Attempts are being made by Parsons and others to revive a theory of social evolution, stressing the continuity of sociology with biology, in the manner of Spencer; this is related to the current concern with the problems of developing countries. Spencer's theory is analysed. His main insight was into the process of evolution-differentiationl- and his explanation of the mechanism-adaptation to the environment-tended to circtularity. His theory was, moreover, highly anti-historical, for he sought a universal mechanism. Parsons, though aspiring to be more Darwinian, repeats these errors, even when, as in his complaint of the unilinearity of Spencer's system, claiming to correct them. The necessitarian optimism of Spencer fulfilled a function in European societies already undergoing industrialization; it created order and confidence by suggesting that the ends to which society was moving were scientifically grounded. Today we use sociology to help provide means to industrialization in the developing countries. Consequently we need to analyse unique historical situations, not provide a universal mechanism; that, which social evolution promises, is both impossible and useless.