Edited by Cynthia M. Beall, Case Western Reserve University, Cleveland, OH, and approved July 31, 2017 (received for review March 13, 2017)
Due to its role in humidifying and warming the air before it reaches the lungs, adaptations in the internal nasal anatomy are suspected to have been essential for modern humans and Neanderthals during the settlement of Eurasian harsh landscapes. Unfortunately, the lack of soft-tissue evidence in the fossil record precludes any study of Neanderthal respiratory performance. Here, we use warping techniques to reconstruct a generic Neanderthal nose, computational fluid dynamics simulations to compare the respiratory performance on both species, and evolutionary analyses to detect signals of selection. We report striking differences on fluid residence times under cold/dry climatic conditions. Different from previously suggested, our results indicate that both species would have achieved an advantageous species-specific respiratory performance in cold climates.
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.
↵1S.d.A., M.F.G., and C.C. contributed equally to this work.
Author contributions: S.d.A., M.F.G., C.C., O.V., R.R.P., and R.G.-J. designed research; S.d.A., M.F.G., C.C., V.R., M.Q.-S., F.M., T.H., C.P., A.R., P.N., B.A.P., C.C.S.d.C., O.V., F.R.-R., N.C., H.G.C., R.R.P., and R.G.-J. performed research; O.V., F.R.-R., H.G.C., R.R.P., and R.G.-J. contributed new reagents/analytic tools; S.d.A., M.F.G., C.C., V.R., M.Q.-S., F.M., T.H., C.P., A.R., P.N., B.A.P., C.C.S.d.C., O.V., F.R.-R., N.C., H.G.C., R.R.P., and R.G.-J. analyzed data; and S.d.A., C.C., F.R.-R., R.R.P., and R.G.-J. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1703790114/-/DCSupplemental.
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