Differential Scaling Patterns in Maxillary Sinus Volume and Nasal Cavity Breadth Among Modern Humans

Among modern humans, nasal cavity size and shape reflect its vital role in air conditioning processes. The ability for the nasal cavity to augment its shape, particularly in inferior breadth, likely relates to the surrounding maxillary sinuses acting as zones of accommodation. However, much is still unknown regarding how nasal and sinus morphology relate to each other and to overall craniofacial form, particularly across diverse populations with varying respiratory demands. As such, this study uses computed tomographic (CT) scans of modern human crania (N = 171) from nine different localities to investigate ecogeographic differences in (1) the interaction between maxillary sinus volume (MSV) and nasal cavity breadth (NCB) and (2) scaling patterns of MSV and NCB in relation to craniofacial size. Reduced major axis (RMA) regression reveals that all samples exhibit an inverse relationship between MSV and NCB, but statistical significance and the strength of that relationship is sample dependent. Individuals from cold-dry climates have larger MSVs with narrower NCBs, while smaller MSVs are associated with wider NCBs in hot-humid climates. MSV and NCB each scale with positive allometry relative to overall craniofacial size. However, sample differences are evident in the both the interaction between MSV and NCB, as well as their correlation with craniofacial size. While these results provide further support that the maxillary sinus and nasal cavity are integrated among populations from opposite ends of the climatic spectrum, additional epigenetic factors are needed to explain variation of these structures among populations from more intermediate climates.