Metabolic demands and sexual dimorphism in human nasal morphology: A test of the respiratory-energetics hypothesis

Objectives: Although ecogeographic variation in human nasal morphology is commonly attributed to climatic adaptation, recent research into the “respiratory-energetics hypothesis” has suggested that metabolic demands for oxygen intake may influence overall nasal size. Here, we further test the respiratory-energetics hypothesis and investigate potential interactions between metabolic and climatic pressures on human nasal morphology. Materials and Methods: This study employed computed tomography (CT) scans of 79 mixed-sex crania derived from an extreme cold-dry locale (Point Hope, Alaska). In conjunction with basal metabolic rate (BMR, kcal/day) estimates derived from associated femoral head diameter measurements, 41 cranial three-dimensional (3D) coordinate landmarks and 17 linear measurements were employed in multivariate analyses to test for associations between metabolic demands and nasal/facial morphology across and within the sexes. Results: Overall nasal size was found to be significantly correlated with BMR both across and within the sexes, with higher metabolic demands predictably associated with larger noses. However, associations between BMR and overall nasal size were found to be predominantly driven by nasal passage height and length dimensions, with the Arctic sample exhibiting minimal (non-dimorphic) variation in nasal passage breadths. Accordingly, significant correlations between BMR and 3D nasal shape were also identified. Discussion: Our study provides additional support for the respiratory-energetics hypothesis, while providing insights into potential metabolic and climatic constraints on specific nasal dimensions. In particular, our results suggest that climatic pressures on nasal passage breadths for heat/moisture transfers may necessitate compensatory changes in passage heights (and developmentally-linked lengths) to maintain sufficient air intake to meet metabolic requirements.