Covariation patterns and respiratory simulation in modern human and Neanderthal noses

Abstract

It is likely that a proper respiratory performance on cold and dry climates was an adaptive pre-requisite to the human settlement of Eurasian landscapes during the last Glacial Maximum. Research on covariation patterns among different anatomical parts of the nasal tract is of key importance to simulate the respiratory performance under several conditions. Data on covariation among soft versus hard tissues, or vestibular versus nasopharyngeal structures, for instance, is necessary to obtain a proper in silico reconstruction of the internal nasal tract. Here we present an extensive covariation analysis of nasal tracts including human and non-human primates as well as hard and soft tissues obtained via Computed Tomography. Furthermore, we used warping techniques to reconstruct three complete nasal tracts corresponding to two modern human populations evolved on temperate (southern European) and cold-dry (eastern Asian) climates, and a generic Neanderthal nose. Reconstructed noses including the mucosa surface were submitted to Computational Fluid Dynamics (CFD) in order to simulate respiratory regimes and climatic conditions. Simulations revealed that across-individuals differences in fluid residence time significantly affect nasal humidification and warming dynamics. Under cold/dry climatic regimes, the eastern Asian model achieved the most rapid conditioning at the vestibular region, followed with slightly less rapid conditioning by the Neanderthal model. In contrast, the southern European model reached a physiologically satisfactory conditioning less rapidly, around the medium-posterior nasal tract. These CFD results suggest that proper air conditioning is attained in some human groups and Neanderthal nasal tracts despite significant among-taxa craniofacial differences.