It is possible for polymorphism to be maintained in a population by frequency-dependence without any load at all.

With frequency-dependent selection, a rare genotype is relatively favored by selection and it will increase in frequency; as it becomes commoner, its fitness decreases and there may come a point at which it is no longer favored. Thus an equilibrium frequency is reached and the genotype is maintained in the population. Batesian mimicry among butterflies, such as Papilio glaucus opposite, is a good example of frequency-dependent selection.