In the social sciences, functionalism originally attempted to explain social institutions as collective means to fill individual biological needs; later it came to focus on the ways social institutions fill social needs, especially social solidarity. Functionalists argue that social institutions are functionally integrated to form a stable system, and a change in one institution will precipitate a change in other institutions. It was one of the first twentieth century anthropological theories, until it was superseded by structural-functionalism. Structural-functionalism takes the view that society consists of parts (e.g. police, hospitals, schools, and farms), each of which has its own function. Structural-functionalism was the dominant perspective of cultural anthropologists and rural sociologists between World War Two and the Vietnam War. Along with conflict theory and interactionism, functionalism is one of the three major sociological traditions.