Fetal load and the evolution of lumbar lordosis in bipedal hominins.

Bibliographic Collection: 
MOCA Reference, APE
Publication Type: Journal Article
Authors: Whitcome, Katherine K; Shapiro, Liza J; Lieberman, Daniel E
Year of Publication: 2007
Journal: Nature
Volume: 450
Issue: 7172
Pagination: 1075-8
Date Published: 2007 Dec 13
Publication Language: eng
ISSN: 1476-4687
Keywords: Animals, Biological Evolution, Female, Fetal Weight, Hominidae, Humans, Lumbar Vertebrae, Lumbosacral Region, Male, Pan troglodytes, Pregnancy, Sex Characteristics, Walking

As predicted by Darwin, bipedal posture and locomotion are key distinguishing features of the earliest known hominins. Hominin axial skeletons show many derived adaptations for bipedalism, including an elongated lumbar region, both in the number of vertebrae and their lengths, as well as a marked posterior concavity of wedged lumbar vertebrae, known as a lordosis. The lordosis stabilizes the upper body over the lower limbs in bipeds by positioning the trunk's centre of mass (COM) above the hips. However, bipedalism poses a unique challenge to pregnant females because the changing body shape and the extra mass associated with pregnancy shift the trunk's COM anterior to the hips. Here we show that human females have evolved a derived curvature and reinforcement of the lumbar vertebrae to compensate for this bipedal obstetric load. Similarly dimorphic morphologies in fossil vertebrae of Australopithecus suggest that this adaptation to fetal load preceded the evolution of Homo.

DOI: 10.1038/nature06342
Alternate Journal: Nature
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