The biological origins of automated patterns of human interaction are explored. Automated patterns of interaction are distinguished from deliberate patterns. Automated patterns consist of two particular types: stimulation regulation and emotional responsiveness. Evidence for the biological origins of these patterns is obtained by studying the early interactions of infants and neonates, surveying the ethological parallels, exploring the evolutionary adaptiveness of the specific patterns, and ascertaining physiological, psychopharmacological, and brain mechanisms responsible for the patterns. Although circumstantial, the case for a biological basis for stimulation regulation and emotional responsiveness is very suggestive.