The number of higher plant species is estimated to be between 300,000 and 500,000, only a half of which have been identified.3,4 Of these, about 30,000 are edible and an estimated 700 food species have been cultivated or managed by humans for food.5 Only three - rice, wheat and maize - account for almost 60% of the plant-derived calories consumed by humans.6 A diversified genetic base for these crops is essential for ensuring protection against disaster in the form of a common threat to which the few major varieties are susceptible. Diversity in terms of a wide range of species within sustainable ecosystems is even better insurance.
A diversity of crop and animal species adds to social and economic stability through reducing reliance on a single or few species. Such diversity can also contribute to a more efficient use of natural resources and provide a buffering effect against losses to diseases, pests and weather fluctuations, because species have differing traits which make them more or less susceptible to these variables which affect survival, growth and yield. This differential ability to withstand micro- or macro- environmental stresses is based on the genetic diversity both within and among species. It is genetic diversity which allows species to adapt to changes in ecosystems through natural or human selection.
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