 Linster simulated a variety of EPD tournaments among the two-state strategies. Some used “uniform mutation” in which each strategy in the population has an equal probability \(m\) of mutating into any of the other strategies. Some used “stylized mutation” in which the only mutations permitted are those that can be understood as the result of a single “broken link” in the Moore machine diagrams. In some, mutations were assumed to occur to a tiny proportion of the population at each generation; in others the “mutants” represented an invading force amounting to one percent of the original population. In some, a penalty was levied for increased complexity in the form of reduced payoffs for machines requiring more states or more links. As one might expect, results vary somewhat depending on conditions. There are some striking differences, however, between all of Linster's results and those of Nowak and Sigmund. In Linster's tournaments, no single strategy ever dominated the surviving populations in the way that \(\bP_1\) and GTFT did in Nowak and Sigmund's. The one strategy that did generally come to comprise over fifty percent of the population was the initially-cooperating version of \(\bS(1,0,0,0)\). This is a strategy whose imperfect variants seem to have been remarkably uncompetitive for Nowak and Sigmund. It has been frequently discussed in the game theory literature under the label GRIM or TRIGGER. It cooperates until its opponent has defected once, and then defects for the rest of the game. According to Skyrms (1998) and Vanderschraaf, both Hobbes and Hume identified it as the strategy that underlies our cooperative behavior in important PD-like situations. The explanation for the discrepancy between GRIM's strong performance for Linster and its poor performance for Nowak and Sigmund probably has to do with its sharp deterioration in the presence of error. In a match between two imperfect GRIMs, an “erronious” defection by either leads to a long string of mutual defections. Thus, in the long run imperfect GRIM does poorly against itself. The other strategies that survived (in lesser numbers) Linster's tournaments are TFT, \(\bP_1\), \(\bCu\), and the initially-cooperative \(\bS(1,0,1,1)\). (Note that imperfect GRIM is also likely to do poorly against imperfect versions of these.) The observation that evolution might lead to a stable mix of strategies (perhaps each serving to protect others against particular types of invaders) rather than a single dominant strategy is suggestive. Equally suggestive is the result obtained under a few special conditions in which evolution leads to a recurring cycle of population mixes.