Unit of selection and Confirmation of Evolutionary Theory" provides a basic "philosophical" introduction to the debate. Below, cases of selection at the genic, cellular, individual and group level from within the multi-level selection perspective are presented and discussed. George C. Williams in his influential book "Adaptation and Natural Selection" was one of the first to present a gene-centered view of evolution with the gene as the unit of selection, arguing that a unit of selection should exhibit a high degree of permanence. Richard Dawkins has written several books popularizing and expanding the idea. According to Dawkins, genes cause phenotypes and a gene is
The Evolution of Beauty preeminent. Prum proceeds to apply the principle of aesthetic evolution as an independent force in human evolution. Prum indicates that Darwin recognizing difficulties in the theory of natural selection advanced the view that sexual selection is an additional force in evolution and presented this argument in "The Descent of Man". Alfred Russel Wallace, St. George Mivart and other early evolutionists helped to elevate natural selection as the only force in evolution and delegated sexual selection to a subsidiary role. It was argued that sexual selection was based on recognition of markers of survival fitness, so that, for instance in birds,