the development of one or more cultures from simpler to more complex forms. The subject may be viewed as a unilinear phenomenon that describes the evolution of human behaviour as a whole, or it may be viewed as a multilinear phenomenon, in which case it describes the evolution of individual cultures or societies (or of given parts of a culture or society).

Unilinear cultural evolution was an important concept in the emerging field of anthropology during the 18th and 19th centuries but fell out of favour in the early 20th century. Scholars began to propagate theories of multilinear cultural evolution in the 1930s, and these neoevolutionist (neoevolutionism) perspectives continue, in various forms, to frame much of the research undertaken in physical anthropology and archaeology, the branches of anthropology (anthropology) that focus on change over time.

This Enlightenment notion that there was, in fact, a “natural order” derived from the philosophers of ancient Greece, who had described the world as comprising a Great Chain of Being—a view in which the world is seen as complete, orderly, and susceptible to systematic analysis. As a result, scholarship during the Enlightenment emphasized categorization and soon produced various typologies (typology) that described a series of fixed stages of cultural evolution.

The English philosopher Herbert Spencer (Spencer, Herbert) was among the first to work out a general evolutionary scheme that included human societies from across the globe. He held that human cultures evolved from less-complex “species” to those that were more so: people at first lived in undifferentiated hordes; then developed social hierarchies with priests, kings, scholars, workers, and so forth; and later accumulated knowledge that was differentiated into the various sciences. In short, human societies evolved, by means of an increasing division of labour, into complex civilizations.

This passage is from Morgan's masterwork Ancient Society (1877), in which he also described seven stages of cultural evolution: lower, middle, and upper savagery; lower, middle, and upper barbarism; and civilization. He supported his ideas by citing contemporary societies characteristic of each stage except lower savagery, of which there were no extant examples.

Morgan's work was very widely read and became the basis for further developments in anthropology, perhaps most notably its emphasis on cross-cultural comparison and its preoccupation with the mechanisms of change. His work underlay debates on matters, such as the relative importance of technological innovation (versus diffusion), that were of serious concern for the remainder of the 19th century and persisted well into the 20th. However, although it is considered important in the history of anthropology, Morgan's work, and indeed unilineal cultural evolution as a whole, no longer hold credence in the field.

Boas and several generations of his students—including A.L. Kroeber (Kroeber, A.L.), Ruth Benedict (Benedict, Ruth), and Margaret Mead (Mead, Margaret)—turned completely away from broad generalizations about culture and concentrated on fieldwork among traditional peoples, harvesting a great variety of facts and artifacts as empirical evidence of cultural processes within existing societies. The creation of encyclopaedic lists of cultural traits and changes therein led to the development of “culture histories” and dominated American anthropology for the first half of the 20th century. The culture history movement so influenced anthropology that grand theories of “Man” became far less common than in the past.

By mid-century, however, a number of American anthropologists, including Leslie A. White (White, Leslie A.), Julian H. Steward (Steward, Julian), Marshall D. Sahlins, and Elman R. Service (Service, Elman Rogers), had revived theoretical discussions regarding cultural change over time. They rejected universal stages outright, instead conceptualizing cultural evolution as “multilinear”—that is, as a process consisting of a number of forward paths of different styles and lengths. They posited that while no specific evolutionary changes are experienced by all cultures universally, human societies do generally evolve or progress. They further suggested that the primary mechanism for such progress involved technological breakthroughs that make societies more adaptable to and dominant over the environment; technology, in this case, was quite broadly conceived, and included such developments as improvements in tool forms or materials (as with the transition through the Stone, Bronze, and Iron ages and later the Industrial Revolution), transportation (as from pedestrian to equestrian to motorized forms), and food production (as from hunting and gathering to agriculture). Proponents of multilinear evolution hold that only in this sense can the whole of world culture be viewed as the product of a unitary process.