make their way into the world.

When looking further into this connection, researchers Amar Hamoudi and Jenna Nobles discovered that female embryos are often better able to withstand any stress the mother is experiencing while pregnant (including any relationship troubles). Male embryos, on the other hand, fare less well and have a much lower survival rate. In other words, if Mom's marriage is on the rocks while she's pregnant, her female fetus is much more likely to make it to full-term. And as we already know, stress hormones during pregnancy have a pretty powerful impact on Mom's body and her baby.

What's so interesting about all of this is that it brings up the concept of a "female survival advantage," which has long been accepted in research circles. After all, we hear it all the time that women live longer than men — that's because it's true. But the fact that this is happening as early as the embryo stage? Pretty fascinating stuff.

It was this very concept of a female survival advantage that led Hamoudi, an assistant professor of public policy and economics at Duke University, to examine the link between firstborn daughters and divorce in the first place.

"What I wondered was, why are we starting the story at 40 weeks after fertilization?" Hamoudi told The Huffington Post. "Why don't we start at fertilization? Then it's a much more complicated story."

Indeed it is.

"We didn't prove that girls don't cause divorce," added Hamoudi. "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."

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