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but also for reasons that are of direct benefit to mankind. It is not known which plants and animals may prove useful in the future. It is known, however, that certain animals have proven invaluable to our knowledge of diseases and human health. For example, armadillos (Dasypus novemcinctus) have taught us much about leprosy as they are the only animal model to acquire this disease when injected with Mycobacterium leprae experimentally (Storrs et al., 1980). The small cotton-top tamarins (Saguinus oedipus) from South America have the highest incidence of colon cancer of any animal and have proven to be an excellent species for the study of this fatal disease (Lushbaugh et al., 1984). Studies of spontaneous diabetes mellitus in the South African hamster (Mystromys albicaudatus) (Stuhlman, 1979) and AIDS (acquired immunodeficiency syndrome) in the macaque (Macaca cyclopis, M. mulatta, or both) may eventually lead to cures in humans (Letvin and King, 1984). Hepatitis B virus was discovered in a group of North American woodchucks (Marmota monax) by a zoo pathologist at the Penrose Research Laboratories in Philadelphia (Snyder et al., 1982). The study of the livers of these animals has given human medicine the greatest insight into the etiology of this often seen liver tumor. There are many more examples. Because of the diversity of species, there can be and, in fact, is a broader base of general medical knowledge that is benefiting mankind.
One bright spot in the otherwise gloomy picture of animal extinction is the new interest that has been generated in the field of wildlife reproduction. Fueled by the groundwork laid by the agricultural industry, zoo researchers have begun to study the reproductive processes of wild animals and to use technology such as embryo transfer and artificial insemination to help improve the reproductive potential of wild animals. Zoos worldwide have begun to pursue newfound roles as conservators rather than merely displayers of wildlife.
One of the biggest problems plaguing animals in today’s zoos is the loss of genetic diversity due to inbreeding. This is particularly true with species whose numbers have been so depleted that they cause a genetic bottleneck. For example, the douc langur (Pygathrix nemaeus), a primate from Southeast Asia, is now virtually extinct in the wild, and there are not enough in captivity to ensure the genetic diversity necessary to keep the species alive (Gorman, 1980). With no new blood, so to speak, they can pass only a limited array of genes to their offspring, and as a result, they gradually become genetic carbon copies lacking the built-in adaptability to environmental change that would otherwise occur through natural selection in a genetically diverse group. Genetic diversity is a key to species survival. A species must have enough variation within its genome to enable it to adapt to environmental changes.
Inbreeding has taken its toll in the zoo world, resulting in problems such as decreased fertility, high juvenile mortality (known as inbreeding depression), and birth defects. In 1973, to help fight inbreeding, Ulysses Seal and Dale Mackey created ISIS (the International Species Inventory System), which is based at the Minnesota Zoo (see Chapter 33). ISIS computers catalog animal information from nearly 200 zoological institutions worldwide, including genealogy information for individual animals. One of the best functions of ISIS is that of a computerized