Birds of different feathers cooperate together: No evidence for altruism homophily in networks

Abstract

Many evolutionary models of cooperation assume that altruists possess telltale signs of disposition that they use to find and selectively associate with each other. Prior research finds that people can detect these signs of altruism in strangers, but we do not yet know whether this results in altruism homophily. We argue that dispositions should matter less in repeated interactions, where behavior is based on reciprocity. As a consequence, we should not expect people to have accurate insight into the dispositions (egoism vs. altruism) of their friends, nor should we expect these relations to be characterized by altruism homophily. Three studies, employing diverse methodologies and measures, find no evidence of altruism homophily. Moreover, we find that people have poor insight into their friends' altruism. We discuss the implications of these findings for the emergence of altruism and the role of embedded interactions in sustaining human cooperation.