In central Kenya, three of the world’s four remaining Northern white rhinos are stubbornly refusing to mate. Since 2009, conservationists have tried and failed to coax the animals together—and with the lone male nearing his 43rd birthday, too old to breed, extinction is inevitable. It’s a matter of time before the remaining beasts die off, one by one.

So in the meantime, in San Diego, scientists are working to resurrect them.

At the Scripps Research Institute, regenerative medicine researcher Jeanne Loring has figured out how to make induced pluripotent stem cells, capable of transforming into any cell type in the body, out of rhino skin. She and her team are now working out how to turn them into rhino eggs and sperm. If successful, they should be able to create new rhinos via in vitro fertilization, saving the animal from extinction—or more likely, bringing it back from the dead.

The white rhino isn’t the only beast on the verge of resurrection. For species that are already wholly extinct, scientists are turning to massive caches of animal and plant cells stored in deep-freeze repositories like the Cryo Collection, buried in the bowels of the American Museum of Natural History. Others are using a method called anthropogenic hybridization—crossbreeding a dying species with a similar, living one so that some of its characteristics survive.

With these methods and others, biologists may soon be able to bring animals back from the dead. That's a thrilling but distinctly unnatural approach to preserving nature. And some scientists and conservationists are asking if resurrection is really the right way to save the Earth's threatened species.

Wild Without the Wilderness

Many of the arguments against resurrection are the same that conservation scientists have heard against their more traditional methods for decades. When the costs are so high—tens of millions of dollars to save a few Kihansi spray toads, for example—it's easy to argue that natural selection is a force humans just shouldn’t mess with. If an animal can’t hack it in a changing world, them’s the breaks. Some scientists, the "hardcore Darwinians," believe that logic applies even when humans are the ones forcing animals like the white rhino and the Pinta tortoise out. “Humans themselves are part of nature,” or so the logic goes, says Joanna Radin, a science historian at Yale. “So it’s survival of the fittest.”

If scientists do choose to save a species, that doesn’t mean it will thrive. When conservationists released the once-endangered whooping crane back into the wild, for example, the birds weren’t able to migrate without following the lead of a human pilot in an aircraft. And if Loring successfully birthed a Northern white rhino, she couldn’t release it into the wild—poachers would kill it. “Until we make space for other species on Earth, it won’t matter how many animals we resurrect,” writes M.R. O’Connor in her book Resurrection Science. “There won’t be many places left for them to exist.”

The places they will be able to exist? Zoos. Loring calls her work “Jurassic Park without the scary parts,” in part because her newly-birthed science experiments might only ever get to roam in a living museum. Some question whether preserving wildlife is valuable if it can't live in the wild. “A tiger in a zoo isn’t really a tiger anymore because it’s not doing its thing,” the environmental ethicist Holmes Rolston III told O’Connor.

An animal robbed of its natural home is hardly an ideal solution, Loring recognizes. “I don’t want to rescue an animal that’s going to exist only in a zoo," she says. "But it’s probably better than not having it at all.”

That fear of missing out is what’s driven scientists to fill freezers with cells from threatened animals—a proto-zoo of a sort. (One facility in San Diego actually calls itself the Frozen Zoo). These DNA banks serve as storage lockers for things that scientists don’t really know what to do with yet: samples from the vulnerable Himalayan clouded leopard and coral from the Great Barrier Reef. “In a way, freezing animals is a concession that we’re not sure how else to save them,” writes O’Connor. Scientists filling the frozen cell banks of the world are attempting a sort of “planned hindsight,” says Radin.

Just what happens to those stores when the animals die out is up for debate. If, as Loring is attempting with the white rhino, induced stem cells could turn into sperm and eggs, scientists could create a new animal in the lab. Or they could attempt to insert certain DNA from extinct animals back into living ones that share some of the same characteristics (one scientist is hoping to co-opt elephant cells this way in an attempt to resurrect the woolly mammoth).

But by focusing single-mindedly on saving DNA—banking on future technological resurrections—scientists may in fact be letting animals' true auras die out. “No one would say that freezing the DNA of humans preserves what makes us human,” O’Connor points out.

To resurrect the extinct Galapagos Pinta tortoise, for example, scientists are inbreeding tortoises that each share a bit of the Pinta’s DNA in the hope that a century from now, one of the offspring might be born with all the DNA of the Pinta. It's arguable, though, whether that jigsaw puzzle of an organism would be the same as the tortoise that once was. "Paradoxically," says O'Connor, "the more we intervene to save species, the less wild they often become.”

Hunter's Remorse

Still, perhaps humans are morally obligated to take care of the species they’ve actively pushed out. To Loring, the white rhino is a good candidate for resurrection both because of its place in our imagination as one of the “great beasts” of Africa, and because of the culprit behind its demise: “The rhino is forced into extinction by a very direct process—people killing them for their horns,” says Loring. “I think we have a responsibility to save animals that we are responsible for killing in the wild.”

But the attempt to save the white rhino might have another driver: human self-interest. Fifty years ago, scientists successfully cloned carp, currently a vulnerable species. But using that technology to increase the fish's numbers isn't nearly as attractive as the redemption story of bringing back the white rhino from the brink of extinction. It’s estimated that human activity is causing Earth’s species to go extinct at 100 times their natural rate. But only those species that have earned favor among humans—or make us feel especially guilty—get a lifeline. “I’m not saving mosquitos," says Loring. "Trust me.”

De-extinction, then, is a uniquely self-gratifying brand of conservation. Resurrection reflects an urge to do something, O’Connor says, “before humanity relinquishes the existence of wild places and wild things in the world.” But it’s for humans, not for the animals. “It really doesn’t matter to a dead species whether they’re brought back,” she says. Perhaps, nostalgia for the great beasts of the world has clouded humans from realizing that what is truly natural may be to let them die out.