The patterning and determinants of craniofacial robusticity in extant Homo sapiens

Skeletal superstructure characteristics such as thick cranial vaults and well-developed supraorbital, infraorbital, zygomatic, temporal, and nuchal regions in hominins are collectively referred to as aspects of craniofacial robusticity. A better understanding of craniofacial robusticity is important because these features are regularly employed as individual traits in circumscribing fossil hominins as a means to separate other taxonomic groups from modern Homo sapiens even though the developmental and functional underpinnings of such traits are incompletely understood. The work of some researchers suggests that these features may be tied to a broader "robusticity complex", in which the expression of all the classically "robust" characteristics of the hominin cranium are intercorrelated and intrinsically linked. If true, then previous studies that have focused on characteristics of craniofacial robusticity as individual characters could be flawed.

This study tests for the presence of an intercorrelated craniofacial robusticity complex in a geographically diverse sample of recent Homo sapiens using a morphological integration framework. Within this framework, significant levels of correlation between features of craniofacial robusticity are demonstrative of integration and thus a "robusticity complex", while non-significant levels of correlation provide evidence for modularity and therefore an independent expression of these traits. Craniofacial robusticity is examined among four anatomical areas of the human cranium including the frontal, zygomaxillary, temporal, and occipital regions. The expression of robusticity among these anatomical regions is quantified using three-dimensional coordinate landmark data in addition to classical discrete measures and is analyzed via two-block partial least squares regression analysis.

The results show that levels of interaction between these major anatomical units are characterized by a range of correlation values with most obtaining statistical significance. These results frequently provide evidence for integration between subunits demonstrating at least partial evidence for a "robusticity complex" in the craniofacial skeleton of extant humans.