INVESTIGATING ECOGEOGRAPHIC VARIATION IN SUPERIOR AND FUNCTIONAL ETHMOIDAL BREADTH IN INTERNAL AIRWAY DIMENSIONS

Superior Ethmoidal Breadth (SEB = maximum breadth between the left and right frontoethmoidal sutures) is widely employed as a proxy for internal nasal airway dimensions. SEB is also commonly argued to evince climatic adaption in modern humans, as populations living in cold-dry environments predictably exhibit narrower SEB dimensions than those inhabiting tropical environments. However, as SEB anatomically spans the upper nasal airways (common and superior meatuses) and the ethmoid air cells, the accuracy of SEB as a proxy for airway dimensions remains questionable. Here, we evaluate the correlation between SEB and internal airway dimensions using linear measurements collected on CT scans from a mixed-sex sample of human crania (n=217) ancestrally derived from sub-Saharan Africa, Europe, East Asia, and the Arctic Circle. Our results demonstrate SEB is highly correlated (r=0.807, p< 0.0001) with functional airway breadth (FEB), suggesting SEB is a reliable proxy. ANOVA results indicate, in addition to significant differences in SEB (F=36.5, p< 0.0001), regional differences exist for common (F=3.95, p=0.009) and superior (F=3.19, p=0.024) meatus breadths and ethmoid air cell breadth (F=9.01, p< 0.0001). Specifically, the African-derived sample consistently exhibit the widest nasal dimensions and the Arctic-derived sample the narrowest dimensions. Our results indicate a positive scaling relationship between SEB and internal airway breadths, with the wider SEB values of the African-derived sample actually underestimating their disproportionately wider common and superior meatuses. Cumulatively, these results empirically support use of SEB as proxy for upper nasal airway breadth.