The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


The magnitude of covariation among regions of the human cranium

ALLISON NESBITT1 and KAREN L. BAAB2.

1Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 2Department of Anatomy, Midwestern University

March 27, 2015 , Archview Ballroom Add to calendar

The study of morphological integration characterizes the pattern and magnitude of morphological trait covariance. The magnitude of integration may influence evolution in that high integration may constrain the direction of morphological change, thereby maintaining correlated evolution of morphological traits, whereas weak integration may enable mosaic evolution. However, many studies of cranial integration describe the magnitude of integration as “high” or “low,” but there is no standard for how these terms are defined.

In order to assess whether the face and dentition of humans are highly integrated, it is necessary to establish a baseline of “high” and “low” integration within the human cranium. We hypothesized that regions of the cranium that are spatially, functionally or developmentally related (e.g., the upper and lower face) would exhibit higher integration than regions that are more functionally and developmentally distinct (e.g., the occipital and lower face). 3D cranial and dental landmarks were acquired from CT scans of adult human crania (n=35) and analyzed using partial least squares analysis. Covariation among the upper face, lower face, occipital bone and dentition was quantified using the RV coefficient, a measure of the strength of multivariate integration. In agreement with the hypothesis, the highest magnitude of integration was between the upper and lower face while the occipital and face displayed lower, non-significant RV coefficients. Based on this baseline, the lower face and dentition are highly integrated structures. Broader application of this approach can provide context for the evaluation of the magnitudes of integration among regions of a single structure.