Re: Evolutionarily Stable Strategies (ESSs)

From: Stevan Harnad (
Date: Sat Oct 11 1997 - 22:32:39 BST

> From: Tim Lyons <>
> in "the selfish gene" dawkins defines an evolutionarily stable
> strategy (ESS) as "a strategy which if most members of a population
> adopt it cannot be bettered by an alternative strategy." it is easy
> enough to work out how this comes about if the ESS is to always do
> one particular thing in a particular given situation.
> this is the way i see an ESS coming into being where it is necessary
> that different strategies are used in a certain ratio.
> 1 in any given situation an individual member of a population
> has a variety of ways in which it can react and it chooses one.
> 2 different actions (or strategies) are more or less
> successful than others.
> 3 as the species evolves the more successful
> strategies will tend to become more common, and less
> successful strategies, less common.
> 4 for each possible set of strategies for any given situation,
> a stable state will evolve where there will be a certain ratio of the
> different strategies. either due to there being that ratio of
> individuals who always react in the necessary ways (unlikely), or the
> total number of the uses of the particular strategies across the
> population is in that ratio. any individual who uses the necessary
> strategies in the correct ratio will in theory, all things being
> equal, be more successful than one who does not.
> this is of course fairly academic as there will always be a degree of
> variation in any population which will lead certain individuals to
> engage in certain strategies other than the ESS. for instance it will
> be more advantageous for a stronger than average individual to use a
> more aggressive strategy than the ESS.

Tim, this is too abstract; it doesn't give the flavour of strategy,
stability, or evolution. But you are right that actual ESS explanations
tend to simplify things.

At the very least, you have to be specific enough to indicate what kind
of end the strategy is a means of attaining, and why it's attained
doing one strategy rather than another; and because an ESS is usually a
social trait, you have to specify how it relates to other (competing)
organisms ends and means (or rather, those of their selfish genes.

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