Leda Cosmides received her Ph.D. from Harvard University, and John Tooby also received his Ph.D. from Harvard University. She is Associate Professor of Psychology and he is Professor of Anthropology at the University of California Santa Barbara. They are co-directors of UCSB's Center for Evolutionary Psychology, where they have pioneered this emerging field in its goal of understanding universal cognitive and neural architecture as evolutionary responses to adaptative challenges. They have published widely on interactions between genetic, cognitive, and cultural dimensions of human social behavior, and together, along with Jerome Barkow, they edited the seminal The Adapted Mind: Evolutionary Psychology and the Generation of Culture.

Three long-standing theories for the evolution of altruism are kin selection, reciprocation, and group selection. We think that these are only three pathways out of a larger set, and that other pathways - what we call engagement models - have led to the evolution of a rich set of neuropsychological adaptations underlying friendship, romantic love, and certain moral sentiments. Our research into the cognitive and neural underpinnings of reciprocation have indicated how different the structure of friendship and love are from strict reciprocation, highlighting the need for alternative evolutionary explanations for these phenomena. Engagement models allow one to understand aspects of the design and social dynamics of human friendship, mateship, parenting, and kinship that are otherwise mysterious, such as why overt and explicit reciprocation is taken as a sign of the absence of friendship, and why human mating so often engenders deep feelings of commitment and sacrifice. While reciprocation depends on the economists’ model of exchange, the engagement models we develop depend on concepts of substitutability, interdependence, positive and negative externalities, association value, insurance, and niche limitation. We believe selection pressures relating to these variables have constructed specialized motivational, emotional, and inferential circuitry that supply an additional dynamics to human altruism that is nearly absent from other species.