Anatomical Adaptation to Climate: Patterns of Covariation Between Brain and Nasal Morphology

Anatomical adaptation to climate: Patterns of covariation between brain and nasal morphology Jonathan Pineda* & Scott D. Maddux, Ph.D.** *TCOM, **Center for Anatomical Sciences, Dept. of Physiology and Anatomy, UNTHSC PURPOSE: Previous research has shown that the geographic distributions of both brain and nasal shape are highly correlated with climatic variables. Specifically, individuals indigenous to cold-dry environments typically exhibit relatively wider brains (for retention of heat), and taller/longer/narrower nasal passages (for enhanced warming and humidification of respired air) compared to individuals from hot-humid climates. While these ecogeographic patterns of brain and nasal shape are both well established, the spatial interaction of these two structures in relation to climate has not been as rigorously investigated. METHODS: We employed CT scan data collected from a total of 30 human crania from the Arctic Circle (9 female, 6 male) and West Africa (8 female, 7 male). 3D digital models were subsequently rendered for each cranium using the 3D Slicer software program and a total of 35 craniofacial landmarks were then placed on each 3D model, permitting assessment of both linear measurements (i.e., Euclidean distances) and 3D spatial relationships via univariate and multivariate statistical analyses. RESULTS: Largely consistent with previous research, permutational t-test results indicate that individuals from the Arctic Circle possess shorter (p=0.029) and wider (p=0.002) braincases compared to West Africans. Similarly, Arctic natives were also found to possess both taller (p=0.0001) and narrower (p=0.001) nasal passages. While on average the Arctic sample also possessed a longer nasal passage (69.8 mm) compared to the Africans (67.1 mm), this difference was not statistically significant (p=0.097). Moreover, a simultaneous-fit two-block partial least squares (2B-PLS) analysis of 3D coordinate landmarks, reveals a significant pattern of covariation (RV=0.37, p=0.012) between nasal and brain morphology, with the first PLS dimension (46.3% of the total covariation) reflecting a significant association between relative brain width and nasal height, width, and length (r=0.74, p=0.032). CONCLUSIONS: Cumulatively, these results are consistent with previous studies, and support the hypothesis that climate has simultaneously influenced both brain and nasal anatomy. Moreover, our 2B-PLS results suggest that the relative spatial positioning of the nose may actually contribute to overall brain thermoregulation by differentially influencing airflow under the basicranium in different climatic regimes.