Abstract
In a local interaction model agents play bilateral prisoners’ dilemmas with their immediate neighbors and have three possible strategies: altruistic, egoistic, and partial cooperation. After each period the agents adopt the strategy with the highest average payoff in their observed local neighborhood. There does not exist an absorbing state in which the partially cooperative strategy coexists with any of the other strategies. The partially cooperative strategy limits the diffusion of altruistic behavior in the population. Although clustering of altruists is beneficial for sustaining altruism, relatively big groups of altruists at the onset enable the spread of the partially cooperative strategy.