Mechanism of birth in chimpanzees: humans are not unique among primates

Researchers have argued that the process of human birth is unique among primates and mammals in that the infant emerges with its face oriented in the opposite direction from its mother (occiput anterior) and head rotation occurs in the birth canal. However, this notion of human uniqueness has not been substantiated, because there are few comparative studies of birth in non-human primates. This paper reports the mechanism of birth in chimpanzees (Pan troglodytes) based on the first clear, close-up video recordings of three chimpanzee births in captivity. In all three cases, the foetus emerged with an occiput anterior orientation, and the head and body rotated after the head had emerged. Therefore, these characteristics are not uniquely human. Furthermore, in two of the three cases, the chimpanzee newborns landed on the ground without being guided from the birth canal by the mother. The fact that the human newborn emerges with an occiput anterior orientation has thus far been taken as evidence for the necessity of midwifery in modern humans, but this view also needs revision. Our observations raise the need to reconsider the evolutionary scenario of human birth.