Evolution of Energy Capture Throughout Human History
Discussion
"In a widely reprinted diagram (Graph 3) originally published in Scientific American magazine in 1971, geoscientist Earl Cook of Texas A&M University offered rough estimates of typical p er person energy capture among hunter-gatherers, early agriculturalists (by which he meant the farmers of southwest Asia around 5000 BCE), advanced agriculturalists (those of northwest Europe around 1400 CE), industrial folk (west Europeans around 1860), a nd the “technological” societies of North America and Western Europe in the 1970s CE. He divided each score into the four categories of food (including animal feed), home and commerce, industry and agriculture, and transportation. This diagram has become a regular point of departure for world historians discussing of the history of energy capture, and I have followed in this tradition.
Earl Cook’s (1971) diagram of energy consumption at different stages of social development Cook’s food/nonfood energy distinction is fundamental. Human consumption of food energy is tightly constrained: if it falls much below an average of 2,000 kilocalories per person per day (kcal/cap/day) for any length of time, people will become unable to work, lose body functions, and die prematurely. If it stays much above 3,000 kcal/cap/day for any length of time, people will become obese, suffer serious health complications, and again die prematurely. (Nutritionists normally use “calories” to describe what physicists would call nutritional kilocalories, and the caloric content listed in “Nutrition facts” on food packaging actually refers to kilocalories.) Consumption of food energy has changed over time in part because people have shifted back and forth between “cheap” calories such as grains and “expensive” calories such as meat (as a rough measure, it takes about ten calories of feed to grow one calorie of meat). Meat-rich 21st century diets typically represent about 10,000 kcal/cap/day. Consumption of energy in non d forms, however, has changed much more dramatically.
Most hunter-gatherers consume rather few nonfood calories: they need biomass for cooking fuel, clothes, weapons, baskets, and personal ornaments, but typically have only very simple shelters and no substantial material goods.
Peasant societies normally have much more substantial homes and a wide range of artifacts, and modern industrial societies of course produce nonfood goods in extraordinary quantities. Total (i.e., food + nonfood) energy capture i 4,000n the simplest tropical hunter-gatherer societies can be as low as 5,000 kcal/cap/day; in the contemporary USA it has reached 230,000 kcal/cap/day. Through most of history per capita nonfood energy capture has tended to rise, but people have had few ways to convert nonfood calories into food. As a result, the difficulty of increasing food calories has been the major brake on rising living standards. Thomas Malthus already recognized this in his Essay on the Principle of Population : “ It should be remembered always,” he wrote, “that there is an essential difference between food and those wrought commodities, the raw materials of which are in great plenty. A demand for these last will not fail to create them in as great a quantity as they are wanted. The demand for food has by no means the same creative power” (Malthus 1798: Chapter 5). Even in prehistoric times nonfood energy could slightly loosen the constraints on food supply, for instance by providing manure (e.g., Bogaard et al. 2007) or by improving transport that could move food from places where it was plentiful to those where it was scarce and giving them fuel to process it, but only since the nineteenth century CE (ironically, beginning during Malthus’ lifetime) have transport, processing, fertilizers, and scientific interventions revolutionized the food supply, relentlessly increasing stature, life expectancy, and health (e.g., Fogel 2004).
Despite its prominence in Malthus’ and Cook’s work, social scientists interested in long term economic hi story regularly ignore the food/nonfood calories distinction and, focusing solely on food, conclude that between the invention of agriculture more than 10,000 years ago and the industrial revolution 200 years ago not very much happened. One of the most widely cited recent discussions explicitly suggests that “the average person in the world of 1800 [CE] was no better off than the average person of 100,000 BC” (Clark 2007: 1). This is mistaken. As Malthus recognized, if good weather or technological/organizational advances raised food output, population did tend to expand to consume the surplus, forcing people to consume fewer and cheaper food calories; but despite the downward pressure on per capita food supply, increases in non have, in the long run, steadily accumulated. Cook suggested that while typical hunterfood energy capture gatherers captured just 2,000 kcal/cap/day of nonfood energy, early farmers raised this to 8,000 kcal/cap/day, and advanced preindustrial farmers to 20,000 kcal/cap/day. My own reconstruction suggests that in the long run (passing over several periods of collapse), nonfood energy capture rose steadily across the thirteen — millennia after the end of the ice age around 12,700 BCE, until in Roman Italy the core of the most advanced ancient agrarian empire — it may have reached 25,000 kcal/cap/day. This seems to have been the ceiling on what was possible in a preindustrial society, corresponding to the boundary between what E. A. Wrigley (1988) called advanced organic economies and fossil fuel economies. For nearly 2,000 years agrarian empires pressed against this ceiling without breaking it; only in the 18th century, when British entrepreneurs learned to convert the energy released by burning coal from heat into motion, did nonfood energy capture increase so much that it could in turn be converted into food calories, freeing humans from the Malthusian trap."