The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Trunk modularity in recent human populations: a preliminary look at rib and pelvis covariation


Department of Anthropology, Center for the Study of Human Origins, New York University, New York Consortium in Evolutionary Primatology

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The evolution of hominin body form remains a central issue in paleoanthropology. Recent work has shifted from studies of individual skeletal elements to investigating higher-level relationships within the body using a modular framework. Few studies, however, focus on the trunk skeleton, even though this region is subject to various functional, obstetric, and energetic selective pressures. I present results from a pilot study investigating trunk modularity in three recent human populations (European- and African-Americans from the Hamann-Todd Collection and AmerIndians from the Indian Knoll Collection) using three-dimensional morphometric data on ribs and articulated pelves from adult individuals collected using a Microscribe G2X digitizer (n=132). All analyses were performed in MorphoJ. Matrix permutation tests reveal a higher magnitude of integration between rib 4 and rib 7 in the AmerIndian (0.968) and African-American (0.945) samples than in the European-American sample (0.865), with all correlations significant at p<0.01. Two-block partial least squares analyses confirm the strong relationship between the thorax elements and also suggest that elements within the thorax are more strongly integrated with each other than each are independently with the pelvis (e.g., rib4-rib7 CV=0.43 while rib7-pelvis CV=0.17), while also revealing additional population differences in the magnitude of covariation. These results suggest a degree of modularity in human trunk proportions, which may translate into greater independence in responding to selective pressures, an advantageous condition for a species with a worldwide distribution.

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