  Partner selection is an important process in many social interactions,
permitting individuals to decrease the risks associated with cooperation. In
large populations, defectors may escape punishment by roving from partner to
partner, but defectors in smaller populations risk social isolation. We
investigate these possibilities for an evolutionary prisoner's dilemma in which
agents use expected payoffs to choose and refuse partners. In comparison to
random or round-robin partner matching, we find that the average payoffs
attained with preferential partner selection tend to be more narrowly confined
to a few isolated payoff regions. Most ecologies evolve to essentially full
cooperative behavior, but when agents are intolerant of defections, or when the
costs of refusal and social isolation are small, we also see the emergence of
wallflower ecologies in which all agents are socially isolated. In between
these two extremes, we see the emergence of ecologies whose agents tend to
engage in a small number of defections followed by cooperation thereafter. The
latter ecologies exhibit a plethora of interesting social interaction patterns.
Keywords: Evolutionary Game; Iterated Prisoner's Dilemma; Partner Choice and
Refusal; Artificial Life; Genetic Algorithm; Finite Automata.
