The Emergence of "Us and Them" in 80 Lines of Code: Modeling Group Genesis in Homogeneous Populations

Kurt Gray*, David G. Rand, Eyal Ert, Kevin Lewis, Steve Hershman, Michael I. Norton

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

Psychological explanations of group genesis often require population heterogeneity in identity or other characteristics, whether deep (e.g., religion) or superficial (e.g., eye color). We used agent-based models to explore group genesis in homogeneous populations and found robust group formation with just two basic principles: reciprocity and transitivity. These emergent groups demonstrated in-group cooperation and out-group defection, even though agents lacked common identity. Group formation increased individual payoffs, and group number and size were robust to varying levels of reciprocity and transitivity. Increasing population size increased group size more than group number, and manipulating baseline trust in a population had predictable effects on group genesis. An interactive demonstration of the parameter space and source code for implementing the model are available online.

Original languageAmerican English
Pages (from-to)982-990
Number of pages9
JournalPsychological Science
Volume25
Issue number4
DOIs
StatePublished - Apr 2014

Keywords

  • intergroup dynamics
  • prejudice
  • social structure

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