Comment: Final preprint of a manuscript accepted for publication in the Journal of Economic TheoryWe study population dynamics under which each revising agent tests each strategy k times, with each trial being against a newly drawn opponent, and chooses the strategy whose mean payoff was highest. When k = 1, defection is globally stable in the prisoner`s dilemma. By contrast, when k >
1 we show that there exists a globally stable state in which agents cooperate with probability between 28% and 50%. Next, we characterize stability of strict equilibria in general games. Our results demonstrate that the empirically plausible case of k >
1 can yield qualitatively different predictions than the case of k = 1 that is commonly studied in the literature.