Fetal load and the evolution of lumbar lordosis in bipedal hominins

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 po...

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Bibliographic Details
Published in:Nature 2007-12, Vol.450 (7172), p.1075-1078
Main Authors: Shapiro, Liza J, Lieberman, Daniel E, Whitcome, Katherine K
Format: Article
Language:English
Subjects:
Adaptation
Animals
Biological Evolution
Earth sciences
Earth, ocean, space
Evolutionary biology
Exact sciences and technology
Female
Females
Fetal Weight - physiology
Hominidae - anatomy & histology
Hominidae - physiology
Hominids
Humanities and Social Sciences
Humans
letter
Lumbar Vertebrae - anatomy & histology
Lumbar Vertebrae - physiology
Lumbosacral Region - anatomy & histology
Lumbosacral Region - physiology
Male
multidisciplinary
Paleontology
Pan troglodytes - anatomy & histology
Pan troglodytes - physiology
Posture
Pregnancy
Pregnancy - physiology
Science
Science (multidisciplinary)
Sex Characteristics
Skeletal system
Spine
Vertebrate paleontology
Walking
Women
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Summary: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.
ISSN:0028-0836
1476-4687
1476-4679
DOI:10.1038/nature06342