Note: This workshop was jointly held with Center for Experimental Research in Social Sciences, Hokkaido University.

Date: August 24, 2010 (Tuesday) 10:00-12:00

Location: Hokkaido University, Faculty of Letters, room E204

Speakers: Yen-Sheng Chiang (Department of Sociology,University of California, Irvine)

Title: “Group homophily and the emergence of upstream reciprocity”

Participants: Nobuyuki Takahashi, Tatsuya Kameda, Toshio Yamagishi, Masaki Yuki, Taiki Takahashi, and Others (20 participants). Total 25 Participants.

Contents: 
The most pristine definition of reciprocity states that one returns what is received 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 further a chain of actions of reciprocity. 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 Roch (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 model that mixing group homophily with heterophily to a certain degree is beneficial to the propagation of cooperation in the evolutionary dynamics of upstream reciprocity.