Nash Equilibrium

Biological Parallel

In territorial fish, 50% of males adopt aggressive 'bourgeois' strategies while 50% adopt sneaky 'satellite' strategies. Neither strategy can invade the other—if too many fish go bourgeois, satellite pays off; if too many go satellite, bourgeois dominates. This stable mix is a Nash equilibrium, formalized as an Evolutionarily Stable Strategy (ESS). No individual can improve fitness by unilaterally changing strategies. Game theory and evolutionary biology converged on the same mathematics because both model systems where success depends on what others are doing.