  Despite the popularity of replicator dynamics, critics such as H. Peyton Young (1998) remain skeptical. The most natural motivation for replicator dynamics is biological. We conceptualize players as animals genetically programmed to exhibit certain behaviors. Creatures who achieve higher payoffs have higher reproductive fitness, and they pass their strategy choices along to their progeny. Natural selection therefore causes certain behaviors to become more prevalent. Under these assumptions, replicator dynamics seems plausible. But it is not clear that a comparable rationale applies to human interaction, since humans generally act not based solely upon their genetic programming but rather upon their beliefs and desires. Why should the choices of individual human agents yield the pattern described by replicator dynamics?