incredibly popular figure in the 1870s, particularly in the United States. Authors such as Edward L. Youmans, William Graham Sumner, John Fiske, John W. Burgess, Lester Frank Ward, Lewis H. Morgan (1818–1881) and other thinkers of the gilded age all developed theories of social evolutionism as a result of their exposure to Spencer as well as to Darwin. In his 1877 classic Ancient Societies, Lewis H. Morgan, an anthropologist whose ideas have had much impact on sociology, differentiated between three eras: savagery, barbarism and civilization, which are divided by technological inventions, like fire, bow, pottery in the savage era, domestication of animals, agriculture, metalworking in the barbarian era and alphabet and writing in the civilization era. Thus Morgan drew a link between social progress and technological progress. Morgan viewed technological progress as a force behind social progress, and held that any social change—in social institutions, organizations or ideologies—has its beginnings in technological change. Morgan's theories were popularized by Friedrich Engels, who based his famous work The Origin of the Family, Private Property and the State on them. For Engels and other Marxists this theory was important, as it supported their conviction that materialistic factors—economic and technological—are decisive in shaping the fate of humanity. Edward Burnett Tylor (1832–1917), a pioneer of anthropology, focused on the evolution of culture worldwide, noting that culture is an important part of every society and that it is also subject to a process of evolution. He believed that societies were at different stages of cultural development and that the purpose of anthropology was to reconstruct the evolution of culture, from primitive beginnings to the modern state. Anthropologists Sir E.B. Tylor in England and Lewis Henry Morgan in the United States worked with data from indigenous people, who (they claimed) represented earlier stages of cultural evolution that gave insight into the process and progression of evolution of culture. Morgan would later have a significant influence on Karl Marx and on Friedrich Engels, who developed a theory of sociocultural evolution in which the internal contradictions in society generated a series of escalating stages that ended in a socialist society (see Marxism). Tylor and Morgan elaborated the theory of unilinear evolution, specifying criteria for categorising cultures according to their standing within a fixed system of growth of humanity as a whole and examining the modes and mechanisms of this growth. Theirs was often a concern with culture in general,