The evolution of costly mate preferences. I. Fisher and biased mutation

Fisher's runaway process is the standard explanation of the evolution of exaggerated female preferences. But mathematical formulations of Fisher's process (haploid and additive diploid) show it cannot cause stable exaggeration if female preference carries a cost. At equilibrium female fitness must be maximized. Evolutionary stable exaggeration of female preference can be achieved if mutation pressure on the male character is biased, ie mutation has a directional effect. At this equilibrium female fitness is not maximized. -from Authors