Spatial Evolution of Automata in the Prisoners' Dilemma

This paper applies the idea of evolution to a spatial model. We assume that prisoners' dilemmas or coordination games are played repeatedly within neighborhoods where players do not optimize but instead copy successful strategies. Discriminatory behavior of players is introduced representing strategies as small automata, identical for a player but possibly in different states against different neighbors. Extensive simulations show that cooperation persists even in a stochastic environment, that players do not always coordinate on risk dominant equilibria in 2 x 2 coordination games and that success among surviving strategies may differ. We also present two analytical models that explain some of these phenomena.