Born too soon

Can evolution guide the search for genes involved in preterm birth?

Leigh MacMillan, Ph.D.
Published: June, 2010

We humans are a big-headed lot. We need the space for our large brains – they’re what make us human, after all. But our outsized pates are not so optimal when it comes to being born and fitting through the female pelvis, narrowed by our fondness for walking on two legs.

It usually works – we’re born before our heads get too big to fit. Evolution finessed the parameters to get it right, posits Louis Muglia, M.D., Ph.D.

“We think that human pregnancy had to adapt and push the time of birth to the earliest compatible with optimal survival for both the mom and the fetus,” says Muglia, Edward Claiborne Stahlman Professor and vice chair for Research Affairs in the Department of Pediatrics at  Vanderbilt University Medical Center  .

 Big heads, narrow hips
The large opening of the chimpanzee pelvis (panel A) permits easy passage of the relatively small fetal head. In the extinct, humanlike primate of the genus Australopithecus, (panel B), the widening of the ilium associated with upright posture and the front-to-back narrowing of the pelvic opening required the head to be delivered sideways. The human pelvis (panel C) has an opening just large enough to allow passage of the fetal head facing the mother’s spine.
From the January 18, 2007, issue of The New England Journal of Medicine (volume 356, page 272).
Courtesy of The New England Journal of Medicine

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