A basic concept of sustainable agriculture includes using resources in a way that does not deplete or permanently damage systems used for plant and animal production. In early history, humans survived as hunter–gatherers and perhaps less than 1% of biomass could be used as food (Diamond, 1997). As a result, most resources in the environment were not likely to be used directly by humans. The limited availability of food also restricted population growth, helping to make the hunter–gatherer way of life sustainable. In contrast, domestication of crops and animals for food has greatly increased edible biomass, leading to dramatic population growth and the possibility that production of adequate food will lead to longterm damage to agricultural systems.