The domestication and breeding of animals represented a major energy transition for humans who previously represented the sole biological converter of food into calories. The energy of human labor made the major capital investment profitable. Through exhausting and dangerous labor, men using shovels, hammers, and drills dredged the bottoms of major rivers. Coal-powered steam engines were used to drain water from mines, work done previously by human- and horse-powered windlasses, a wooden device to lift coal from a shallow mine. Energy transitions may result in abandoning one power source and replacing it with another. A more common practice is a layered one in which a new energy source is added to the mix and over time becomes dominant by releasing more energy to do work. By 1880 CE, wood, thatch, straw and other biomass gave way to coal as the world’s main commercial energy source.