The Development of Hominin Muscles of Mastication

Abstract

The temporalis muscle travels through the zygomatic arch, attaching the mandible to the cranium, and facilitating mandible elevation. This elevation is what constitutes the motion of chewing, or mastication. Hominins are primates belonging the same evolutionary line as modern humans, including species like Australopithecus afarensis, Homo neanderthalensis, and Ardipithecus ramidus. Stress upon the mastication musculature from the act of chewing can cause direct impacts on the bones of the skull, widening the space of the zygomatic arch or cheek bone, and forming a sagittal crest on top of the head. These stressors are often caused by diet and what the density or type of food the subject is consuming as well as the numbers of hours spent chewing per day. This project examines the size of the zygomatic arch, postorbital constriction, palate breadth, and molar size in order to gain a better understanding of the evolutionary development of modern human mastication and the diets of our ancestors. The general trend is a reduction in the robusticity of the masticatory system over time, coinciding with the adoption of cooking, greater incorporation of meat in the diet, and subsequent increase in brain size.