specialized invertebrates makes it logistically impossible for technology to contribute to the preservation of a significant representation for restoration programs.

There are only about 41,000 vertebrates. Of these, 19,000 or so are fishes, about 9,000 are birds, 6,000 are reptiles, 3,100 are amphibians, and 4,300 are mammals (E.O.Wilson, personal communication, 1987). For those that have been or will be totally displaced from nature, we have only a few specialized propagation centers and the world’s zoos.

Zoos currently house about 540,000 mammals, birds, reptiles, and amphibians—an almost trivial number in relation to original wild populations but significant in the impact on human interest. The number is roughly equal to 1% of the domestic cats in American households, 10% of the cats and dogs euthanized annually in the United States, or about 25% of the deer taken by U.S. sportsmen each year. Zoos are popular but have little room. The spaces for animals in the world’s zoos could all fit comfortably within the District of Columbia. Even if half these spaces were suitable for propagation of vanishing animals, the individual numbers of each species necessary to keep viable populations would make it impractical for zoos to sustain more than 900 species very long and probably far fewer in conventional breeding programs (Conway, 1986). But it will not always be necessary to sustain a population for a long time or to do so conventionally. Zoos, revised and improved, can come to have a special role in species preservation, for they represent a unique devotion of local human resources to the care of foreign wildlife.

In the past few years, the world’s zoos have bred more than 19% of all the living mammals and more than 9% of the birds. Thus far, criteria of genetic uniqueness as well as the practicality of care have guided long-term propagation programs. In the future, more attention must be given to ecological criteria with an eye toward the future needs of restoration programs, to species that naturally occur at low density, to the great predators and large ungulates, and to the primates. A foundation for such help rests in growing international collaboration and, in the United States, in unequalled programs of coordinated animal data gathering in the International Species Inventory System and species management in the Species Survival Plan of the American Association of Zoological Parks and Aquariums.

Zoos are breeding orangutans and Chinese alligators, Bali mynas, pink pigeons, and Puerto Rican horned frogs, addax, slender-horned gazelles, wattled cranes, and black lemurs. They have pioneered rare embryo transfers between animal species, artificial rearing techniques, cross-fostering between species, and necessary long-term contraceptives for population management—a host of fundamental technological tools essential to the prospects of helping species in extremis.

Even so, extensive scientific and technological advances would be necessary to appreciably expand the space available for the care of species losing their homes. But where cold storage of sperm and embryos is possible, a herd of wild cattle or antelope can be cared for in a space no larger than a soda straw, moved without risk of trauma, and stored indefinitely—if we are satisfied to have our wild cattle and antelopes in soda straws. Yet, we must consider the alternatives and their time scales.

Unfortunately, practically all that we know of animal reproductive physiology has been worked out with a few domestic and laboratory species. The technology

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