ABSTRACT
Over the course of the past century, the commercialization of agriculture and technical change encouraged individual farmers and regions to specialize in the production of fewer crops and varieties according to relative physical endowments and trade advantages. One consequence of these changes is that much of the world’s population of over six billion now depends for food on a several hundred modern varieties of a handful of cereal crops. A shared vulnerability to changing pests, diseases and climatic factors might be expected to have led to major food shortages on a global scale.
