Originally developed by applying models from cognitive psychology to the study of foreign policy decision making, the field of behavioral IR is undergoing important transformations. Building on a broader range of models, methods, and data from the fields of neuroscience, biology, and genetics, behavioral IR has moved beyond the staid debate between rational choice and psychology and instead investigates the plethora of mechanisms selected by evolution for solving adaptive problems. This opens new opportunities for collaboration between scholars informed by rational choice and behavioral insights. Examining the interactions between the individual's genetic inheritance, social environment, and downstream behavior of individuals and groups, the emerging field of behavioral epigenetics offers novel insights into the methodological problem of aggregation that has confounded efforts to apply behavioral findings to IR. In the first instance empirical, behavioral IR raises numerous normative and philosophical questions best answered in dialogue with political and legal theorists.