Iterated Prisoner's Dilemma with Choice and Refusal of Partners

This paper studies the effects of partner selection on cooperation in an artificial ecol ogy. Agents, represented by finite automata, interact with each other through an iterated prisoner's dilemma (IPD) game with the added feature th-at players choose and refuse potential game partners on the basis of continually updated expected payoffs. Analytical studies reveal that the subtle interplay between choice and refusal in iV-player IPD games can result in various long-run player interaction patterns: e.g., mutual cooperation; mixed mutual cooperation and mutual defection; parasitism; and/or wallflower seclusion. Simu lation studies indicate that choice and refusal can accelerate the emergence of cooperation in evolutionary IPD games. -More generally, however, choice"and refusal can result in the emergence and persistence-of multiple payoff bands, reflecting the possible existence of ecological attractors characterized by play behavior that is not entirely cooperative. The existence of a spectrum of payoff bands in turn leads to the emergence of new ecological behaviors such as band spiking and band tuimeling.