conventional and alternative mating behaviours arise through sexual selection. more specifically, varying levels of reproductive success will select for phenotypes and strategies that maximize an animal's chance of obtaining a mate. as a result, certain animals successfully use a conventional mating strategy while others employing this strategy fail to obtain mates. over time, phenotypic variance arises both between and within the sexes, with males exhibiting greater diversity in phenotype. the resulting variance in male fitness creates a niche in which alternative strategies may develop, such as sneaking to obtain a mate. the alternative behaviours persist as part of this polymorphism, or variety of phenotypes, because the average fitness of unconventional males equals the average reproductive success of conventional males.