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,
Evolution of the eye of their owners. They vary in their visual acuity, the range of wavelengths they can detect, their sensitivity in low light, their ability to detect motion or to resolve objects, and whether they can discriminate colours. In 1802, philosopher William Paley called it a miracle of "design". Charles Darwin himself wrote in his "Origin of Species", that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". However, he went on that despite the difficulty in imagining it, its evolution was perfectly feasible: ...if numerous gradations from a simple and imperfect eye