> an era where fire exists The labor-cost of energy (food, wood-burning, gasoline, electrical) is a pretty huge factor in human endeavor. Cooking on a hot-spr

> an era where fire exists The labor-cost of energy (food, wood-burning, gasoline, electrical) is a pretty huge factor in human endeavor. Cooking on a hot-spring is thrifty. Local wood runs out quickly when you have lots of people.