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Glossary · Game Theory

Evolutionarily Stable Strategy

also: ESS · evolutionary game theory · replicator dynamics · hawk-dove game · frequency-dependent selection

Definition

An evolutionarily stable strategy is one that, once adopted by a population, cannot be invaded by any rare alternative. Maynard Smith and Price (1973) introduced it to explain restraint in animal conflict; applied to markets it explains why competitors converge on identical positioning and why a deviant strategy pays only if it reaches critical mass before it is copied.

Evolutionary game theory drops the assumption that players reason. Strategies spread according to replicator dynamics: whatever earns above-average payoff grows its share of the population. The hawk-dove game is the workhorse: when the cost of fighting exceeds the value of the prize, the stable state is a mixture of aggressive and conciliatory play, not the victory of either. Marketing categories behave the same way. Once most firms run the same playbook, the payoff to any one firm of deviating depends on how many others deviate, which is frequency-dependent selection. Hotelling (1929) supplies the spatial version, minimum differentiation, and d'Aspremont, Gabszewicz, and Thisse (1979) the correction under which firms separate. The framework predicts convergence, cycles, and the narrow windows in which a mutant strategy can take over.

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