Local Replicator Dynamics: A Simple Link Between Deterministic and Stochastic Models of Evolutionary Game Theory |
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Authors: | Christian Hilbe |
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Institution: | Faculty of Mathematics, University of Vienna, Nordbergstrasse 15, 1090 Vienna, Austria. christian.hilbe@univie.ac.at |
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Abstract: | Classical replicator dynamics assumes that individuals play their games and adopt new strategies on a global level: Each player
interacts with a representative sample of the population and if a strategy yields a payoff above the average, then it is expected
to spread. In this article, we connect evolutionary models for infinite and finite populations: While the population itself
is infinite, interactions and reproduction occurs in random groups of size N. Surprisingly, the resulting dynamics simplifies to the traditional replicator system with a slightly modified payoff matrix.
The qualitative results, however, mirror the findings for finite populations, in which strategies are selected according to
a probabilistic Moran process. In particular, we derive a one-third law that holds for any population size. In this way, we
show that the deterministic replicator equation in an infinite population can be used to study the Moran process in a finite
population and vice versa. We apply the results to three examples to shed light on the evolution of cooperation in the iterated
prisoner’s dilemma, on risk aversion in coordination games and on the maintenance of dominated strategies. |
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