A concept associated with evolutionary theories of history and with structural functionalism. Societies are seen as moving from the simple to the complex via a process of social change based on structural differentiation. The process may be imagined, in its simplest form, as an amoeba dividing, redividing, then redividing again. So-called simple societies are tribal societies where everything happens within and through the kinship system. In modern complex societies there are separate institutions of education, work, government, religion, and so forth, while the family now has more specific and limited roles—such as early socialization. Differentiation involves the increasing specialization of different subsystems and institutions within the society.
A classic statement may be found in the work of the Israeli comparative and historical sociologist Shlomo N. Eisenstadt (see especially ‘Social Change, Differentiation and Evolution’, American Sociological Review, 1964), now unfashionable, mainly because of its association with the modernization theory of the 1960s. This neglect is probably unwarranted, since Eisenstadt offers a sophisticated theory of change that goes a long way beyond traditional evolutionary theories, and represents the most systematic attempt yet to deploy the concept of structural differentiation in substantive analyses (as for example in Modernization, Protest and Change, 1967, and Revolution and the Transformation of Societies, 1978).
Talcott Parsons sees the process as involving three stages: a process of differentiation; a process of adaptation and reintegration; and, finally, the establishment of a more general system of values which holds the more complex society together. The impetus towards differentiation comes from the need for a society to adapt to its physical and social environment. The basic evolutionary idea can be found in Herbert Spencer, is developed and applied to a particular instance by Neil Smelser (Social Change in the Industrial Revolution, 1959), and expounded at the most general level by Parsons himself (Societies: Evolutionary and Comparative Perspectives, 1966).
Evolutionary theories such as this have been much criticized by sociologists during the past two decades. Anthony Giddens, for example, in The Constitution of Society (1984) argues that simple societies are actually not simple at all, and that the mechanism of adaptation is too vague and general to explain social change.