¹Department of Archaeology and Anthropology, University of Cambridge, ²Department of Anthropology, University of Michigan, ³McDonald Institute for Archaeological Research, University of Cambridge

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Analyses of archaeological human remains and modern athletes have demonstrated a correspondence between levels of directional asymmetry in upper limb bone diaphyses and lateralized limb function. In humans, greater diaphyseal rigidity in the dominant limb is common. The first study of long bone bilateral asymmetry among chimpanzees (Sarringhaus et al., 2005) identified a different pattern: approximately 70% of adults featured more rigid right hand second metacarpal diaphyses, while a similar proportion of individuals displayed more rigid left humeri. This likely reflects the differing influences of both manipulatory and postural behaviour on chimpanzee skeletal structure. The current study demonstrates a consistent pattern of greater mid-diaphyseal rigidity in the right upper limb bones among a wide range of human populations. While right hand dominance appears to be characteristic of all populations, between 17 and 37% of individuals within populations show more robust diaphyses of one or more left elements. To investigate interspecific patterns of asymmetry, we used 3D laser scanning to estimate bone rigidity at 1% intervals along the diaphyses of clavicles, humeri, ulnae and radii for Pan troglodytes, Gorilla gorilla, Pongo pygmaeus, and Homo sapiens. The results suggest that within humans, a pattern of consistent directional asymmetry exists throughout the limb. The limbs of Gorillas show the lowest levels of bilateral asymmetry, while Pan and Pongo have greater and more variable directional asymmetry throughout the limb. This demonstrates that whole limb patterns of asymmetry differ between species, and appear to be influenced by activity and locomotion.

This research was funded, in part, by a grant from the Natural Environment Research Council, U.K.