El origen del hombre
There are several evolutionary explanations for the presence of ornaments. Darwin was the first to correctly hypothesize that sexual selection by female choice was responsible for the evolution of elaborate plumage and remarkable displays in male birds such as the quetzal and the sage grouse. Sexual selection is selection acting on variation among individuals in their ability to obtain access to mating partners. In his book, The Descent of Man, and Selection in Relation to Sex written in 1871, Darwin was perplexed by the elaborate ornamentation that males of some species have because they appeared to be detrimental to survival and have negative consequences for reproductive success. Darwin proposed two explanations for the existence of such traits: these traits are useful in male-male combat or they are preferred by females.