Norm heterogeneity and the emergence of cooperation A spatial agent-based model of conditional cooperation

The resolution of collective-action problems often depends on social norms and pressure to conform to group behaviour, yet individuals typically differ in how strongly they perceive and internalise these norms. While existing models of norm change and social tipping often assume homogeneous and static normative expectations, recent evidence suggests substantial heterogeneity in the perceived norm strength. We study how different compositions of such heterogeneity within a community shape the emergence and internalisation of cooperative behaviour. We develop a spatial agent-based model in which agents follow a conditional-cooperation norm but differ in norm strength, characterised as either tight or loose. Agents interact locally and update their cooperation thresholds endogenously through a combination of payoff-driven learning and social learning from experiencing group behaviour. Our results show that introducing a moderate share of loose-norm individuals into otherwise tight-dominated communities can facilitate the emergence of cooperative tipping points by enabling cooperation to seed and spread locally, even when agents place zero weight on social-relative-to-financial learning. However, whether cooperation becomes internalised and persists depends critically on the relative weight given to social and financial learning. A higher weight on social learning amplifies local behavioural feedbacks, sharpens tipping-point dynamics, and allows agents with tight social norms to internalise cooperation such that it can be sustained with fewer cooperating group members. Once cooperation spreads, conformity pressure stabilises cooperative behaviour among loose-social-norm agents. Taken together, our findings highlight the importance of community composition and norm-strength heterogeneity for collective-action dynamics, and show how heterogeneity in perceived norm strength can generate abrupt and persistent transitions in cooperative behaviour.