The faces of primates exhibit a variety of shapes, particularly around the bony orbits, which house the eyes. It is not known whether this variety reflects differences in adaptations to feeding or adaptations to vision. Recent research has suggested that the bones around the orbit are strained very little during feeding, and a suite of "nonfeeding" explanations for the evolution of the primate orbital region have been proposed. It has also been suggested that the orbital region might be adapted for resisting feeding forces in some primates, but not in others. The research proposed here will determine whether there are differences between monkeys, apes and humans on one hand, and bushbabies on the other in the functioning of the orbital region during feeding. In contrast with the diversity in primate facial shape, primates seem to move their jaws in similar ways. This suggests that primates might have evolved their shape differences within the limits dictated by an ancient, conserved, behavior pattern shared with other mammals. This research will collect data on simultaneous jaw movements and muscle activity in several species of primates to determine whether changes in bony form really have proceeded without significant changes in the way primates move their jaws and fire their chewing muscles.
