Letter

Nature 450, 1075-1078 (13 December 2007) | doi:10.1038/nature06342; Received 21 June 2007; Accepted 3 October 2007

There is a Corrigendum (5 July 2012) associated with this document.

Fetal load and the evolution of lumbar lordosis in bipedal hominins

Katherine K. Whitcome1, Liza J. Shapiro2 & Daniel E. Lieberman1

  1. Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, Massachusetts 02138, USA
  2. Department of Anthropology, University of Texas at Austin, 1 University Station, Austin, Texas 78712, USA

Correspondence to: Katherine K. Whitcome1 Correspondence and requests for materials should be addressed to K.K.W. (Email: whitcome@fas.harvard.edu).

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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