Peacoke hypotheses

Multiple hypotheses attempt to explain the evolution of female choice. Some of these suggest direct benefits to females, such as protection, shelter, or nuptial gifts that sway the female's choice of mate. Another hypothesis is that females choose mates with good genes. Males with more exaggerated secondary sexual characteristics, such as bigger, brighter peacock trains, tend to have better genes in the peahen's eyes.[6] These better genes will directly benefit her offspring, as well as her fitness and reproductive success. Runaway selection also seeks to clarify the evolution of the peacock's train. In runaway sexual selection, linked genes in males and females code for sexually dimorphic traits in males, and preference for those traits in females.[7] The close spatial association of alleles for loci involved in the train in males, and for preference for more exuberant trains in females, on the chromosome (linkage disequilibrium) causes a positive feedback loop that exaggerates both the male traits and the female preferences. Another hypothesis is sensory bias, in which females have a preference for a trait in a non-mating context that becomes transferred to mating. Multiple causality for the evolution of female choice is also possible. Work concerning female behavior in many species of animals has sought to confirm Darwin's basic idea of female preference for males with certain characteristics as a major force in the evolution of species.[8] Females have often been shown to distinguish small differences among potential mates, and to prefer mating with individuals bearing the most exaggerated characters.[9] In some cases, those males have been shown to be more healthy and vigorous, suggesting that the ornaments serve as markers indicating the males' abilities to survive and, thus, their genetic qualities.