Diploid models of the handicap principle.

"Fisherian" models of sexual selection by female choice assume that females prefer male characters which are initially advantageous or neutral; character and preference then spread through the population. Once female preference has evolved to a higher frequency, the male character can become more extreme and disadvantageous by the action of some force such as the "super-normal stimulus". By contrast, the "handicap principle" of sexual selection proposes that females should prefer more extreme, disadvantaged males: males who survive the disadvantage of the "handicap" must be fitter in other respects. Previous models of various forms of the "handicap principle" have shown that it is very unlikely to work as an alternative to the "Fisherian process". However, recent haploid models have shown that a "condition-dependent handicap" might evolve. Diploid models show that the "condition-dependent handicap" model does not work. Models of "handicaps" operating together with the "Fisherian process" are also presented. It is inferred that "Fisherian" models are more likely than "handicap" models to account for the evolution of male sexual ornaments, although a "handicap" mechanism may aid the operation of the "Fisherian process".