Evolution and facial action in reflex, social motive, and paralanguage.

Based upon current evolutionary theory and recent laboratory and field data, this paper introduces a behavioral-ecology view of human facial displays that contrasts with previous views of faces as innate, prototypic, "iconic" expressions of fundamental emotions. First, I detail the criteria for establishing genetic and epigenetic contributions to facial behavior. Under these criteria, cross-cultural communality in canonical facial displays implies neither their genetic control nor their fundamental relation to emotion. New findings reestablish phylogenetic continuity by showing that human facial displays and vigilance for them, like their nonhuman counterparts, coevolve in the service of social motives; faces issued in solitude typically reflect imaginary or implicit interaction. Two evolutionary trends are probably involved in shaping facial actions--emancipation of reflexes, and automatization of instrumental acts. Modern conceptions of genetic and cultural evolution, and knowledge about animal signaling, suggest new hypotheses regarding the origins and functions of facial displays. In so doing, they clarify how facial displays relate to reflexion, motive and intention, emotion and psychophysiology, and language and paralanguage.