In agriculture, crop yield (also known as "agricultural output") is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself (e.g. one wheat grain produces a stalk yielding three grain, or 1:3). The figure, 1:3 is considered by agronomists as the minimum required to sustain human life.

One of the three seeds must be set aside for the next planting season, the remaining two either consumed by the grower, or one for human consumption and the other for livestock feed. The higher the surplus, the more livestock can be established and maintained, thereby increasing the physical and economic well-being of the farmer and his family. This, in turn, resulted in better stamina, better over-all health, and better, more efficient work. In addition, the more the surplus the more draft animals -- horse and oxen -- could be supported and harnessed to work, and manure, the soil thereby easing the farmer's burden. Increased crop yields meant few hands were needed on farm, freeing them for industry and commerce. This, in turn, led to the formation and growth of cities.

Formation and growth of cities meant an increased demand for food stuffs by non-farmers, and their willingness to pay for it. This, in turn, led the farmer to (further) innovation, more intensive farming, the demand/creation of new and/or improved farming implements, and a quest for improved seed which improved crop yield. Thus allowing the farmer to raise his income by bringing more food to non-farming (city) markets.