Every society has an energy profile, that is, an array of energy sources, ranging in complexity from human power to nuclear fusion, that can be ranked according to their relative importance to that society. From about 4000 BE onward, animal muscle power becomes integrated into the energy profiles of many societies. The forms this integration takes include riding, carrying burdens, pulling wheeled vehicles and sleighs, operating mills and irrigation devices, and pulling plows, threshing sleds,...

Every society has an energy profile, that is, an array of energy sources, ranging in complexity from human power to nuclear fusion, that can be ranked according to their relative importance to that society. From about 4000 BE onward, animal muscle power becomes integrated into the energy profiles of many societies. The forms this integration takes include riding, carrying burdens, pulling wheeled vehicles and sleighs, operating mills and irrigation devices, and pulling plows, threshing sleds,...