A biomechanical perspective on understanding facial variation and dietary transitions: Trabecular architecture of the Pleistocene and Holocene human mandible

PhD Candidate: KS Duffett Carlson
Supervisor: Professor Ron Pinhasi
Funded By:Irish Research Council

Abstract

Understanding the diet of an organism is fundamental to determining its behavioural repertoire, ecological role, and evolutionary trajectory. This is achievable through direct observation in living taxa, but the dietary constraints, and adaptations of extinct taxa must be assessed through comparative anatomical and biomechanical analyses. Such analyses demonstrate that consumption of softer foods since the adoption of agriculture, and the reduced mechanical loads they place on the jaws, have produced a comparatively gracile mandible, dental crowding, and increased caries in anatomically modern Homo sapiens (AMH). Although the relatively robust Neanderthal mandible exhibits pronounced anterior dental attrition and large molars that suggest adaptation to extensive occlusal loading, these traits are frequently dismissed as non-adaptive or retained. This assessment conflicts with our understanding of rapid morphological change in AMH during the agricultural transition. The pertinence of orofacial morphological to taxonomic designation and correlation to masticatory loading, suggests that this position merits revaluation.

The internal lattice of bones, called trabeculae, are shown to remodel in vivo in response to mechanical loading. Variation in their architecture is demonstrated to reflect behavioural differences in the postcrania of archaeological populations, and in the jaws of modern humans as assessed through clinical dentistry. Thus, the internal architecture of the mandible should reflect variation in masticatory loading of an individual's diet in relation to morphological and biomechanical variability. My research therefore explores how trabecular architecture varies within and between human populations by examining volumes of interest extracted from biomechanically relevant portions of the mandible using high-resolution micro-computed tomography scans of AMH and Neanderthal populations. It specifically assesses the following: 1) whether geographically and temporally distinct groups differ in their trabecular microarchitecture, and; 2) whether structural variables correspond to loads incurred during dietary and paramasticatory behaviours.