The theory of organic evolution extended to social life, religion, law, morality, marriage, the family, ethics, etc.
According to this theory (known as that of unilinear cultural evolution) there is a rigid evolutionary development in all man's higher cultural and institutional life, each step presupposing one of a definitely lower type.
Among proponents of the theory are Sir John Lubbock, J. F. McLennan, Herbert Spencer, E. B. Taylor, J. G. Frazer, E. Crowley, L. H. Morgan, and Charles Letrouneau.
Their arguments, though still quoted in many text-books of sociology, are rejected by most later students of ethnology and anthropology.
In particular the assumptions that the monogamous family developed through a series of "upward stages" out of a condition of promiscuity, and that the property sense grew out of its antithesis, communism, are now generally abandoned.
The Evolutionary School is thus gradually being replaced by the better-informed Historical School.
New Catholic Dictionary