Diverse Behavior Patterns in a Symmetric Society with Voluntary Partnerships

We show that it is evolutionarily stable that some players behave cooperatively while others act myopically, after any length of "trust-building" phase, where the partners do not cooperate but keep the partnership, in the Voluntarily Separable Repeated Prisoner's Dilemma (Fujiwara-Greve and Okuno-Fujiwara, 2009). Each player is playing a pure strategy in a large homogeneous population. Hence diverse behavior patterns are stable. The logic is that "diverse mutants support diversity": when mutant strategies are spread over a large variety, the mutants exploit each other and the incumbent distribution is robust. Since there are infinite strategies, such uncoordinated mutation is plausible