The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

The effects of living conditions on human cranial and postcranial sexual dimorphism


Center for Functional Anatomy & Evolution, Johns Hopkins University School of Medicine

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Previous studies suggest that environmental variables differentially affect male and female body size, resulting in decreased sexual size dimorphism in samples under stressed conditions. In comparison, research investigating the relationship between living conditions and craniofacial trait dimorphism is lacking. Given that conspicuous craniofacial traits are not as costly to maintain and play a significant role in mate preferences, craniofacial trait dimorphism may be expected to either remain constant under stressed conditions, or possibly increase due to greater sexual selection pressures.

This study tests these two hypotheses by evaluating sexual dimorphism in body size and two specific cranial traits, the browridge and chin, across an array of diverse populations (13 samples, total n = 670). Genetically similar, yet environmentally varied paired samples are included to better isolate the effects of living conditions from population differences. Postcranial size dimorphism was calculated using traditional osteometric methods. In order to compare sexual dimorphism in the browridge and chin morphologies across groups, 3D surface scans were collected, and a method developed to objectively isolate the brow and chin segments. Transects and semi-landmarks were extracted from each segment for morphometric analyses. Dimorphism was calculated as the distance between male and female centroids in shape space. Results indicate that when all samples are pooled, there is a general positive relationship between body size dimorphism and craniofacial dimorphism. However, when specific paired samples are compared, only dimorphism in body size decreases in the more stressed samples, with no consistent trend in cranial trait dimorphism.

This study was funded by National Science Foundation DDIG, grant number BCS-1061313, and Sigma Xi GIAR, grant number G20101015155040.

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