Well-meaning critics struggled to conceal their perplexity, behind which laid a thick wall of denial. The second part of “Descent of Man” published in 1871 contained Charles Darwin's treatise on “sexual selection”, which presented perhaps his greatest failure. Darwin was confronted with the problem of not believing that nature, which was literally exploding with variety and diversity, could be explained solely with the aid of “natural selection”. To resolve this conflict he came up with the theory of “sexual” selection, making the female eye the agent of evolution. “Female choice” as he called it, was in no only way solely obligated to follow a commitment to strength and guaranteed survival; the female interest essentially followed another principle, one that could be described as the desire for variation. This meant that Darwin was defining nature, to a certain extent, as a history of erotic form – or even art. In regarding the bodies of animals as self-produced images, he defined his second pillar of evolution as an astonishing pictorial theatre which arose out of the interplay of the female eye in the search for variation and the readiness of the male to mutate.
Fellow naturalists like Alfred R. Wallace were so dismissive of Darwin's theory because they could not accept the existence of a variational drive independent of the pressure to conform to the environment.
Evolutionary biology has never managed to shake off this discomfort, even if the theory of sexual selection continues to be picked up by outsiders and has been cautiously integrated into and developed by the mainstream. The misgivings were also culturally determined. Unlike Darwin's 1859 treatise “The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life” which hit a nerve at a time when the struggle for survival was being unleashed under the conditions of burgeoning capitalism, his concept of sexual selection inadvertently struck at the neurotic core of the Victorian obsession with controlling drives. This provoked a resistance whose unacknowledged psychological roots made it virtually invincible.