The obstetric pelvis of A.L. 288-1 (Lucy)

Abstract

Due to the fragmentary condition of most specimens, there have been few studies on the anatomy of the early hominid bony birth canal. However, recovery of an innominate and sacrum from one individual (A.L. 288-1, Australopithecus afarensis) allows reconstruction of the complete pelvis. Although A.L. 288-1 is considered to have been a female, several morphologies of its true pelvis resemble those of human males, such as sacral angulation, ischiopubic ramus and, principally, funnelling of the pelvic cavity. The implication is that some of the pelvic dimorphisms characteristic of modern Homo sapiens developed subsequent to the emergence of bipedalism. The shape of A.L. 288-l's true pelvis is compared with that of female H. sapiens and Pan troglodytes. A.L. 288-l's pelvis is platypelloid, unlike Homo and Pan. The obstetric consequence of the difference in pelvic shape would have been a unique mechanism of birth in A.L. 288-1, with the fetus being born along the transverse axis of the outlet. Rotation of the fetal cranium within the pelvic canal, a characteristic of human birth, would not have occurred in A.L. 288-1. The platypelloid (false and true) pelvis of A.L. 288-1 is related to the requirements of locomotion and visceral accommodation and support. Although the obstetric analysis indicates that birth might have been slow and difficult in A.L. 288-1, we do not consider there to have been selection for the australopithecine fetus to have been born in a more altricial state than that in pongids. However, exactly when secondary altriciality, which is a characteristic of modern humans, emerged is a current subject of debate.