Blake Russell was still asleep when he got an alert on his phone. His mare was giving birth. He sprang out of bed and headed to the barn, about 50 yards from his house in Gainesville, Texas.

Russell is used to getting woken up for a late-night delivery. But this foal was special. It was a clone of a rare Przewalski’s horse, a now-endangered species that once roamed the grasslands of central Asia. Crouched in the corner of the barn stall, Russell waited for its birth with anticipation. “When I saw toes and nose, I thought, ‘Whew, this is going as planned,’” he recalls.

You might be surprised that cloned animals exist—they do, but the procedure is mostly used for domesticated animals. Russell’s company, ViaGen Pets, clones around 100 horses a year, as well as cats and dogs.

Yet the technology has rarely been used for endangered animals. Up until that moment, cloning had only successfully produced a single animal of any such species. The new Przewalski’s horse, born in February and still unnamed, is the second of his kind. He’s a genetic copy of the world's first cloned Przewalski’s horse, Kurt, who was born in August 2020. Both were made from cells frozen more than 40 years ago at the San Diego Zoo. The scientists behind the effort say this second birth is evidence that cloning could be a viable strategy for saving endangered species.

“It’s certainly a milestone in conservation,” says Oliver Ryder, director of conservation genetics at the San Diego Zoo Wildlife Alliance, which worked with ViaGen and the nonprofit Revive & Restore to clone the foal. “It offers a new chance for reducing extinction risk and preserving the genetic diversity of species.”

Sandy-colored and with large heads, Przewalski’s horses are shorter and stockier than their domesticated relatives. After centuries of hunting and habitat disruption, the horses became extinct in the wild in the 1960s. Luckily, many were still living in zoos. Starting in the 1990s, captive-born Przewalski’s horses were reintroduced into the wild to establish herds in Mongolia, China, and Kazakhstan. Today, there are about 1,900 left. Nearly all of them are descended from just 12 animals captured from native habitats between 1910 and 1960.

As a species’ numbers dwindle, so does its genetic diversity—the range of inherited characteristics within its population. Generally, the more diverse the gene pool, the longer animals live and the more offspring they have, boosting their chances of survival. But once their population has dramatically shrunk, even if the species rebounds, genetic variation does not. “About half of the gene pool of the wild horses had been lost,” Ryder says. So scientists took matters into their own hands.

The idea of breeding livestock for desirable traits is nothing new—and for the past few decades, some ranchers have turned to cloning their most prized cattle, pigs, and sheep. The team chose the Przewalski’s horse partly because of ViaGen’s experience with cloning domestic horses, and partly because they already know a lot about how horses reproduce and how to care for foals. And perhaps most importantly, the San Diego Zoo already had stored cells from a Przewalski’s horse that was genetically different from the horses living today. Introducing that DNA into the current population could help restore lost genetic variation. “We were looking for a species that had gone through a bottleneck and could use a boost,” says Ben Novak, lead scientist at Revive & Restore.