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The acquisition of human verticality with an emphasis on sagittal balance

Type of publication Peer-reviewed
Publikationsform Contribution to book (peer-reviewed)
Author TardieuChristine, HaeuslerMartin,
Project Birth and human evolution - implications from computer-assisted reconstructions
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Contribution to book (peer-reviewed)

Book 9781626237322
Editor , Labelle Hubert; , Gehrchen Martin; , Pinheiro-Franco João Luiz ; , Roussouly Pierre
Publisher Thieme, New York
Page(s) 13 - 22
ISBN 9781626237322
Title of proceedings 9781626237322

Open Access

URL www.zora.uzh.ch
Type of Open Access Repository (Green Open Access)

Abstract

The shift from facultative to permanent bipedalism was a pivotal step in human evolution. Skeletal adaptations to efficient sagittal balance of the trunk are therefore key to identify fossils as our ancestors, the hominids. Morphological modifications of the pelvis and spine had a major role in this process. Here, we review these evolutionary adaptations that resulted in the formation of the spinopelvic functional unit. We suggest that the double S-shape of the vertebral column evolved secondary to the functionally linked pelvic modifi- cations. Together with the lumbar lordosis, the approximation of the sacroiliac and hip joints brought the center of body mass closer to the hip joints, thus minimizing muscular work to maintain equilibrium. A prerequisite for the adoption of lumbar lordosis in early hominids was a long and mobile lumbar spine. As great apes have a rigid spine with three to four lumbar ver- tebrae, different scenarios have been proposed for the evolution of the human spinal segmentation. We argue that the common ancestor of chimpanzees and humans already possessed five lumbar vertebrae, and a pelvic incidence of - 30 ° that increased during evolution as the sacro-acetabular distance decreased. The strong correlation in humans between pelvic incidence and lumbar lordosis points toward an elaborated functional link that was shaped by natural selection. A review of the hominid fossil record, including Sahelanthropus,Orrorin,Ardipithecus ramidus,Australopithecusafarensis,Australopithecusafricanus, Australopithecussediba, Homo erectus, and Neanderthals, suggests that this link between pelvis and spine was probably only established with H. erectus1.5 million years ago.
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