Every social system is a functioning entity. That is, it is a system of interdependent structures and processes such that it tends to maintain a relative stability and distinctiveness of pattern and behaviour as an entity by contrast with its - social or other - environment, and with it a relative independence from environmental forces. It "responds", to be sure, to the environmental stimuli, but is not completely assimilated to its environment, maintaining rather an element of distinctiveness in the face of variations in environmental conditions. To this extent it is analogous to an organism
Parsons (1942) "Propaganda and Social Control". in: Parsons (1954) Essays in sociological theory, p. 143