ATLANTA - As monkeys go, sooty mangabeys aren't cute. Big-fanged, gray and hairy, they simply stare when threatened. Few zoos stock them. Some animal rights advocates can't even spell the species' name. Nevertheless, the sooties are at the center of a precedent-setting debate over whether researchers should be allowed to experiment on an endangered species. Scientists at the Yerkes National Primate Research Center in Atlanta have nurtured a group of these primates for decades. But after Yerkes started the colony, federal officials listed sooties as endangered. The result: Yerkes has the world's largest collection of captive sooties, but with little...