Human Adaptation to Tropic Environments: A Comparison of West African and Melanesian Nasal Morphology
Authors: Cooper Amber R. , Maddux Scott D. 
Published: April 2020

It is generally accepted that humans indigenous to hot‐humid equatorial environments exhibit superoinferiorly shorter, mediolaterally wider, and more anteroposteriorly attenuated nasal passages compared to counterparts from colder and/or drier environments. This relatively short/wide/attenuated morphology has been argued to functionally minimize nasal airflow resistance in tropical environments that require little intranasal air‐conditioning (i.e., exchange of heat and moisture transfers between nasal mucosa and respired air), and/or to facilitate increased respiratory heat‐shedding in high humidity environments where sweating is a less effective thermoregulatory mechanism. However, studies of climatic adaptation in human nasal morphology have often employed West Africans as representative of all equatorial populations. Yet, the assumption that West African nasal morphology is actually comparable to non‐African equatorial populations has not been firmly established. In order to test this hypothesis, 68 three‐dimensional biometric landmarks of the nasal cavity and surrounding cranium were collected from CT scans of mixed‐sexed samples of modern humans from West Africa (n=14) and Papua New Guinea (n=17). Data were also collected on crania from the Arctic Circle (n=17) to serve as a non‐equatorial comparator. A total of 45 linear measurements were subsequently calculated from these landmark data using the Euclidean distance formula. Multivariate Analyses of Variance (MANOVA) was subsequently conducted to test for regional differences while accounting for the potential influence of sexual dimorphism. MANOVA results indicate significant differences in nasal morphology between the three regional samples (Wilk’s λ = 0.008, p = 0.012) with no evidence of significant sexual dimorphism (Wilk’s λ = 0.111, p = 0.104) or region‐sex interactions (Wilk’s λ = 0.023, p = 0.122). Results of subsequent univariate ANOVAs for each linear measurement indicate no significant differences between any of the three samples for dimensions of the nasopharynx. However, the Arctic sample was found to exhibit significant differences in nasal cavity height, length, and especially breadth compared to both the West African and Papua New Guinea samples. Conversely, the two equatorial samples were only found to exhibit a significant difference for a single variable (nasal aperture breadth), with the West African sample possessing significantly wider apertures. Overall, these results suggest that equatorial populations generally exhibit similar nasal morphologies, which are likely adaptive for breathing in hot‐humid environments. Still, additional research across larger and more diverse samples of equatorial humans is needed, especially to more rigorously evaluate the degree of variation in nasal aperture breadth among populations from tropical environments. Future investigations incorporating genetically related populations which inhabit different climates (e.g., Papua New Guinea and Australia) could also further clarify the role of climate in shaping ecogeographic variation in nasal morphology.

Support or Funding Information

Funding was provided by the American Association for Anatomy Innovations Program.