Nasal airflow simulations suggest convergent adaptation in Neanderthals and modern humans

Abstract

Both modern humans (MHs) and Neanderthals successfully settled across western Eurasian cold-climate landscapes. Among the many adaptations considered as essential to survival in such landscapes, changes in the nasal morphology and/or function aimed to humidify and warm the air before it reaches the lungs are of key importance. Unfortunately, the lack of soft-tissue evidence in the fossil record turns difficult any comparative study of respiratory performance. Here, we reconstruct the internal nasal cavity of a Neanderthal plus two representatives of climatically divergent MH populations (southwestern Europeans and northeastern Asians). The reconstruction includes mucosa distribution enabling a realistic simulation of the breathing cycle in different climatic conditions via computational fluid dynamics. Striking across-specimens differences in fluid residence times affecting humidification and warming performance at the anterior tract were found under cold/dry climate simulations. Specifically, the Asian model achieves a rapid air conditioning, followed by the Neanderthals, whereas the European model attains a proper conditioning only around the medium-posterior tract. In addition, quantitative-genetic evolutionary analyses of nasal morphology provided signals of stabilizing selection for MH populations, with the removal of Arctic populations turning covariation patterns compatible with evolution by genetic drift. Both results indicate that, departing from important craniofacial differences existing among Neanderthals and MHs, an advantageous species-specific respiratory performance in cold climates may have occurred in both species. Fluid dynamics and evolutionary biology independently provided evidence of nasal evolution, suggesting that adaptive explanations regarding complex functional phenotypes require interdisciplinary approaches aimed to quantify both performance and evolutionary signals on covariation patterns.

Climatic adaptation in human inferior nasal turbinate morphology: Evidence from Arctic and equatorial populations

“…Given that clinical studies (e.g., Dayal et al, ; Li et al, ; Lindemann et al, ; Ozlugedik et al, ) have demonstrated surgical alteration of the turbinates can produce significant changes in overall heat and moisture transfer within the nose, our finding of significant regional differences in modern human turbinate morphology highlights the importance of appropriate turbinate reconstruction in airflow modeling among fossil specimens with damaged internal nasal morphology (e.g., de Azevedo et al, ; Wroe et al, ). In particular, our results suggest that variation in turbinate morphology coordinates with the encapsulating outer walls of the nasal passage to influence the functional dimensions of the nasal airways.…”

Nasal variation in relation to high‐altitude adaptations among Tibetans and Andeans

“…Along these lines, investigations into the developmental mechanisms inducing changes in nasal cavity form also need to be conducted. Several studies discuss the importance of temperature‐gradients in driving cartilaginous growth of the cranial structures (Hammer & Butaric, ; Huggins & Blockshom, ; West‐Eberhard, ) and in nasal flow/pressure specifically driving nasal form (de Azevedo et al, ). However these relationships, particularly among environments experiencing diverse levels of air pressure, are far from being fully understood.…”

Aspects of human physical and behavioural evolution during the last 1 million years

“…Alternatively, the Neanderthal nasal morphology could equally have served to accommodate increased respiratory demands (Wroe et al ., ). The capacious nasal cavities of Neanderthals and modern humans were seemingly more adept at conditioning air than those of H. heidelbergensis , and Neanderthals were able to move a greater volume of air through their nasal pathway than either H. sapiens or H. heidelbergensis (Wroe et al ., ; see also de Azevedo et al ., ). Additionally, reconstructions of the Neanderthal thorax indicate that they would have had a slightly increased respiratory capacity relative to modern humans (Gómez‐Olivencia et al ., ).…”