For the first time, scientists have cloned an endangered U.S. species: a black-footed ferret named Elizabeth Ann, whose donor has been dead for more than 30 years. After the original ferret, Willa, died in 1988, scientists froze her body to preserve her genetic material, hoping to someday perform an experiment like this. While a domesticated ferret carried the cloned embryo, the new ferret, who is being raised at a Fish and Wildlife Service black-footed ferret breeding facility in Fort Collins, Colorado, is still very wild, with all the instincts and aggression that suggests. This is a fresh success story for the black-footed ferret, which has become emblematic of how well conservation and repopulation efforts can work. First, scientists thought the ferret was extinct, after frustrated ranchers poisoned almost all of the animals in the wild. Then, the population grew from a group of just a few, so there are about 1,000 wild black ferrets today—plus populations in wildlife...