a1 Department of Near Eastern Studies Princeton University
The degree of development (or, if you prefer, material civilization) of any society is set by the size of its surplus (the total amount it produces minus the amount needed for the bare subsistence of the population) and the uses to which the surplus is put. In Emerson's wise words, “The question of history is what each generation has done with its surplus produce. One bought crusades, one churches, one villas, one horses and one railroads.” The size of the surplus is, in turn, determined by four factors: the amount of energy available to the society, the society's technology, the mix of its economy, and the size of its population. Until comparatively recently, energy was, with the important exception of sailing ships, provided exclusively by human or animal power.1 Two important steps forward were the invention of the watermill and that of the windmill; their development will be discussed later. Nevertheless, it has been estimated that until the Industrial Revolution, some 80–85 percent of total energy was provided by plants, animals, and people.2 This means that the basic factors determining the amount of energy available to a society were the amount of land (arable, pasture, and woodland) it had at its disposal and the land's productivity. Land “was not simply the principal source of food for the population [the other being the seas and rivers] but also virtually the sole source of the raw materials used in industrial production”—fibers, hides, hair, wood, and so forth; almost all industrial workers were engaged in processing agricultural materials.