Latitudinal and climatic distributions of 3D craniofacial features among Holocene populations

Abstract

The geographical and climatic patterning in craniofacial morphology among recent hominids has been regarded as relatively reliable evidence of environmental adaptation and natural selection, which is largely attributed to thermoregulation. However, the relative influence of genetic and environmental factors on craniofacial features is unclear. Our study employed 3D laser scanning techniques to evaluate the association between geographical (latitude), climatic (annual temperature) factors, and 3D craniofacial measurements in 18 recent populations through bivariate correlation analysis. Significant correlations were found among braincase surface area, zygomatic bone surface area, cranial-facial index (facial surface area relative to braincase surface area) and local temperature, and a clear latitudinal gradient was also found in variation of braincase surface area. No significant correlations were found between zygomatic bone surface area, cranial-facial index and latitude. Our analysis supports the idea that the braincase functions as a radiator and is closely related to direct sunlight. We also suggest that absolute/relative craniofacial surface area varies consistently with predictions derived from Bergmann’s Rule. The mosaic craniofacial traits of American Indians may reflect retention of cold-derived, ancestral features, as well as a response to a slightly warmer climate. Because different craniofacial regions preserve environmental/genetic signatures differentially, caution is suggested when craniofacial anatomy is used for phylogenetic reconstruction and functional-morphological analysis.