The Masticatory Apparatus of Humans (Homo sapiens): Evolution and Comparative Functional Morphology

Abstract

Feeding and diet played key roles in human evolution. It is well known that modern humans have a small masticatory apparatus for their body size among primates. However, identifying gracility does not necessarily tell us about the relative functional capacities of the human masticatory system beyond the obvious size-related consequences. We consider the functional consequences of gracilization and functional relationships within the human masticatory apparatus using nonhuman primates for comparison. Human jaws are short for their size, particularly the anterior portion, among primates. When considered relative to masticatory apparatus size, the shortened jaw compares more similarly to other apes. Because jaw length acts as a load arm, humans have improved leverage for biting, but smaller relative gapes. Human biting ability is not particularly improved by their favorable leverage because humans have relatively small muscles and because of a size-related decrease in bite force across primates. Humans have relatively reduced load resistance abilities in the jaw compared to other apes, but abilities that are still intermediate among primates. Human postcanine teeth are small for their size, but average-sized for their masticatory apparatus. Finally, an initial look at jaw-muscle activation patterns during chewing suggests that humans recruit their jaw muscles like similar-sized anthropoids. We conclude that any performance deficits in the human masticatory apparatus are primarily related to gracilization. Humans possess a relative masticatory apparatus configuration that compares similarly to many other primates suggesting the evolution of humans has not unraveled the basic functional relationships within the masticatory apparatus that characterize most primates.