 Although extortionary ZD strategies fare poorly under evolution, Hilbe et al., suggest that they do play an important evolutionary role, as “catalysts” for the evolution of cooperation. They explore in some detail the course of evolution among agents restricted to a small choice of strategies, including unconditional defection, an extortionary ZD strategy and the familiar (relatively cooperative) strategy \(\bP_1\). In the absence of extorters, unconditional defection predominates in a population of any size. In the presence of extorters, however, \(\bP_1\) becomes more successful as population size increases. In populations larger than fifty, it predominates. The same basic results hold when unconditional cooperation is added as a strategy choice. In the absence of extortionary strategies TFT can play a similar catalytic role, allowing \(\bP_1\) to predominate over unconditional defection (with or without unconditional cooperators present). The short explanation is that TFT and the extortionary strategies can both drift into a population of unconditional defectors as neutral mutants, and the proportion of TFT can grow for a time. Eventually, however, \(\bP_1\) will do better than either.