Expression Of Emotion In Nonhuman Animals

Abstract

Abstract Darwin’s The Expression of Emotions in Man and Animals (1872/1998) was the first book to provide explicit links between how human and nonhuman animals express emotions, and it serves as a model for the study of emotional expression today. Darwin’s main focus was with the visual display of emotion. Although Darwin wrote briefly about vocalizations in nonhuman animals, it was much easier in his time to record and analyze facial expressions through drawings and the emerging new medium of photography. In the middle of the 20th century, the development of tape-recording equipment, coupled with technology originally developed for speech recognition, provided a means for accurate recording, description, and analysis of vocalizations. The last 50 years of experimental research on animal communication have been dominated by studies on vocal communication. With the recent advent of digital photography and editing systems, there has been an increased interest in the experimental study of visual signals. Darwin introduced his volume with three general principles of emotional expression that have formed the theoretical basis of current research. The first principle of “serviceable associated habits” provides that under certain mental (emotional) states various complex actions relieve or gratify sensations and desires, and that through repeated association, these actions might be found in circumstances where they might not be directly useful or they might be brought under voluntary control. Several suggestions follow from this principle. First, emotional expressions might be developed from normal physiological reactions to various internal or external stimuli. Thus the rapid expulsion of air and vocalization (“ooof”) that automatically results when we are hit in the stomach might become associated with other painful stimuli that do not result in a rapid expulsion of air. The resulting vocalization becomes an expression of pain experienced anywhere, and might even be used in anticipation of a painful stimulus to inhibit the infliction of pain by someone else. The conversion of an initial physiological reaction into a signal that represents an emotional state more directly is called ritualization by ethologists (Smith, 1977). Through progressive association, the physiological signal becomes more stereotyped in form, generalized to a broader array of contexts and universally used within a species. The fact that many signals are thought to have developed through ritualization of initial physiological reactions should not lead us to conclude that all apparent signals have been adapted for communication. Recently, Blumberg and Alberts (1997) have pointed out several examples of apparent signals that probably do not serve a communicative function to the producer of the signal.