Former SFI postdoctoral fellow Dan Hruschka's book, Friendship: Development, Ecology, and Evolution of a Relationship, explains why friends are more generous and cooperative with each other in ways that appear to defy evolutionary benefit.
In the book Hruschka synthesizes an array of cross-cultural, experimental, and ethnographic data to argue that friendship is a special form of reciprocal altruism based not on tit-for-tat accounting or forward-looking rationality, but rather on mutual goodwill that is built up along the way in human relationships.
Hruschka is an Assistant Professor in the Arizona State University's School of Human Evolution and Social Change. He completed the manuscript for the book, and much of the research, while at SFI as a postdoctoral fellow (2006-2009).
University of California Press book listing