Anthropology, University of Iowa
Friday 26, Park Concourse
Several adaptations have been proposed to account for variations in cranial vault thickness between populations of recent Homo sapiens, and between Homo species, including protection from interpersonal violence, and masticatory strain. The protection hypothesis states that codified interpersonal violence, in the form of ritualized, face-to-face dispute settlement, would result in increased bone thickness on the anterior vault. This hypothesis is mainly applied to Native Australians. The strain hypothesis states that vault thickness would co-vary with the intensity of masticatory forces, based on the placement and orientation of muscle attachments on the vault. In this study, I compare thickness of the frontal bone versus the parietal bones for 9 populations of recent H. sapiens to assess whether Australians have uniquely greater frontal thickness. Also, I will compare patterns of thicker and thinner bone with patterns of vault strain to determine any relationship of thickening to buttress against strain. I find that Australians are not the only population with thicker frontals than parietals, which does not support an adaptive interpretation specific to Australians. When comparing locations of strain to thickened vault regions, 26% of the sample had thickening in the midsagittal plane, the plane along which nuchal muscle strain radiates, while masticatory strain registers in the coronal plane, along the coronal suture, a location that does not seem to show increased thickness in this sample. These hypotheses are refuted. For cranial vault thickness, “thick” versus “thin” is an over-simplification. There are complex patterns of variation within individuals and the entire species.
This research was funded by a Sigma Xi Grant-In-Aid of Research, and by the University of Iowa Graduate College and Athropology Department.