A survey of the literature reveals that many who have commented on the signaling of animals ascribe to the view that all of their communicative signals are manifestations of emotion or affect. If this view were correct, then animal signals would have much in common with certain human facial expressions, widely regarded by some, if not by all, as uniquely revealing signs of emotion. The prevalence of this interpretation of animal signals is evident in the comments displayed in Table 6.1 on the vocalizations of monkeys and apes, drawn from a wide range of disciplines. Either explicitly or implicitly, each of them assumes parallels with human expressions of emotion. One aim of a program of research extending over a period of 15 years has been to subject the interpretation of animal signals as emotion-based to a critical appraisal. This chapter reviews some of the evidence that has been forthcoming and the possibility that it bears on our understanding of human emotional expressions.

As a point of departure, we began our studies by consulting dictionary definitions of emotion, of which we take the following, from the Random House Dictionary of the English Language (1981, p. 467), to be representative. “Emotion: an affective state of consciousness in which joy, sorrow, fear, hate, or the like, is expressed, as distinguished from cognitive and volitional states of consciousness” – “usually accompanied by certain physiological changes, as increased heartbeat, respiration or the like, and often overt manifestation, as crying, shaking, etc.”