How and why emotions are expressed

Abstract Empirical research on emotion is flourishing. Much of this research has focused on emotional expressions—dynamic patterns of behaviours including facial movements, vocalizations, bodily movements, gaze patterns, gestures and autonomic responses like blushing. However, research to date has primarily focused on perceptions of others' emotional expressions rather than on the production of emotional expressions. This theme issue shifts the focus to the intra-personal level, centring processes in the expresser. Using Tinbergen's ethological framework, this theme issue examines four levels of analysis: mechanisms, development, phylogeny and function. The contributions demonstrate that the production of emotional expression involves distributed, multi-level mechanisms, including appraisal, central emotion circuits and interoceptive signalling, that reciprocally interact to generate emotional expressions. Developmentally, emotional expression production depends both on maturation and learning through social experience. Comparative work illustrates how behavioural indicators allow inferences about emotional states across taxa, revealing both shared and divergent properties of emotions that relate to ecology, social structure and cognitive capacities. Finally, the issue highlights intraindividual functions of emotional expressions alongside their social functions, shedding new light on why emotional expressions have evolved. Here, we synthesize the contributions and set out a new research agenda on how and why emotions are expressed. This article is part of the theme issue ‘Mechanisms, development, phylogeny and functions of emotional expressions’.