Leigh Kimmel’s Reviews > Energy and Civilization: A History > Status Update

The limits of muscle power -- including the fact that you can't turn the prime movers on and off at need, so you have to feed and shelter them all year even if you only need them a few months. The use of various simple machines -- wheels, levers, etc. -- to gain more work out of the same amount of effort.

As farming becomes more intensive, draft animals need more and better food -- putting them in competition with the humans they're working for. Improvements in tools, such as the Prairie Queen, can do only so much as long as they're dependent upon muscle power -- but early steam engines are unsuitable for field work. Intensive human labor can actually reduce the quality of diets, until things backslide.

Improvements in draft horse breeding and implement construction result in increases in production. Early draft horses struggled in heavy clay soil, so oxen were still used, but larger draft horses could produce more power to cut through heavy soils with better plows (although John Deere's Prairie Queen remained in the future).

The consequences of energy constraints on muscle-powered irrigation and those on yields, which affects population densities.

An in-depth examination of animal traction, and the biomechanics of why the Bovidae can't produce as much power as equines (he looks primarily at horses, and doesn't really look at draft mules, mostly because draft horses breed and every mule is a one-shot). Why once the horsecollar spread to Europe, oxen were much less important. Then an examination of human-powered pumps: shadufs, corkscrews, bucket waterwheels...

Relative yields and nutrient contents of grains, legumes and meat, and how this affected agricultural practices in traditional societies. The problem that the power units (oxen, water buffalo, horses, etc) have to eat too, and land has to be set aside for fodder crops for them.

The constraints on foraging that make it far less rich than it might appear, and the drivers of the shift to farming. Hoe agriculture vs. plow agriculture, and the evolution of plow technology from simple scratch plows pulled by humans to moldboard and wheeled plows designed to be pulled by hooved animals -- oxen and later horses (after the invention of the horse collar).

Food choices, food preferences and attitudes toward the work necessary to forage preferred vs. non-preferred foods. The taste for fatty animals vs. lean ones, at least partly because fat has more energy (viz polar bears eating the blubber of seals).

Studying foraging behaviors among present-day hunter-gatherers. Tropical rain forests may *look* rich in life, but it turns out that available calories aren't as common as appearances would suggest. Many are out of reach, requiring risky climbs or other techniques that have a high chance of leaving skilled foragers dead or badly injured. Oddly enough, available calories are more abundant in grasslands.

The fundamental problems of comparing the efficiencies of traditional and industrial agriculture. How to treat the inputs of fossil fuels (stored solar energy from ancient life) vs. the food and fodder of people using animal traction for power? The net energy cost of human labor whether using body-powered tools or externally powered tools and the human providing executive function. Natural history of genus Homo.