When Kurt Benirschke launched a program at the San Diego Zoo in 1975 to freeze cells from endangered species, he assumed that his colleagues would use the collection to unravel complex issues such as the genetic similarities among animals. Never did he imagine that scientists might one day pluck cells from the "frozen zoo" to grow new animals from scratch. But since February, when researchers in Scotland reported they had cloned a lamb named Dolly from the cells of an adult sheep, the notion of cloning a Przewalski's horse, Sumatran rhinoceros, or one of the other rare species whose cells are banked at the San Diego Zoo's Center for Reproduction of Endangered Species (CRES) has suddenly left the realm of science fiction.
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