Human babies barely fit through the birth canal. And even after all that trouble, newborns come out … well, helpless. Unlike baby chimpanzees, who are basically tiny adults, human babies spend a whole year learning to sit up, walk and talk. It’s a conundrum that’s left many anthropologists wondering why we evolved this way.
Hips are the usual suspects. For nearly a century, scientists hypothesized that the hips face an “obstetrical dilemma” — they must be narrow enough to allow us to walk on two legs but wide enough to birth big-brained babies. Evolution’s solution, the argument goes, was to truncate gestation so that lesser developed newborns can squeeze through the birth canal. “This trade-off explains why we have such helpless infants, but also very painful and long births,” says Nicole Webb, a paleoanthropologist at the University of Tübingen and the University of Zurich.
The logic is compelling, sure, and ...
