In 1940, Buckminster Fuller was the first to use the term "energy slave" in a map in "Fortune". He calculated the yield of an energy slave by taking the energy from minerals and water consumed by industry and dividing it by the energy provided by a human being. For a world population of just over two billion people (2 125 000 000 exactly), Fuller estimates that there are thirty-six billion energy slaves at the time, representing 17 per capita. In 1940, these energy slaves were not equitably distributed around the world: the United States owned twenty billion of them (54% of the world total). In 1950, Fuller revised his calculations upwards and estimated that, on average, each human holds 38 energy slaves.