Center for the Study of Human Origins, Department of Anthropology, New York University, New York Consortium in Evolutionary Primatology
April 16, 2016 3:30, A 706/707
Recent modern humans are characterized by low magnitudes of integration (MI; covariation) in the cranial base. Low MIs are thought to have contributed to the evolution of modern human craniofacial anatomies. However, the correlates of MI remain largely unexplored. Multiple authors have posited that brain size, facial size, and masticatory robusticity may play a role, due to interactions between these craniofacial regions. I tested MI in the cranial base of seven primate genera including lorises, galagos, indriids, lemurs, and siamangs (n=499). These taxa represent a variety of locomotor behaviors, brain sizes, and diets. My results indicate that MI in the cranial base is linked to the height of the cranial vault relative to the length of the vault (R2=0.610, p=0.038), such that taxa with relatively taller vaults display reduced integration. MI is also linked to the proportion of overall cranial length accounted for by the cranial base (R2=0.608, p=0.039), such that taxa with relatively longer cranial bases display reduced MI. Postorbital constriction (R2=0.468) and mandibular robusticity (R2=0.457) may also be linked to MI across taxa, but relative vault volume (R2=0.001), a proxy for brain size, is not. Within strepsirrhines, overall cranial size may also play a role (R2=0.581), suggesting multiple compounding factors are involved in MI. These results suggest that, in hominins, highly reduced MI was tied to the appearance of more globular vault morphologies and not to large brain sizes themselves, and likely emerged in the direct ancestors of Homo sapiens prior to facial reduction.
Grant support for data collection was provided by the Wenner-Gren Foundation and by the Ranieri International Scholars Fund at New York University.