This is a careful study of obstetrical mechanics in monkeys, apes, and extinct hominids in order to understand the present crisis in human reproduction. Current obstetrical problems have an anthropological origin. Cesarean section, almost unknown at the beginning of the century, is now considered necessary in more than 25% of deliveries. By studying the evolution of anatomical structures and the mode of delivery among other primates, strong reasons are apparent for the present crisis in human labor and delivery. This unique study points the way to further evolution of the human birth process.