Sociocultural evolution justify new policies such as eugenics. Most 19th-century and some 20th-century approaches aimed to provide models for the evolution of humankind as a single entity. However, most 20th-century approaches, such as multilineal evolution, focused on changes specific to individual societies. Moreover, they rejected directional change (i.e. orthogenetic, teleological or progressive change). Most archaeologists work within the framework of multilineal evolution. Other contemporary approaches to social change include neoevolutionism, sociobiology, dual inheritance theory, modernisation theory and postindustrial theory. In his seminal 1976 book "The Selfish Gene", Richard Dawkins wrote that "there are some examples of cultural evolution in birds and monkeys,
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,