Only three northern whites are left—and the Frozen Zoo is the only way there’ll ever be any more. San Diego Zoo Global © 2016

Only three remain. Three. The fourth, Nola, used to live here, right next door to the Frozen Zoo, in the San Diego Zoo Safari Park. She died last November, at the advanced age of 41. Four or five decades is about as long as any white rhino lives. The trio are kept in a wildlife preserve in Kenya called Ol Pejeta: Najin, Fatu, and the last male northern white rhino on the face of this Earth, Sudan. The three have failed to reproduce. (They are also, it should be said, related: Najin is Sudan's daughter, Fatu his granddaughter. Incest is their best defense against extinction. Make of that what you will.) Sudan is 43; his sperm count is perilously low. In 2015, doctors determined that neither of the two females was capable of breeding. Maybe the concrete floor of the zoo where they lived before coming to Ol Pejeta wrecked their hips.

Dr. Barbara Durrant, San Diego Zoo Global's director of reproductive physiology, who also works on the Frozen Zoo with Ryder, is attempting an in vitro workaround—northern white sperm and northern white ovarian tissue harvested from the live northern whites, combined into a fertilized embryo, and then re-implanted back into one of the two females. They're practicing on southern whites now. But there is still much that is mysterious about the reproductive cycles of rhinos. “No embryo transfer has ever been attempted in any rhino species,” says Durrant. And time is running out.

They are ghosts. Even now they're disappearing into what's known as the extinction vortex: “the notion,” Ryder explains, “that we have that a population can be doomed but there's still numbers of them around. The numbers get smaller and it becomes a feedback loop. Like water going down a drain: It's deterministic. Or a mass entering a black hole. Once you hit the event horizon, you're out of here.”

The northern whites are out of here.

III. How to Bring Them Back

Let's say in vitro fails. Let's say northern whites have hit the event horizon. This is where the Frozen Zoo really comes in. It begins with cells. You gotta collect them. So, first clean the site: Shave one tiny part of the animal, ideally while it's alive and anesthetized. Next, as Ryder explains, “take sterile tweezers and a sterile scalpel and you take a little piece. It doesn't have to be any bigger than a grain of rice. Then you take that material and you make a cell suspension out of it”—meaning, basically, that you put those cells in flasks, in a broth that's designed to encourage them to multiply. You fill up a flask. And then you divide the suspension in half and put it into two flasks. “One becomes two, two becomes four,” Ryder says. Soon, “we've got enough to freeze eight vials.”

The multiplied cells in the vials are called fibroblasts—the common, connective tissue that makes up all animals, including us. Now, reprogram those cells into what are known as induced pluripotent stem cells. “That means you have taken that cell and kind of turned back time to when it was a stem cell,” Durrant says. “So it can't make everything in the body, but it can make all three of the germ layers that you would see in an early embryo. It can make any of those.”

One of those germ layers is what eventually becomes sperm or eggs. “It's very complicated, every step of the way, and there are many steps,” Durrant says gently, reading the look of total incomprehension on my face. But the gist is: Collect the cell, turn it back into a stem cell, tell that stem cell how and what to become anew. Namely: sperm and eggs.

Finally, the easy part of this whole terribly difficult exercise in playing God: You take those sperm and eggs, combine them, then fertilize and implant the egg into a surrogate—something close to the original, such as a southern white. The southern white gives birth to a northern white. From cells, life. From life, more life. The rhinos wink out. They wink back on.

IV. Life and Death in the Extinction Vortex

The frozen zoo is both a monument to and a counterforce against the extinction vortex. The zoo and its staff are poised at the edge of existence, that shadowy plane where things are sort of alive and sort of dead, where the arrow could point both ways. All the doctors at the zoo have stories about what it's like to labor in this sad zone. What it was like to be there when Nola died, for instance. The northern whites are of particular interest to the Frozen Zoo's researchers. Durrant routinely works with species right on the brink. She is freckled, kind-faced, forthright. “There was a lot of grief” when Nola died, she says.

Her other passion is the Yangtze River giant softshell turtle. Rafetus swinhoei. Only two are known to remain, both at the Suzhou Zoo, both over 100 years old. Durrant is working on getting them to reproduce. “There was an additional male in Vietnam—he just died in the last few months. Unfortunately, no one was allowed to collect sperm from him, so nothing was saved. There was a lot of superstition. As long as that animal was alive, then everything was good in the country. When it died, politically and socially and spiritually things changed. No one there was allowed to actually cut into that animal. No one outside was allowed to do it, and they were not willing to do it themselves because there was a lot of superstition about that. One veterinarian had done something with one of those animals in the past, and within 24 hours he was in a motorcycle accident and lost his hand.”

The turtle lived in a lake. “He was alone, he was revered. He was sacred. It was just out of the question that we would do anything with him. No one was allowed to touch him. Even in death we were not allowed to touch him.”

Durrant knows not everyone shares her love for our animal brethren. “I think people talk about it abstractly, but they're not connected to those animals. They don't feel it the way we do.” But their decline, she says, is “a sign of what's happening. It's going to happen more and more and more.” Species dwindling from 1,000 to 500 to 100 to 10 to 5, circling the beveled edge of the extinction vortex like the northern whites already are. Take a slightly longer view and we might all be poised there. Right on the edge.

I wanted to see what that in-between state looked like: here but already gone. And I wanted to understand the incredible—and incredibly expensive, and debatably worthwhile—human effort to save the rhinos and their endangered peers. Ryder and Durrant's work is controversial. “The Frozen Zoo is basically re-arranging the deck chairs on the Titanic,” the eminent Stanford scientist Paul Ehrlich told The Washington Post last year. Ehrlich's argument—and he is far from alone—is that this is all a waste: all that money and energy and time, to maybe save a handful of animals. Why not redirect those resources to lobbying Congress, or preserving rapidly shrinking habitats?

“I don't see Sudan enjoying life anymore,” James says. “The fact that he's the only one, it's not a lovely life. Knowing you're the last male standing—it's really sad.”

There's a psychological undercurrent to the skepticism, too: If you tell lazy humans that we can just bring these animals back, will anybody work to save them in the first place? No. We'll eat them at twice the rate, grind their bodies into jet fuel so that we might run up a few more frequent-flier miles, and count on science to save us when they're gone. Science is like: Nah, fuck that.