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Fetal load and the evolution of lumbar lordosis in bipedal hominins

A Corrigendum to this article was published on 30 May 2012


As predicted by Darwin1, bipedal posture and locomotion are key distinguishing features of the earliest known hominins2,3. 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 lordosis4,5,6. 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.

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Figure 1: COM and lumbar lordosis during pregnancy.
Figure 2: Maternal COM and lumbar lordosis relative to fetal load.
Figure 3: Sex differences in the lumbar vertebral column of human males and females.
Figure 4: Australopithecine lumbar lordosis and prezygapophyseal angle.

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We thank W. Sanders for fossil measurements and discussion; S. Ford, J. Jensen, J. Kappelman, D. Overdorff, D. Pilbeam, D. Raichlen, P. Rightmire and C. Ruff for comments and assistance with research; L. Gordon, D. Hunt, L. Jellema, B. Latimer and R. Thorington for access to specimens; and the Developmental Motor Control Laboratory at the University of Texas, Austin, for laboratory use. Figure 1 was drawn by L. Meszoly. This work was supported by grants from the National Science Foundation (to L.J.S. and K.K.W.), the L. S. B. Leakey Foundation (to K.K.W.), the National Science Foundation (to D.E.L.) and the American School of Prehistoric Research (Harvard).

Author Contributions K.K.W. designed the study, conducted the experiments, and analysed and interpreted the data. L.J.S. assisted in the study design and the interpretation of results. D.E.L. assisted in the fossil study design and in the analysis and interpretation of the fossil and biomechanical data. K.K.W., L.J.S. and D.E.L. wrote the manuscript.

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Correspondence to Katherine K. Whitcome.

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Whitcome, K., Shapiro, L. & Lieberman, D. Fetal load and the evolution of lumbar lordosis in bipedal hominins. Nature 450, 1075–1078 (2007).

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