Shaded areas are proportional to the frequencies of different alleles (colors) in a population. (A) Escalating arms races, where epidemics of cheating and/or resistance sweep through populations, (B) Stalemates, where cheaters invade but neither fix nor become lost from the population, resulting in endemic cheating, (C) Mutation-selection balance, where new mutations that produce cheating behaviors are continually introduced into a population, but selection removes them.