Group Homophily and the Emergence of Upstream Reciprocity

Abstract

The most pristine definition of reciprocity states that one returns what’s/he receives to the giver. Upstream reciprocity, extending this definition, portrays a social system where the recipient of a favor directs his reciprocity to a different person rather than the original giver, thus pushing forward a chain of acts of reciprocity further. Examples of upstream reciprocity are ubiquitous in everyday life, but how it evolves to be part of human sociality has not been fully understood. Drawing on earlier work by Nowak and Rach (2007), we develop an evolutionary model to investigate how network structure influences the emergence of behaviors related to upstream reciprocity. Manipulating the degree to which network ties are linked within or across groups, we map out the relationship between the distribution of intra- and inter-group ties and the sort of behavior that emerges. We discover some intriguing insights from the simulation that mixing group homophily and heterophily is beneficial to the propagation of cooperation in the evolutionary dynamics of upstream reciprocity.