In the 19th century, evolutionism was a current of thought based on a biological analogy, but distinguished from Darwinian theory by its deterministic nature. Darwin's general theory of evolution claims that natural species evolve through variation and natural selection, a process that is not necessarily progressive. However, in the evolutionary theory espoused by Victorian social scientists, human societies were bound to improve, change was progressive, and led to further civilization and moral improvement of human society. Such theories were central to the 19th-century approach to society and political life. They underpinned colonialism and are still deeply entrenched in Western thought. Kenneth Bock's essay on ‘Theories of Progress, Development, Evolution’ (in T. Bottomore and R. Nisbet (eds.), A History of Sociological Analysis, 1979) gives a good history and overview.
Although evolutionary theory in sociology is attributed to Herbert Spencer, it is clear that it was taken for granted by writers as diverse as Karl Marx, Friedrich Engels, Émile Durkheim, and V. Gordon Childe. The fact that it can be traced in the work of both radical and conservative theorists is indicative of the profound cultural importance of evolutionism for Western thought. See also change, social; Darwinism; evolutionary universals; Frazer, Sir James George; matriarchy; Morgan; Parsons; progress; social anthropology.