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Morphological variation of the modern human sacrum with implications for early hominins

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author FornaiC, NüeschM, KrennV, HaeuslerM,
Project Birth and human evolution - implications from computer-assisted reconstructions
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Original article (peer-reviewed)

Journal American Journal of Physical Anthropology
Volume (Issue) 165(S66)
Page(s) 87 - 88
Title of proceedings American Journal of Physical Anthropology

Open Access

Type of Open Access Publisher (Gold Open Access)


Owing to its central role in childbirth, the human pelvis shows marked sexual dimorphism. The degree of pelvic morphological heterogeneity in relation to body size and ancestry is not fully known, and the contribution of the different anatomical components to its variation, particularly throughout human evolution, is unexplored. The female sacrum is typically described as broader, shorter, and more curved than in males, contributing to a pelvic canal configuration more suited to birth. Early hominin sacral morphology can best be assessed in Australopithecus africanus. Sts 14, a probable female shows very wide sacral alae relative to the S1 corpus, whereas the probable male Stw 431 has relatively narrow alae. Our modern comparative sample is based on osteological and patient data from individuals with known sex and geographical origin from Central Europe, Southern Asia, and Africa, including small-bodied populations. Using geometric morphometrics, we investigated shape and size differences based on a dense configuration of landmarks and semilandmarks. Our results confirmed that length-to-width and S1 corpus-to-alae proportions best distinguish between sexes. Conversely, sacral curvature is not sexually dimorphic, although females show lower variation. High heterogeneity was detected at the sacral alae, possibly because of their moderate influence on reproductive success. Furthermore, regression analyses revealed that size and ancestry have negligible effect on sacral shape. Finally, we compare modern human sacral morphology with Stw 431 and Sts 14, and discuss its implications for sexual dimorphism, birth and taxonomy in these early hominins. This research was funded by the Swiss National Science Foundation grants No 31003A_156299/1 and 31003A_176319, the Mäxi foundation, and the Swiss Society for Anthropology.