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Multilineal evolution is a 20th-century social theory about the evolution of societies and cultures. It is composed of many competing theories by various sociologists and anthropologists. This theory has replaced the older 19th century set of theories of unilineal evolution.
When critique of classical social evolutionism became widely accepted, modern anthropological and sociological approaches have changed to reflect their responses to the critique of their predecessor. Modern theories are careful to avoid unsourced, ethnocentric speculation, comparisons, or value judgements; more or less regarding individual societies as existing within their own historical contexts. These conditions provided the context for new theories such as cultural relativism and multilineal evolution.
By the 1940s cultural anthropologists such as Leslie White and Julian Steward sought to revive an evolutionary model on a more scientific basis, and succeeded in establishing an approach known as the neoevolutionism. White rejected the opposition between "primitive" and "modern" societies but did argue that societies could be distinguished based on the amount of energy they harnessed, and that increased energy allowed for greater social differentiation. Steward on the other hand rejected the 19th century notion of progress, and instead called attention to the Darwinian notion of "adaptation," arguing that all societies had to adapt to their environment in some way.
The anthropologists Marshall Sahlins and Elman Service wrote a book, Evolution and Culture, in which they attempted to synthesize White's and Steward's approaches. Other anthropologists, building on or responding to work by White and Steward, developed theories of cultural ecology and ecological anthropology. The most prominent examples are Peter Vayda and Roy Rappaport. By the late 1950s, students of Steward such as Eric Wolf and Sidney Mintz turned away from cultural ecology to Marxism, World Systems Theory, Dependency theory and Marvin Harris's Cultural materialism.
Today most anthropologists continue to reject 19th century notions of progress and the three original assumptions of unilineal evolution. Following Steward, they take seriously the relationship between a culture and its environment in attempts to explain different aspects of a culture. But most modern cultural anthropologists have adopted a general systems approach, examining cultures as emergent systems and argue that one must consider the whole social environment, which includes political and economic relations among cultures. There are still others who continue to reject the entirety of the evolutionary thinking and look instead at historical contingencies, contacts with other cultures, and the operation of cultural symbol systems. As a result, the simplistic notion of 'cultural evolution' has grown less useful and given way to an entire series of more nuanced approaches to the relationship of culture and environment. In the area of development studies, authors such as Amartya Sen have developed an understanding of 'development' and 'human flourishing' that also question more simplistic notions of progress, while retaining much of their original inspiration.