Cottrell, William Frederick
William Frederick Cottrell (1903-1979), an American sociologist, developed a general theory of social and economic change based on changes in energy sources and their conversion technologies. In Energy and Society (1955), Cottrell describes the evolution of human culture in terms of energy. He is the first social scientist to identify the importance of the net energy return, or the energy surplus, delivered by a society’s energy system. Cottrell also emphasized the importance of energy transitions, such as the shift from animate energy sources (human labor and draft animals) to inanimate energy sources and their associated converters (fossil fuels, steam, and the internal combustion engine).