Cloning is in the news again, as it has been regularly since the birth of Dolly the cloned sheep in Scotland in 1996. The last four years have seen a flurry of Dollies -- more sheep, cattle, pigs and mice -- and numerous bulletins on their progress, which has mostly proved surprisingly normal. In the beginning, each new case was accompanied by competing drum-rolls of apocalyptic commentary: Cloning, we were told, put humanity on the threshold of either a brave new world or a door into the dark.

Over time, the hubbub died down a bit. But it has been revived by the latest announcement, with opinion dividing along the usual lines. Sometime in November, a surprised American cow named Bessie is due to give birth, not to a naturally conceived baby cow, but to a cloned baby Asian gaur -- a hulking, humpbacked, blue-eyed wild ox. In the animal's native India and Southeast Asia, gaur numbers are dwindling fast. This fetus, cloned from a single cell, thus represents an important double advance: It is the first time an endangered species has been cloned and the first time a cloned animal has been gestated in the womb of another species. (Gaur are evidently too precious to use in experiments.) The technology is not new on either count -- animal cloning as such is now routine, and scientists had already brought off cross-species surrogate births. It is the imaginative combination of existing technologies in Bessie's case that has reignited the debate and given it a new twist.

What are the hopes? On the broadest scale, scientists see this as a way of saving endangered species and even recovering recently extinct ones. That's why the unborn gaur has been named Noah (rather than, say, Al, after the conservation-minded U.S. vice president): "He will be the first endangered animal we send up the ramp of the ark," says Mr. Robert Lanza of Advanced Cell Technology, the Massachusetts company behind this and similar upcoming projects. Plans are also under way to clone giant pandas and a species of Spanish goat that died out earlier this year. With up to 100 species disappearing daily, proponents see cloning as the only alternative to mass extinction.