 We can represent the strategies for the evolutionary optional PD that do not require memory of previous interaction as triples \(\langle p,q,r \rangle\), where \(p\), \(q\) and \(r\) are real numbers adding to one, representing the probability of playing \(\bC\), \(\bD\) and \(\bN\). None of these strategies meets the BS condition, and so no strategy is rwb-stable within this family. If all the members of a group unconditionally refuse to engage (adopting \(\langle 0,0,1 \rangle\)), then they can be infiltrated and eventually replaced by small invasions of more cooperative strategies. The cooperative strategies, in turn, will be overthrown by defecting strategies, and, when the concentration of defectors is sufficiently great, the “loners” who refuse to engage can again take over. Adding the option of not-playing to the evolutionary PD does permit escape from from the unhappy state of universal defection, but leads to an only slightly less undesirable outcome in which a population cycles repeatedly through states of universal non-engagement. (Szabó and Hauert contains a nice picture of the phenomenon.)