Editing Evolutionarily stable strategy (section)

==Motivation==

The [[Nash equilibrium]] is the traditional [[solution concept]] in [[game theory]]. It depends on the cognitive abilities of the players. It is assumed that players are aware of the [[extensive form|structure of the game]] and consciously try to predict the [[Move (game theory)|moves]] of their opponents and to maximize their own [[Payoff (game theory)|payoffs]]. In addition, it is presumed that all the players know this (see [[common knowledge (logic)|common knowledge]]).  These assumptions are then used to explain why players choose Nash equilibrium strategies.

Evolutionarily stable strategies are motivated entirely differently.  Here, it is presumed that the players' strategies are biologically encoded and [[heritable]].  Individuals have no control over their strategy and need not be aware of the game.  They reproduce and are subject to the forces of [[natural selection]], with the payoffs of the game representing reproductive success (biological [[fitness (biology)|fitness]]). It is imagined that alternative strategies of the game occasionally occur, via a process like [[mutation]]. To be an ESS, a strategy must be resistant to these alternatives.

Given the radically different motivating assumptions, it may come as a surprise that ESSes and Nash equilibria often coincide. In fact, every ESS corresponds to a Nash equilibrium, but some Nash equilibria are not ESSes.