Investigating ecogeographic variation in superior and functional ethmoidal breadth in internal nasal dimensions
Grace, Caroline Reid
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Superior Ethmoidal Breadth (SEB = the maximum breadth between the left and right frontoethmoidal sutures) has been widely employed by anthropologists as a proxy for internal nasal airway dimensions since it is easily measured without imaging. 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, given uncertaintiy regarding its relationship with internal nasal anatomy, the accuracy of SEB as a proxy for airway dimensions remains questionable. Here, I 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=215) ancestrally derived from sub-Saharan Africa, the Arctic Circle, East Asia, and Europe. My results demonstrate that SEB is often located superior to the anatomcial roof of the nasal passages but is highly correlated (R= 0.8119, p<0.0001) with ethmoidal breadth taken at the functional level of the upper airways (i.e., functional airway breadth [FEB]). ANOVA results indicate, in addition to significant differences in SEB (χ2 = 82.20, p<0.0001), regional differences also exist for FEB (χ2 = 54.21, p<0.0001) and its components: the combined superior and superior common meatal breadths (χ2 = 19.03, p< 0.0001) and ethmoid air cell (EAC) breadth (χ2 = 27.67, p<0.0001). Further, following theoretrical expecations, the African-derived sample generally exhibits the widest internal nasal dimensions and the Arctic-derived sample the narrowest. Specifically, the Arctic sample exhibits significantly narrower airway breadths compared to all other groups. Conversely, the African sample possesses significantly wider EAC breadths comapred to all other groups. Cumulatively, these results empirically support use of SEB as proxy for upper nasal airway breadth and bolster claims that clinal variation in internal airway dimensions across human populations is likely attributable to climatic factors.