Evolution of conditional cooperation in a spatial public goods game

Spatial structure is one of the mechanisms that allows the evolution of cooperation, especially in dyadic interactions. However, when interactions occur within groups, the effectiveness of spatial structure is reduced, and additional mechanisms to sustain cooperation are needed. Conditional cooperation strategies are commonly adopted in strategic interaction, but not extensively investigated in the context of spatial reciprocity, despite potentially changing the dynamic of the evolution of cooperation. We propose and model a public good game where agents spatially interact in groups and adopt conditional cooperation strategies. We show that cooperation is evolving with no need for additional mechanisms apart from spatial structure when agents follow conditional strategies. We confirm the positive influence of productivity and cluster formation on the evolution of cooperation in spatial models. Our results are robust for two types of conditional cooperation strategies.Author Summary: We study the evolution of cooperation using a computational model that allows us to simulate evolutionary dynamics and shows the conditions under which cooperation observed in collectives could emerge. Cooperation is a widespread behavior in biological and human systems that allows groups to function and thrive, but it constitutes a puzzle for evolutionary theories: how is it that individuals sacrifice resources to benefit the interest of the group? Can evolution favor this behavior? Previous studies have shown that constraining individuals to local interactions favors the emergence of cooperation, making altruistic behavior possible. However, when interactions are scaled to bigger groups, this spatial constraint alone is not sufficient for cooperation to evolve. We show that by just allowing the use of conditional strategies (“I cooperate if enough others cooperate”), which are commonly adopted by humans in real life, cooperation is sustained with no need for additional mechanisms other than spatial interaction. Our results show the effectiveness of conditional cooperation behavior and how simple behavioral rules help overcome some of the challenges posed by group interactions. These findings contribute to explaining the extended cooperation we find in nature and human societies.