Evolutionary game theory

Ever since Darwin read Malthus, the theory of evolution has benefited from the interaction of ecology with economics. Evolutionary game theory belongs to this tradition: it merges population ecology with game theory. Game theory originally addressed problems confronted by decision makers with diverging interests (for instance, firms competing for a market). The ‘players’ have to choose between strategies whose payoff depends on their rivals’ strategies. This interdependence leads to a mutual ‘outguessing’, as with chess (she thinks that I think that she thinks...). There usually is no solution that is unconditionally optimal, no matter what the co-players are doing. In the context of evolutionary biology, the two basic notions of game theory, namely strategy and payoff, have to be re-interpreted. A strategy is not a deliberate course of action, but an inheritable trait; payoff is Darwinian fitness (average reproductive success). The ‘players’ are members of a population, all competing for a larger share of descendants. If several variants of a trait occur in a population, then natural selection leads to an increase in the frequency of those variants with higher fitness. If the success of a trait does not depend on its frequency, this will eventually lead to the fixation of the optimal variant. But if the success of a trait is frequency-dependent, then its increase may lead to a composition of the population where other variants do better; this can be analysed by means of game theory. This is similar to what happens in population ecology. If prey is abundant, predators will increase for a while. But this increase reduces the abundance of prey, and eventually leads to a decrease of the predators.