A Long-Standing Theory of Childbirth Is a Myth

As billions of people can attest, giving birth is hard for humans. Our infants have an exceptionally large head for their body size and yet have to squeeze through a very narrow pelvis. Appendages can get stuck; bones can fracture. At worst, the consequences can be lethal for mothers or babies. Until recently, many researchers believed that our species weathered that particular hardship alone: Other primates, they supposed, didn’t need to strike the same compromise between super-brains and walking upright, and so could birth babies with relative ease. But new evidence has started to challenge the notion that human childbirth is uniquely dangerous.A new paper published today in Nature Ecology & Evolution offers one of the most compelling cases to date against that assumption—showing that other primates, too, must push their babies through some seriously restricted spaces, contributing to infant-death rates that can exceed 34 percent. Humans have long put ourselves on an evolutionary pedestal—“We always think we are special,” Nicole Webb, an evolutionary biologist at the Senckenberg Research Institute and Natural History Museum, in Germany, who wasn’t involved in the new research, told me. But the more scientists have looked across the animal kingdom, the more the biological realities of other animals have upended this narrative.The assumption that people have it especially rough during childbirth can largely be traced back to a scientist named Adolph Schultz. Schultz’s research was revolutionary: Nearly a century ago, he was the first to gather evidence on the pelvic proportions of several primate species as a proxy for how easily their babies would fit. But his approach also had serious flaws, Nicole Torres-Tamayo, an anthropologist at the Miquel Crusafont Catalan Institute of Paleontology, in Spain, and one of the new study’s authors, told me. Schultz was wrong about the orientation in which the fetal head of different primates moved through the birth canal. He als