Why You Shouldn't Sign On to the Fear That C-Sections Are Changing Evolution

Mom holding newborn baby
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For hundreds (possibly thousands) of years, Cesarean sections have been around as an alternative to vaginal birth. Though it's possible the surgery has side effects, it's generally considered a pretty great option, and it's likely that C-sections have saved millions of babies' and mothers' lives. However, a new study is claiming that universal popularity of C-sections could be impacting human evolution and telling us we should worry about it. But that doesn't necessarily mean we should.

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The study was published in the Proceedings of the National Academyof Sciences (PNAS) and, using a variety of mathematical formulas and historical data, researchers say they found this: Not only are far more mothers giving birth by C-section than ever before, but many of them are forced to give birth by C-section. The study estimates that in the 1960s, 30 in 1,000 births were done via Cesarean because the baby couldn't fit down the birth canal. They say that today, that number is up to 36 in 1,000, and their model has it spiking even higher in the future.

The authors of the study are saying the reason this number is climbing is because the gene for narrow pelvis size is being passed down, whereas in the past when C-sections weren't as safe or relatively easy, more mothers with narrow pelvises would lose their children during childbirth, which would stop those genes from traveling to the next generation.

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Similarly, babies with large heads would traditionally not make it through childbirth, which would stop those genes from being passed down. But again, because C-sections allow them to live and eventually have kids of their own, they're able to spread the trait for large heads.

It's an interesting idea and fits with Darwin's widely accepted theory of natural selection with only one problem: Natural selection is assumed to take hundreds of thousands of years and it should take many, many generations for any kind of universal shift to take place in the human body. C-sections, though, have only been really popular for the last 50 or so years, which, according to Darwin, isn't nearly enough time for an evolutionary change to occur.

Dr. Nicole Scott, an ob-gyn at Indiana University Health, says it's possible that an evolutionary shift could happen far in the future, but that doesn't mean we should shift focus away from Cesareans and actively try to increase the number of vaginal childbirths again. 

"The alternative is maternal and neonatal morbidity and even death," she explains. "Personally, I would take a C-section over that alternative."

And many women agree. In the US, almost a full third of births are via C-section, and as the study points out, that number is rising. But that's not necessarily a bad thing.

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"A number of factors contribute to that rise," Scott says. "Less VBAC (vaginal birth after cesarean), medicolegal environment, obesity, moms with more health risks (hypertension, diabetes, age), advances in reproductive technology (twins, triplets, getting older mothers pregnant), and more delivery interventions (continuous monitoring, inductions, etc.) are all factors."

Even the researchers said themselves that they don't see a future where vaginal births are obsolete. Even if this trend continues and this evolutionary shift does occur, vaginal birth is still an option that comes with its own set of pros and cons. It's up to the mother and her doctor to decide what's best for each pregnancy, and neither party should let vague-ish studies like this one affect that kind of major decision.

Still, if the study worries you, Scott says you can focus on finding a doctor that only does C-sections when it's necessary, as well as one that allows VBAC.

But really, experts across the board say this study isn't something to worry about. Vaginal births aren't going anywhere, and the effects of an evolutionary shift toward big heads and small birth canals -- even if it does happen -- isn't disastrous by any means. The human race will be just fine.

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