Evaluating Energetic Demands on the Human Nose Within a Regional Sample

Purpose: It is widely recognized that the primary function of the nose is to warm, humidify, and filter air in preparation for entry into the lungs. Accordingly, geographic variability in nasal anatomy has long been attributed to climatic adaptation. However, as the human nose is also the primary respiratory conduit during normal breathing, it must facilitate a sufficient intake of oxygen to meet metabolic demands. Thus, given that body size also exhibits considerable geographic-mediated variation, it has long been argued that metabolism may represent a confounding influence on human nasal morphology. In particular, given its critical role in air-conditioning, it has been hypothesized nasal passage breadth should most strongly correlate with climate. Conversely, it has been suggested that nasal height and length dimensions may represent compensatory mechanisms for ensuring that a sufficient volume of oxygen can be inspired to meet body size/metabolic demands. Methods: To test these hypotheses, we obtained CT scan data for 35 modern human crania from the Bronze-Age archaeological site of Tepe Hissar, Iran. CT dicom images for each cranium were initially processed using the 3D Slicer software program, rendering a 3D digital model which was subsequently oriented in the Frankfurt Horizontal position to permit anthropometry. A total of 61 craniofacial landmarks were then placed on each 3D model, from which 15 linear measurements of nasal morphology were ultimately calculated using the Euclidean distance formula. These 15 nasal measurements were then employed in conjunction with body size/stature estimations (i.e., metabolic proxies) derived from associated post-cranial measurements, to assess the relationship between body size and nasal anatomy. Results:Following theoretical expectations, our results indicate that, within this one geographic sample (i.e., holding climate constant), no measure of nasal passage breadth was significantly correlated with body size (all p-values [greater than] 0.06). Conversely, all height and length measurements of the nasal aperture and internal cavity were found to be significantly correlated with body size (all r-values=0.48-0.62, all p-values Conclusions: Collectively, these results support the assertion that airway height and length dimensions reflect metabolic demands for sufficient intake of oxygen, while nasal breadth dimensions are more likely driven by climatic factors.