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Computer Simulations Show That Neanderthal Facial Morphology Represents Adaptation to Cold and High Energy Demands, but Not Heavy Biting

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Computer Simulations Show That Neanderthal Facial Morphology Represents Adaptation to Cold and High Energy Demands, but Not Heavy Biting

Stephen Wroe et al. Proc Biol Sci.

Abstract

Three adaptive hypotheses have been forwarded to explain the distinctive Neanderthal face: (i) an improved ability to accommodate high anterior bite forces, (ii) more effective conditioning of cold and/or dry air and, (iii) adaptation to facilitate greater ventilatory demands. We test these hypotheses using three-dimensional models of Neanderthals, modern humans, and a close outgroup (Homo heidelbergensis), applying finite-element analysis (FEA) and computational fluid dynamics (CFD). This is the most comprehensive application of either approach applied to date and the first to include both. FEA reveals few differences between H. heidelbergensis, modern humans, and Neanderthals in their capacities to sustain high anterior tooth loadings. CFD shows that the nasal cavities of Neanderthals and especially modern humans condition air more efficiently than does that of H. heidelbergensis, suggesting that both evolved to better withstand cold and/or dry climates than less derived Homo We further find that Neanderthals could move considerably more air through the nasal pathway than could H. heidelbergensis or modern humans, consistent with the propositions that, relative to our outgroup Homo, Neanderthal facial morphology evolved to reflect improved capacities to better condition cold, dry air, and, to move greater air volumes in response to higher energetic requirements.

Keywords: Homo heidelbergensis; Homo neanderthalensis; computational fluid dynamics; finite-element analysis.

Conflict of interest statement

We declare we have no competing interests.

Figures

Figure 1.
Figure 1.
La Chapelle-aux-Saints 1 Neanderthal mesh-mesh metric comparison of initial fossil material (a) with final reconstruction, (b) (performed in Cloud Compare). The models are superimposed (c) and the original-reconstructed mesh-mesh metrics are computed. (d) Regions where the final reconstruction lies further out (from the model centroid) than the original fossil material are shown in blue. Regions where the final reconstruction lies further in (from the model centroid) than the original fossil material are shown in red. Regions of the original fossil material that lie further than ±1.875 mm (3 voxel edge lengths) from the final reconstruction have been clipped from the image. Regions that overlap almost exactly are shown in off-white.
Figure 2.
Figure 2.
Results of finite-element analysis under an anterior bite simulation (loading via muscle force scaled to volume2/3, restraints applied to incisors and canines) for 10 recent (a–j) and one Pleistocene (k) modern human, as well as H. heidelbergensis (l), and three H. neanderthalensis (m–o). Number of elements for each models also given for: (a) Khoe-San female, 1 571 213, (b) Caucasian male, 1 602 686, (c) European female, 1 651 738, (d) Chinese male, 1 593 342, (e) Malay female, 1 608 934, (f) Inuit male, 1 625 463, (g) Inuit female, 1 700 708, (h) Pacific Islander male, 1 701 642, (i) Peruvian female, 1 619 268, (j) European male, 1 651 945, (k) Mladeč 1, 1 724 664, (l) Broken Hill 1, 1 611 994, (m) La Ferrassie 1, 1 618 373, (n) La Chapelle-aux-Saints 1, 1 625 022, and (o) Gibraltar 1, 1 609 723.
Figure 3.
Figure 3.
Heat flow through the left nasal passage of a (a) Homo heidelbergensis, (b) Homo neanderthalensis, and (c) Homo sapiens (UNC002). (d) Homo sapiens (ULAC210). (e) Homo sapiens (UNC013). Heat transfer is shown in cross sections taken at numbered regions in each nasal passage, and shown under both 100 ml s−1 and the mass-dependent flow rate.

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