The fossil evidence for the evolution of human infant helplessness, complicated labor and big babies (335.3)

The human fossil record is much richer today than it was when the obstetrical dilemma was first proposed to explain the conflicting selective constraints that result when bipeds give birth to large‐brained babies. An analysis of the morphology of several important discoveries of fossilized pelvic material from Gona in Ethiopia and Malapa in South Africa, demonstrate that a broad pelvis such as characterizes humans today did not result from expansion of the birth canal that coincided with encephalization during the last two million years, but was the primitive condition for hominins, existing in australopithecines, Homo erectus and all later humans. However, encephalization did select for further changes in the pelvis as well as changes in infant development and parental behavior. The complicated way that humans give birth and the maturational status of neonates are a result of that evolutionary history and the resulting constraints that include: bipedalism, our large brained newborns, the large size of those newborns relative to the size of the mothers who give birth to them, the helpless state in which these large babies arrive and the prolonged period of infant dependency. This expanded fossil record has implications for an understanding of the way we give birth and care for our newborn infants.