Re: Evolutionarily Stable Strategies (ESSs)

From: Tim Lyons (
Date: Mon Oct 06 1997 - 16:49:38 BST

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.

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