Eco-Geographical Variation in Craniofacial Size and Shape, With Emphasis in Cold Adaptation, Through a 3D Approach

Introduction

This study examines cranial morphological variations across populations adapted to different climates, with a focus on cold adaptation. Using a 3D geometric morphometric approach, the study analyzes skull variability between populations from various latitudes and climates. Two null hypotheses are tested: (1) differences in skull size and shape are unrelated to climate, and (2) no differences exist between populations with recent versus ancient cold adaptation.

Material and Methods

Skulls from five populations across different climates were analyzed using 3D geometric morphometrics. Landmarks were digitized, and statistical analyses were performed to evaluate size and shape variations among the populations.

Results

One-way ANOVA Bonferroni post hoc analysis revealed significant size differences. Norsemen differed significantly from all other samples, except Sub-Saharan Africans. Cold-adapted populations exhibited larger skull sizes, whereas populations from mild and hot climates had smaller skulls. However, Norsemen exhibited unexpectedly smaller sizes. Notable anatomical disparities are observed along both PCs. PC1+ showed increased prognathism and wider faces in Southern Patagonia and Greenland Thule. PC2+ highlighted larger faces and sloping foreheads in Southern Patagonia and European populations. Median shape analysis reveals pronounced prognathism and wider skulls in Southern Patagonia, with Greenland Thule showing similar traits but with a more globular braincase.

Conclusion

Notable craniofacial similarities associated with extreme cold adaptation, including increased prognathism, prominent glabellar and supraciliary regions, lateral zygomatic expansion, enlarged nasal cavity and orbits, and elongated, flattened braincase, despite genetic differences. However, the Norse sample presents a deviation from expected patterns, exhibiting smaller sizes despite inhabiting a cold region.