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	Evolutionary Game Theory (Stanford Encyclopedia of Philosophy)
		In order for a strategy to be evolutionarily stable, it must have the property that if almost every member of the population follows it, no mutant (that is, an individual who adopts a novel strategy) can successfully invade.
		Roughly, if only two pure strategies exist, then given a (possibly mixed) evolutionarily stable strategy, the corresponding state of the population is a stable state under the replicator dynamics.
		This representation of strategy selection clearly presupposes hyperrational players and fails to represent the process by which one player observes his opponent's behavior, learns from these observations, and makes the best move in response to what he has learned (as one might expect, for there is no need to model learning in hyperrational individuals).
	plato.stanford.edu /entries/game-evolutionary (7258 words)

	NationMaster - Encyclopedia: Evolutionarily stable strategy
		The difference between a Nash equilibrium and an ESS is that a Nash equilibrium may sometimes exist due to the assumption that rational foresight prevents players from playing an alternative strategy with no short term cost, but which will eventually be beaten by a third strategy.
		An evolutionarily stable state is a dynamical property of a population to return to using a strategy, or mix of strategies, if it is perturbed from that strategy, or mix of strategies.
		ESS · Risk dominance In game theory, the Nash equilibrium (named after John Forbes Nash, who proposed it) is a kind of solution concept of a game involving two or more players, where no player has anything to gain by changing only his or her own strategy unilaterally.
	www.nationmaster.com /encyclopedia/Evolutionarily-stable-strategy (4740 words)

	Evolutionarily stable strategy - Wikipedia, the free encyclopedia
		The difference between a Nash equilibrium and an ESS is that a Nash equilibrium may sometimes exist due to the assumption that rational foresight prevents players from playing an alternative strategy with no short term cost, but which will eventually be beaten by a third strategy.
		An ESS is a strategy with the property that, once virtually all members of the population use it, then no 'rational' alternative exists.
		An evolutionarily stable state is a dynamical property of a population to return to using a strategy, or mix of strategies, if it is perturbed from that strategy, or mix of strategies.
	en.wikipedia.org /wiki/Evolutionarily_stable_strategy (1449 words)

	stable - Search Results - MSN Encarta (Site not responding. Last check: 2007-09-17)
		Stability, in physics and engineering, the property of a body that causes it to return to its original position or motion as a result of the action...
		Augean Stables, in Greek mythology, the stables owned by Augeas, a son of the god Helios and king of Elis in the north-western Peloponnese...
		Evolutionarily Stable Strategy (ESS), animal behaviour pattern, which when common in a population, cannot be out-competed (or, in evolutionary...
	uk.encarta.msn.com /stable.html (224 words)

	Evolutionarily stable strategy: Definition and Links by Encyclopedian.com
		The idea of an evolutionarily stable strategy (or ESS) was introduced by John Maynard Smith (with impetus from George Price) in an essay on "Game Theory and the Evolution of Fighting".
		An ESS depends on the idea of invasion, where a population of strategy-X players is visited by a strategy-Y player.
		A strategy X is evolutionarily stable if there is no strategy Y that can invade it.
	www.encyclopedian.com /ev/Evolutionarily-stable-strategy.html (391 words)

	Science Fair Projects - Evolutionarily stable strategy
		The evolutionarily stable strategy (or ESS; also evolutionary stable strategy) is a central concept in game theory introduced by John Maynard Smith and George R. Price in 1973 (a full account is given by Maynard Smith, 1982).
		It is based on a concept of a population of organisms playing a certain strategy, that a mutant allele that causes organisms to adopt a different strategy cannot invade the population, but will instead be selected out by natural selection.
		Both strategies A and B are ESS, since a B player cannot invade a population of A players nor can a A player invade a population of B players.
	www.all-science-fair-projects.com /science_fair_projects_encyclopedia/Evolutionarily_stable_strategy (900 words)

	Supplements to Procedural Analysis: PA and the ESS
		One overdue matter however is the treatment of PA in respect of John Maynard Smith's concept of the ESS (evolutionarily stable strategy).
		Stability in PA is the basic evolutionary viability of a single behaviour expressed by a single individual.
		The strategy confers numerous advantages to the female (detailed elsewhere) and hence increases her fitness (often, as here, defined as the number of grandchildren which ensue).
	www.heretical.com /sexsci/supp-ess.html (1110 words)

	Evolutionarily stable strategies Article, Evolutionarilystablestrategies Information (Site not responding. Last check: 2007-09-17)
		The evolutionarily stable strategy (or ESS; also evolutionary stable strategy) is a central concept in game theory introduced by John Maynard Smith and George R. Price in1973 (a full account is given by Maynard Smith, 1982).
		Assuming playersare able to choose and switch strategies, this would induce the indigenous population to start switching to strategy Y. In manycases there are diminishing returns for the later adopters, and what follows is an equilibrium ratio of strategy-X players tostrategy-Y players.
		(See theclosely-related Nash equilibrium.) ESS is stable in respect torandomly and occasionally occurring invading strategies, thus it is not stable in respect to mass counts of invaders.
	www.anoca.org /strategy/population/evolutionarily_stable_strategies.html (393 words)

	Psychology History
		He determined that the strategy behind a particular population is to resist the formation of new traits or characteristics, such as the length of a horn or whether to fight or retreat when faced with an opponent, since it may lessen the possibilities for successful reproduction.
		Evolutionarily stable strategy can be applied to the tit-for-tat strategy because it cannot be replaced by other strategies.
		His extensive research and work on game theory, evolutionarily stable strategy, and hawk and dove strategies has provided a greater understanding of animal behavior in relation to their reaction to predators and competition.
	www.muskingum.edu /~psychology/psycweb/history/smith.htm (1453 words)

	Bio 352 Lecture 9
		In a symmetric game the ESS is the strategy that is the best either opponent can do given the options (thus it cannot be "invaded" by an alternative....
		In an asymmetric game, the ESS will be a combination of a strategy by player 1 and another by player 2 that cannot be invaded by other combinations.
		There are four possible ways this ESS may be achieved depending on the relative payoffs of playing one strategy vs. the other for both of the opponent's possible plays
	www.lclark.edu /~clifton/behav/outlines/bio352lect9a.htm (724 words)

	SparkNotes: Behavioral Ecology: Game Theory
		This situation is a pure evolutionarily stable strategy (ESS).
		If both players choose strategy A, player 1 gets the better payoff of Q. If they both choose strategy B, player 1 receives the better payoff of T. Evolution will result in the frequency of played strategies moving toward what the majority of the population was already doing.
		The two strategies in a game can be played by different individuals who always play the same strategy (a polymorphic population), or both strategies may be played by any individual in a population (polymorphic individuals).
	www.sparknotes.com /biology/animalbehavior/behavioralecology/section2.rhtml (1249 words)

	Agorics, Inc. - Evolutionarily Stable Strategies
		Con men are not an ESS except in a trivial sense-a population consisting purely of con men cannot be invaded by a small, scattered group of TIT FOR TAT players.
		A population dominated by any strategy that is both nice and sufficiently retaliatory cannot be invaded by any strategy that is not.
		Therefore, the ESS of the Axelrod tournament is to be nice and retaliatory.
	www.agorics.com /Library/agoricpapers/ce/ce3.html (686 words)

	Introduction to Game Theory -- simple, two-strategy examples
		Strategies: The particular behavior or suite of behaviors that a player uses is termed a strategy (see important note).
		Strategies can be behaviors that are on some continuum (e.g., how long to wait or display) or they may represent discrete behavior types (e.g., display, fight, or flee).
		The pure ESS strategy will totally dominate the population except for occasional migrants, mutants, or individuals temporarily trying to gain any fitness they can (you can read more about persistence of low fitness individuals at the end of the section).
	www.holycross.edu /departments/biology/kprestwi/behavior/ESS/games_intro.html (7040 words)

	EconPapers: Evolutionary Stability in Asymmetric Population Games (Site not responding. Last check: 2007-09-17)
		Stability with respect to simultaneous entry of a small proportion of mutants into both populations is considered.
		Sets of neutrally stable strategy pairs such that for any pair of mutants not in the set at least one mutant is driven out are called evolutionary stable.
		Evolutionarily stable sets are shown to be equivalent to strict equilibrium sets.
	econpapers.repec.org /paper/bonbonsfb/314.htm (278 words)

	Evolutionarily stable strategy Summary
		In this particular population, the stable strategy is a mixture of doves and hawks.
		This could mean that individuals never change their strategies and that a combination of both strategies is stable, or that individuals may employ either strategy and switch strategies as often as they please.
		A preexisting ESS has probably been challenged by any number of alternate strategies and has survived, but it might be expected that only a completely new and innovative strategy would have a fighting chance at defeating it.
	www.bookrags.com /Evolutionarily_stable_strategy (2393 words)

	Evolutionary Game Theory (Stanford Encyclopedia of Philosophy/Winter 2003 Edition)
		In order for a strategy to be evolutionarily stable, it must have the property that if almost every member of the population follows it, no mutant (that is, an individual who adopts a novel strategy) can successfully invade.
		Roughly, if only two pure strategies exist, then given a (possibly mixed) evolutionarily stable strategy, the corresponding state of the population is a stable state under the replicator dynamics.
		This representation of strategy selection clearly presupposes hyperrational players and fails to represent the process by which one player observes his opponent's behavior, learns from these observations, and makes the best move in response to what he has learned (as one might expect, for there is no need to model learning in hyperrational individuals).
	www.science.uva.nl /~seop/archives/win2003/entries/game-evolutionary (7283 words)

	Evolutionarily stable strategy at AllExperts
		An ESS is defined to exclude such equilibria, and assumes only that natural selection prevent players from using strategies which lead to lower payoffs.
		The definition of an ESS was introduced by John Maynard Smith and George R. Price in 1973 (a full account is given by Maynard Smith's 1982 book Evolution and the Theory of Games) based on W.D. Hamilton's (1967) concept of an unbeatable strategy in sex ratios.
		If a player choosing strategy J in a population where all other players play strategy I receives a payoff of E(J,I), then strategy I is a Nash equilibrium if,:E(I,I) â¥ E(J,I)This equilibrium definition allows for the possibility that strategy J is a neutral alternative to I (it scores equally, but not better).
	en.allexperts.com /e/e/ev/evolutionarily_stable_strategy.htm (1369 words)

	BioMed Central \| Full text \| Analysis of disruptive selection in subdivided populations
		Some works made no distinction between the concepts of convergence and of evolutionary stability [9], while others have found that inclusive fitness is suitable for evaluating convergence stability but not for evolutionary stability [10,11].
		is a function of the resident strategy z and of the mutant strategy, whose deviation from z is denoted δ.
		Local stability conditions are given in terms of the first- and second-order derivatives of the fitness measure [4-6].
	www.biomedcentral.com /1471-2148/3/22 (6069 words)

	Shirky: Fame vs Fortune: Micropayments and Free Content
		This strategy doesn't work, because the act of buying anything, even if the price is very small, creates what Nick Szabo calls mental transaction costs, the energy required to decide whether something is worth buying or not, regardless of price.
		It's also a strategy that continues to work if everyone is using it, because in such an environment, anyone who begins charging for their work will be at a disadvantage.
		So offering free content is not just an evolutionary stable strategy, it is a strategy that improves with time, because the more free content there is the greater the advantage it has over for-fee content.
	shirky.com /writings/fame_vs_fortune.html (2022 words)

	Highbeam Encyclopedia - Search Results for Evolutionarily
		The evolutionarily oldest part of the cerebellum, present even in fishes, consisting of a pair of small irregular structures (flocculi) joined in the middle by a node (1) or nodulus and separated by a deep fissure from the back of the cerebellum, connected to the vestibular...
		Unlike evolutionarily advanced fishes, it has a fine-grained hide, with very reduced scalation, a mostly cartilaginous skeleton, upturned tail fins, and a mouth set well back on the underside of the head.
		Return of the Guy: Men were pronounced economically and evolutionarily finished in the late 1990s.
	www.encyclopedia.com /SearchResults.aspx?Q=Evolutionarily (932 words)

	Dynamic Stability in Perturbed Games
		The effect that exogenous mistakes, made by players choosing their strategies, have on the dynamic stability for the replicator dynamic is analyzed for both asymmetric and symmetric normal form games.
		Through these perturbed games, the dynamic solution concept of limit asymptotic stability is motivated by insisting that such solutions be asymptotically stable for all sufficiently small perturbations (a robustness property).
		Limit asymptotically stable sets are introduced that generalize other set-valued solution concepts such as the ``strict equilibrium set'' and the ``ES set'' for asymmetric and symmetric normal form games respectively.
	www.iue.it /Personal/Schlag/papers/dynamic.html (215 words)

	Gene Expression: Evolutionarily Stable Strategies and the Strategy Set
		As usually defined, an ESS is a strategy such that, if all the members of a population adopt it, no mutant strategy can invade (John Maynard Smith, Evolution and the Theory of Games, p.
		Payoffs for the matrix of pure strategies are estimated from observations.
		The essential point is that the ESS is always relative to a given strategy set and payoffs.
	www.gnxp.com /MT2/archives/002161.html (589 words)

	The relationship between measures of fitness and time scale in evolution
		The assumption that populations that have reached a stationary state will be composed mainly of types with the highest number of offspring only applies to systems where the instantaneous change in frequency is sufficient to determine the long-term composition of the population.
		In the model, the evolutionarily stable type is out-competed in the short term by seemingly fitter mutants.
		This measure indicates the evolutionarily stable type in such cases, and it can be used to quantify the time scale at which selection acts against the mutants with short-term advantage.
	www.swiss.ai.mit.edu /~rauch/timescale_prl (2413 words)

	Please go to: http://www-personal.umich.edu/~kruger/
		With only one interaction, the evolutionarily stable strategy is to defect.
		Tit-for-tat (cooperate on first move, than mirror actions of the other) will be an evolutionarily stable strategy against defection if the probability for future interaction is sufficiently high.
		Those pursing the tit-for-tat strategies and unconditional altruists will be equally viable in a closed population.
	www-personal.umich.edu /~kruger/ep5.html (831 words)

	urticator.net - No Pure Strategy Is Stable
		Now, I know about “tit for tat” (see Evolutionarily Stable Strategies), and am quite fond of it, but I thought that description was a bit strong.
		If, for example, the pure strategy is nice, i.e., never the first to defect, then its behavior in response to a defection is never explored, and any other nice strategy can invade it—just as the strategy that always cooperates can invade “tit for tat”.
		The original strategies all do equally well when they play each other; the only thing that distinguishes them is how well they do when they play the mutants … and, as it happens, one can always find mutants that will make the original pure strategy lose.
	www.urticator.net /essay/4/427.html (670 words)

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