Symbiosis, Instability, and the Origins and Spread of Agriculture: A New Model [and Comments and Reply]

Section 1 presents evidence that domestication and agriculture are evolutionary phenomena. They may be found in the relationships of many animals with plants. Domestication is the result of coevolved mutualisms between animals and plants. All domesticated plants show characteristics that are evidence of this mutualist relationship. Section 2 is a brief presentation of a model for the origin and spread of agriculture. Agricultural techniques transcend the environmental limitations placed upon the continued development of the human-plant mutualism. First highly mutualistic societies and then agricultural societies, because of greater potential cultural fecundity, come to dominate any given geographical area. This higher potential fecundity is based upon increases in the carrying capacity brought about by the domesticated plant. Agriculture also introduces new instabilities into the productivity of domesticated plants. Recurrent periods of stress, the result of agricultural techniques and plants, bring about the spread of agricultural societies by forcing a subset of the population to emigrate. Agricultural practices maximizing instability in productivity will have the highest rates of dispersal. Thus a positive selection for instability in productivity has characterized agricultural systems from their very origin.