Bite force production capability and efficiency in Neandertals and modern humans

Abstract

Although there is consensus that Neandertal craniofacial morphology is unique in the genus Homo, debate continues regarding the precise anatomical basis for this uniqueness and the evolutionary mechanism that produced it. In recent years, biomechanical explanations have received the most attention. Some proponents of the "anterior dental loading hypothesis" (ADLH) maintain that Neandertal facial anatomy was an adaptive response to high-magnitude forces resulting from both masticatory and paramasticatory activity. However, while many have argued that Neandertal facial structure was well-adapted to dissipate heavy occlusal loads, few have considered, much less demonstrated, the ability of the Neandertal masticatory system to generate these presumably heavy loads. In fact, the Neandertal masticatory configuration has often been simultaneously interpreted as being disadvantageous for producing large bite forces. With rare exception, analyses that attempted to resolve this conflict were qualitative rather than quantitative. Using a three-dimensional digitizer, we recorded a sequence of points on the cranium and associated mandible of the Amud 1, La Chapelle-aux-Saints, and La Ferrassie 1 Neandertals, and a sample of early and recent modern humans (n = 29), including a subsample with heavy dental wear and documented paramasticatory behavior. From these points, we calculated measures of force-production capability (i.e., magnitudes of muscle force, bite force, and condylar reaction force), measures of force production efficiency (i.e., ratios of force magnitudes and muscle mechanical advantages), and a measure of overall size (i.e., the geometric mean of all linear craniofacial measurements taken). In contrast to the expectations set forth by the ADLH, the primary dichotomy in force-production capability was not between Neandertal and modern specimens, but rather between large (robust) and small (gracile) specimens overall. Our results further suggest that the masticatory system in the genus Homo scales such that a certain level of force-production efficiency is maintained across a considerable range of size and robusticity. Natural selection was probably not acting on Neandertal facial architecture in terms of peak bite force dissipation, but rather on large tooth size to better resist wear and abrasion from submaximal (but more frequent) biting and grinding forces. We conclude that masticatory biomechanical adaptation does not underlie variation in the facial skeleton of later Pleistocene Homo in general, and that continued exploration of alternative explanations for Neandertal facial architecture (e.g., climatic, respiratory, developmental, and/or stochastic mechanisms) seems warranted.

Tooth wear and dentoalveolar remodeling are key factors of morphological variation in the Dmanisi mandibles

“…4B and Fig. S3B), thus providing support for the hypothesis that mesiodistal forces and masticatory biomechanics were largely similar in these groups (48).…”

High‐Resolution Three‐Dimensional Computer Simulation of Hominid Cranial Mechanics

“…For the homogeneous model, all brick elements were assigned a single set of material properties for cortical bone (Young's modulus of Elasticity [Y] 5 27.0 GPa; Poisson's ratio 5 0.4; density 5 2,190 Kg/m Calculations of muscle forces were based on a dry skull method using estimates for cross-sectional area (Thomason, 1991;Wroe et al, 2005;Christiansen and Wroe, 2007) adjusted for application to hominids (O'Conner et al, 2005). In each simulation, the 3-D architecture and actions of the musculature were approximated using pretensioned trusses, beam finite elements that carry axial loads only (Fig.…”

“…Regions of particular interest with respect to feeding mechanics in the hominid skull include the zygomatic arches, supraorbital torus (brow-ridge) and orbital bar (Hylander et al, 1991;Hylander, 1997;O'Conner et al, 2005). These regions were selected within the models and analyzed statistically using a program written in RGui by K. Moreno.…”

Hominin lower second premolar morphology: evolutionary inferences through geometric morphometric analysis

“…Such compensation may indicate a biomechanically demanding diet, which might be supported by work on the anterior dentition that suggests Neandertals experienced heavy paramasticatory loads (Brace, 1963;Smith, 1983;Rak, 1986;Trinkaus, 1987;Demes and Creel, 1988) or intense, repetitive occlusal loads (O'Connor et al, 2003). In the case of the anterior dentition, selection favored a dental morphology better adapted to a biomechanically demanding diet (Molnar, 1971;Y'Edinak, 1978), and this could also apply to posterior dentition, despite its size reduction.…”