The theoretical school of Functionalism considers a culture as an interrelated whole, not a collection of isolated traits. The Functionalists examined how a particular cultural phase is interrelated with other aspects of the culture and how it affects the whole system of the society. The method of functionalism was based on fieldwork and direct observations of societies. The anthropologists were to describe various cultural institutions that make up a society, explain their social function, and show their contribution to the overall stability of a society. (Source)
This theory didn't take cultural change into account, so it was quite short-lived. It began in the 1920s by Anthropologists in the field, however, after the massive culture change of post-world war two, it quickly died out. However, it is still used as part of the cultural analysis
Three important Anthropologists who contributed to this theory are, Bronislaw Malinowski, Alfred Radcliffe-Brown and, Edward Evans-Pritchard.
Malinowski theorized "... that individuals have physiological needs and that social institutions develop to meet these needs. There are also culturally derived needs and four basic "instrumental needs" (economics, social control, education, and political organization), that require institutional devices." (Source)
Whereas Radcliffe-Brown thought that "... a society is a system of relationships maintaining itself through cybernetic feedback, while institutions are orderly sets of relationships whose function is to maintain the society as a system." Hence, he is known more as a structuralist-functionalist. Source)
Evans-Pritchard believed "... the need for the inclusion of history in the study of social anthropology." He actually moved out of the functionalist theoretical framework later on in his career and became a humanist. Source)
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