Modification of genetic constraints on frequency-dependent selection

The prediction of phenotypic equilibrium states through reasoning about evolutionarily stable states (ESS's) is commonplace in evolutionary biology. When there is a specific genetic system underlying the transmission of phenotypes, however, genetic constraints may prevent the realization of phenotypic equilibria. With two-strategy games and a one-locus genetic system, the direction of selection is always toward an ESS, and all stable genetic equilibria that are not ESS's (non-ES equilibria) can be characterized as being as close to the ESS as the genetic system allows, at least locally. Starting from these non-ES equilibria, a series of computer simulations shows that the evolution of modifier genes at a second locus is expected to move the population closer to the ESS, although there are counterexamples. With multiple-strategy games, the genetic constraints are much more complex. It is not generally the case that genetic equilibria are "close' to the ESS in some sense. -Authors