Thursday, October 29, 2009

Childbirth and Evolution

From Half the Sky:

"One reason women die in childbirth has to do with anatomy, arising from two basic evolutionary trade-offs. The first is that once our ancient ancestors began to walk upright, too large a pelvis made upright walking and running inefficient and exhausting. A narrow pelvis permits fast running. That however makes childbirth exceedingly difficult. So the evolutionary adaptation is that women generally have medium-sized pelvises that permit moderately swift locomotion and allow them to survive childbirth - most of the time.

The other trade-off is head size. Beginning with our Cro-Magnon ancestors, human skull size expanded to accommodate more complex brains. Larger brains offer an evolutionary advantage once a child is born, but they increase the chance that a large-headed fetus will never emerge alive from the mother."


Demers said...

Commentary? Are you trying to explain why the average woman doesn't run as fast as the average man?

Dan said...

yeah that's one thing i think you can take from it.

i actually always wondered why evolution didn't make pregnancy less difficult/deadly - this makes some sense