 The Smith Dynamics. One unusual feature of the learning rule which generates the BNN dynamic is that it compares the expected payoff of alternative possible strategies with the average payoff of the population. One might wonder why performing better than the population average is a sensible point of comparison, since the average payoff of the population is often not actually achievable by any particular strategy available to the players. Instead, consider the learning rule which compares the expected payoff of one’s current strategy, in the present population state, with the expected payoff of other possible strategies, in the present population state, but where only those alternative strategies which have a higher expected payoff have a nonzero probability of being adopted. When plugged into the Sandholm framework above, this learning rule generates an evolutionary dynamic first studied by Smith (1984) and is thus known as the Smith dynamic.