Introduced by John Maynard Smith and George R. Price in 1972/3,[1][2] it is an important concept in behavioural ecology, evolutionary psychology, mathematical game theory and economics, with applications in other fields such as anthropology, philosophy and political science.
Evolutionarily stable strategies were defined and introduced by John Maynard Smith and George R. Price in a 1973 Nature paper.
In fact, the ESS has become so central to game theory that often no citation is given, as the reader is assumed to be familiar with it.
Maynard Smith was jointly awarded the 1999 Crafoord Prize for his development of the concept of evolutionarily stable strategies and the application of game theory to the evolution of behaviour.
It is assumed that players are aware of the structure of the game and consciously try to predict the moves of their opponents and to maximize their own payoffs.
They reproduce and are subject to the forces of natural selection, with the payoffs of the game representing reproductive success (biological fitness).
It is imagined that alternative strategies of the game occasionally occur, via a process like mutation.
Given the radically different motivating assumptions, it may come as a surprise that ESSes and Nash equilibria often coincide.
A Nash equilibrium is presumed to be stable even if T scores equally, on the assumption that there is no long-term incentive for players to adopt T instead of S. This fact represents the point of departure of the ESS.
It also allows for a natural definition of related concepts such as a weak ESS or an evolutionarily stable set.
For example, in harm thy neighbor (whose payoff matrix is shown here) both (A, A) and (B, B) are Nash equilibria, since players cannot do better by switching away from either.
[11] B. Thomas (1984) applies the term ESS to an individual strategy which may be mixed, and evolutionarily stable population state to a population mixture of pure strategies which may be formally equivalent to the mixed ESS.
In finite populations, any mutant could in principle invade, albeit at low probability, implying that no ESS can exist.
One solution to this problem is to introduce the possibility of retaliation by having individuals play the game repeatedly against the same player.
Three simple contingency plans which have received substantial attention are Always Defect, Always Cooperate, and Tit for Tat.
This demonstrates the difficulties in applying the formal definition of an ESS to games with large strategy spaces, and has motivated some to consider alternatives.
The fields of sociobiology and evolutionary psychology attempt to explain animal and human behavior and social structures, largely in terms of evolutionarily stable strategies.
Sociopathy (chronic antisocial or criminal behavior) may be a result of a combination of two such strategies.
[15] Evolutionarily stable strategies were originally considered for biological evolution, but they can apply to other contexts.