A Darwinian legacy to understanding human infancy: emotional expressions as behavior regulators.

Darwin's influence on the study of emotional responding has largely centered on the study of the production of facial movement patterns. In this paper, we present evidence on the importance of considering facial and vocal patterns as signals that powerfully regulate behavior in infancy and early childhood. We review a series of studies showing that facial expressions and vocal expressions alone can regulate the behavior of infants and, in the case of vocal expressions, do so at ages earlier than most researchers have acknowledged. We also review studies on the enduring effects of social signals, documenting that even 8.5-month-olds show minimal retention of the effects of social signals, some 10-month-olds can retain the effects of social signals for 25 minutes, and 14-month-old can do so for a period of one hour after only two trials of signal exposure. Social signals not only regulate behavior, they also are part and parcel of an important and relatively unstudied phenomenon called affect sharing, which is evident by 11.5 months of age. Finally, we speculate on the constitutive role of social signals, especially those linked to what Ekman has called "basic emotions" in the generation of new emotions, such as pride, shame, and guilt.