C-sections May Be Changing the Course of Evolution

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Rates of caesarean section are increasing in countries like the U.S. and the U.K. and a new study suggests that more and more women need the surgery because of their narrow pelvis size — a trait that evolution would, in theory, have weeded out.

For the paper, published in the journal Proceedings of the National Academy of Sciences, researchers used data from the World Health Organization and other large birth studies and determined that cases where the baby is too big for the birth canal — a.k.a. obstructed birth — have increased from about 30 per 1,000 in the 1960 to 36 per 1,000 today.

It could be the result of narrow pelvises, large babies, or both. But in the past, these babies (and some of their moms) might have died during labor and the woman’s genes would not have been passed on. “Without modern medical intervention such problems often were lethal and this is, from an evolutionary perspective, selection,” study author Philipp Mitteroecker, Ph.D., of the University of Vienna, told the BBC.

Mitteroecker said that the paper isn’t criticizing the procedure, but rather pointing out its effects. He also believes that the trend will continue, but C-section births won’t overtake vaginal ones. An obstetrician not involved with the study told the BBC that other factors, like diabetes and obesity, could also lead to larger babies, and thereby more C-sections. This study can’t definitively say that surgery is affecting the course of evolution but it might be. Add pondering that concept to your list of things to do before your due date.

C-sections May Be Changing the Course of Evolution