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.

What are the concerns? Surprisingly, the strongest objections have come from wildlife conservationists. Lack of genetic diversity is one worry. But an even bigger one, to some, is the impact of such a high-tech approach on conservation’s traditional goal: restoring and preserving the natural habitats whose loss is the main cause of the death of species. “That animal,” said one distraught scientist from the Wildlife Conservation Society in New York last week, “will never live its life in true gaurdom, to wander in the forests of India and frolic with other gaurs.” Opponents of cloning argue that it will only let developers off the hook, thereby hastening the destruction of natural environments.

From here, of course, it is impossible to see whether cloning will prove a godsend or a disaster or something in between in the effort to stem the flood tide of extinctions. But one thing is clear. No matter how fierce the debate — or how right the doom-and-gloom party turns out to be on any particular aspect — nothing will stop researchers pushing ahead with cloning, gene therapy, gene transfers and all the rest of it, to the limits of the imaginable and beyond. After a certain point, scientists proceed not because they should, but because they can. “The important thing in any science,” said the physicist Edward Teller, a father of the atomic and hydrogen bombs, “is to do the things that can be done.” Although this was said in the context of the 1950s debate over the ethics of developing the hydrogen bomb, it was also a flat statement of fact. Science has a momentum and, it is implied, an ethic of its own.

The truth of this was underlined by a separate development last month: the announcement by a radical Canadian religious group that it is poised to carry out the first cloning of a human being. A U.S. couple has reportedly contracted to have cells from their infant daughter, who died accidentally, cloned and implanted in 50 volunteer surrogate mothers. Despite the lunatic-fringe quality of the venture — the group believes that humans are clones of extraterrestrials to begin with and has no scientific or medical standing — mainstream researchers acknowledge that a successful human cloning is technically possible right now. “I have no doubt,” said a Princeton biologist, “it will happen very soon.”

When it does (not if), it will make Bessie’s strange offspring seem as ordinary as test-tube babies and paper-cutout sheep do today. That is comforting, in a way. But so is the grumbling of the naysayers, whose reflexive doubts about innovation put such a healthy brake on science. Some roads do lead to apocalypse — as Teller must have known.

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