The Faces Monkeys Make

In the 140-plus years since Darwin popularized the study of nonhuman animal emotion, interest in the emotional lives of nonhuman animals has expanded rapidly. On the basis of Darwin’s anecdotal observations about facial behaviors, it is often assumed that facial behaviors give evidence of emotion in both humans and nonhuman animals. These assumptions are then used to support claims about the evolution of emotion. In this chapter, we explore the empirical evidence about the structure and meaning of facial behaviors generated by macaque monkeys. Evidence indicates that individual facial behaviors occur in a wide variety of contexts and subserve a variety of social functions. Furthermore, macaques are not particularly good at discriminating between all facial behavior categories. Taken together, the evidence suggests that facial behaviors in macaques do not give evidence of specific emotions, but rather serve as complex social signals.