Human babies barely fit through the birth canal. In the U.S. alone, 700 people die each year from complications during delivery. 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 the smoking gun could be out there. Webb’s team is searching for it as we speak. But others, like Holly Dunsworth, a bioanthropologist at the University of Rhode Island, says there’s not much evidence to support this. “People tend to get swept away by good stories,” she says. “But the obstetrical dilemma is an untrue way of evolution occurring.”
