There is now an ongoing, unprecedented loss of species diversity throughout the world as well as a decline in the absolute numbers of organisms from the smallest microorganism to the largest mammal. The current loss of biota has several causes. One is the destruction, conversion, or degradation of entire ecosystems with the consequent loss of entire assemblages of species. Another is the accelerating loss of individual species within communities or ecosystems as a result of habitat disturbance, pollution, and exploitation. Third, and more subtle, is the loss of genetic variability. Selective pressures such as habitat alteration, the presence of chemical toxins, or regional climate changes may eliminate some genetically distinct parts of the...