T h e biological origins of automated patterns of-human interaction are explored. Automated patterns of interaction are distinguished f r o m 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 f o r the putterns. Although circumstantial, the case f o r a biological basis for stimulation regulation and emotional responsiveness is w r y suggestive.Consider what one can mean by the origins of a set of human behaviors. Origins can be located in learning, through the social, cultural, and environmental forces impinging on the organism. They can be located in the set of causal forces that produce the immediate behaviors under scrutiny. Origins can also be found in the set of logical operators that give rise to the set of all possible behaviors within a given domain, as Chomsky's (1957) grammatical operators did for language. Finally, the origins of a set of behaviors can be located in the biological, genetic, and evolutionary forces that are ultimately responsible for the behavior set. These four domains may be labeled nurture, proximate causality, logical generation, and nature.A student of human behavior interested in understanding behavior in its fullest would be unwise to neglect any of these aspects of a behavior's origins. To do so would be like trying to understand the volume of a complex geometric figure (like a duodecahedron) by measuring its height. It just will not work. That caveat offered, the focus of this article will nevertheless be limited to the biological origins of human interaction, locating itself on nature's side of the nature-nurture debate.Why should one focus o n the biological origins of human interaction? Forgetting about the "human interaction" component for the moment, several factors recommend a consideration of the ultimate origins of a behavior pattern. First, in the field of communication studies, the preeminent forms of explanation of human behavior have been the social and psychological. The reasons for this are as much accidents of history, linked to the roots of communication studies in social psychology, as they are a result of rational consideration of the set of explanatory forces operative in human conduct. Recent trends indicate an even larger role in 4