As humans parted evolutionary ways with our primate cousins over millennia, our pelvises got smaller while our heads got bigger. These are just two aspects of human anatomy, but they have outsize impacts on childbirth. For the last few decades, this evolutionary hypothesis of childbirth, called the obstetrical dilemma, has provided a framework for understanding how and why childbirth—which seems like it should unfurl as an instinctual, straightforward process—has become so complex.
