C-sections might be relaxing the evolutionary pressure against big babies

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Theoretical biologist Philipp Mittericker is intrigued by the puzzle of dangerous human childbirth. Unlike other species, human babies are often too big for the birth canal, leading to dangerous-and possibly fatal-obstructed labor. Last year, Mittericker and his colleagues published a mathematical model that showed how the mixture of evolutionary pressures acting on humans would inevitably lead to an ongoing risk of obstructed labor in our species.

The model also suggested that C-sections are changing the rules of the game by increasing the likelihood that large babies and their mothers survive childbirth and pass on genes that promote this head/pelvis mismatch. The model predicted that we'd see an increasing risk of obstructed labor (and need for C-sections) over generations-but there was no real-world evidence of that happening.

Now, in a new paper, Mittericker and colleagues have published empirical evidence that this is indeed the case: women who were born by C-section seem to have a higher risk of needing a C-section themselves. And the real-world increase in risk is similar to what their model predicts.

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