Core-periphery segregation in evolving prisoner's dilemma networks

Dense cooperative networks are an essential element of social capital for prosperous societies. These networks enable individuals to overcome collective action dilemmas by enhancing trust. In many biological and social settings, network structures evolve endogenously as agents exit relationships and build newones. However, the interplay between game strategy and interaction structure by which evolutionary dynamics leads to self-organization of dense cooperative networks has not been understood. Our prisoner's dilemma experiments with exit and partner choice options show that core-periphery segregation of cooperators and defectors drives the emergence of cooperation. Cooperators' Quit-for-Tat and defectors' Roving strategy lead to a highly asymmetric core and periphery structure. Densely connected to each other at the core, cooperators successfully isolate defectors at the periphery and earn larger payoffs.