For more than a decade, scientists have chased the idea of reviving extinct species, a process sometimes called de-extinction. Now, a company called Colossal Biosciences appears to have done it, or something close, with the dire wolf, a giant, extinct species made famous by the television series “Game of Thrones.”
In 2021, a separate team of scientists managed to retrieve DNA from the fossils of dire wolves, which went extinct about 13,000 years ago. With the discovery of additional DNA, the Colossal researchers have now edited 20 genes of gray wolves to imbue the animals with key features of dire wolves. They then created embryos from the edited gray-wolf cells, implanted them in surrogate dog mothers and waited for them to give birth.
The result is three healthy wolves — two males that are 6 months old and one female that is 2 months old, named Romulus, Remus and Khaleesi — that have some traits of dire wolves.
They are big, for one thing, and have dense, pale coats not found in gray wolves. Colossal, which was valued at $10 billion in January, is keeping the wolves on a private 2,000-acre facility at an undisclosed location in the northern United States.
Beth Shapiro, the chief scientific officer of Colossal, described the wolf pups as the first successful case of de-extinction. “We’re creating these functional copies of something that used to be alive,” she said in an interview.
The animals will remain in captivity. But the technology that the company has developed could potentially help conserve species that have not yet gone extinct, such as the critically endangered red wolf, which is largely limited to North Carolina.
In 2022, red wolf-coyote hybrids were discovered in Texas and Louisiana. On Monday, Colossal also announced that it had produced four clones from the hybrids. Hypothetically, introducing these clones to North Carolina could improve the genetic diversity of the red wolf population there and help the species avoid extinction.
Over the years, scientists have proposed various ways of reviving a lost species. Suppose, for instance, that they recovered an intact cell from the frozen carcass of a woolly mammoth. Perhaps the cell could be thawed and used to create a mammoth clone.
The entrepreneurs and scientists who started Colossal in 2021 took a different path. They would analyze ancient DNA to identify the key mutations that made extinct species distinct from living relatives. The researchers would then engineer the DNA of a living relative and use those genes to produce viable animals. The revived animals would not be genetically identical to the extinct species, but they would be identical in crucial ways.
Colossal initiated high-profile experiments on woolly mammoths and the dodo, a flightless bird that went extinct three centuries ago. Then the challenges emerged.
For one, while it is relatively easy to make a single edit to the DNA of an animal, the scientists hoped to make dozens of edits. Then there was the matter of producing animals from the edited DNA. The researchers at Colossal envisioned growing mammoth fetuses in Asian elephant surrogate mothers, but no one had ever carried out in vitro fertilization with elephants. To resurrect a dodo, they would somehow have to maneuver a modified bird embryo into a hard-shelled egg.
In 2023, the Colossal team began to focus on dire wolves as a potentially easier target species. Dire wolves are related to dogs, so scientists could take advantage of years of research on cloning dogs and implanting dog embryos.
“We’ve done a lot of work on dogs, because people love everyone’s favorite domesticated gray wolf,” Dr. Shapiro said.
Dr. Shapiro, who joined Colossal in 2024, was part of the team that first retrieved dire-wolf DNA from fossils in 2021. But that work recovered only traces of genetic material. At Colossal, she and her colleagues decided to search for more dire-wolf DNA, hoping to better understand the biology of the extinct species — and perhaps revive the animal.
“It was the simplest path to get a predictable result,” Dr. Shapiro said.
The team took a fresh look at dire-wolf fossils, using new methods for isolating DNA. This time they hit the jackpot, discovering a wealth of genetic material in two fossils — a 13,000-year-old tooth from Ohio and a 72,000-year-old skull from Idaho. The dire-wolf genomes allowed Dr. Shapiro and her colleagues to reconstruct the history of dire wolves in greater detail.
Dire wolves turned out to belong to the same lineage that gave rise to the wolves, jackals and African wild dogs living today. The dire wolf split off from the main branch about 4.5 million years ago. Subsequently, about 2.6 million years ago, dire wolves interbred with other species, including the ancestors of today’s gray wolves and coyotes.
Dire wolves dominated southern Canada and the United States, according to Julie Meachen, a paleontologist at Des Moines University who worked on the ancient DNA project. And they outcompeted gray wolves, being 25 percent bigger and possessing massive teeth and jaws. They hunted horses, bison and possibly mammoths. When many of those prey species became extinct — probably in part because of human hunters — the dire wolf may have been doomed, and the gray wolf swept down from northern Canada and Alaska to fill the ecological void.
Dire wolves and gray wolves are more than 99 percent genetically identical, Dr. Meachen and her colleagues found. Eighty genes were dramatically distinct; some are known to influence the size of living dogs and wolves — suggesting that they were responsible for the big bodies of dire wolves.
More surprising was the discovery that dire wolves carried genes for a light-colored coat, and the hair was probably thick and dense. Dr. Shapiro and her colleagues are preparing a paper describing those results.
Recipe for a Dire Wolf
With a list of dire wolf genes in hand, the scientists at Colossal started their de-extinction project.
First, they isolated cells from the blood of gray wolves and grew them in a dish. There, they tinkered with the wolf DNA.
Ten years ago, scientists altered a single gene in beagles to give them big muscles. Since then, researchers have learned how to edit several genes at once in mammal DNA. For the dire-wolf project, the Colossal team set out to edit 20 genes, pushing the technology to its current limits.
The scientists introduced dire-wolf mutations to 15 genes. But they did not introduce the remaining five, because previous studies had shown that those five mutations cause deafness and blindness in gray wolves.
So the Colossal team found mutations to those five genes that are present in dogs and gray wolves without causing diseases. They introduced those five backup mutations into the gray wolf cells.
“It’s a fine line you have to walk,” Dr. Shapiro said. “You want to be able to resurrect these phenotypes, but you don’t want to do something that’s going to be bad for the animal.”
The researchers then transferred the edited DNA from the gray wolf blood cells into an empty dog egg. They created dozens of these eggs, which they implanted into large dogs that served as surrogate mothers.
Most of the embryos failed to develop, but four pups were born. One died from a ruptured intestine after 10 days, but an autopsy showed that the death was not the result of a harmful mutation.
Matt James, the chief animal officer at Colossal, oversaw the pregnancies and births. He could tell the experiments were a success the moment he spotted the white coat of a pup.
“That first flash of white was a real slap in the face,” Dr. James said. “It’s going to stick in my memory forever.”
Two of the pups, Romulus and Remus, are named for the mythical founders of Rome, who were raised by a wolf. The third pup, Khaleesi, is named for a leading character in “Game of Thrones.”
Dr. James said that the wolves were about 20 percent bigger than gray wolves their age. Not only is their fur white and thick, but they also sport unusually bushy tails and a mane-like growth of hair around their neck.
The researchers are waiting to see just how big the wolves get and have an eye out for any unexpected changes to their biology. “I’m fascinated to see what happens,” Dr. Shapiro said.
She added that the animals were unlikely to reveal much about the behavior of dire wolves, given their captive rearing.
“I would love to know the natural behavior of a dire wolf,” she said. “But they are essentially living the Ritz Carlton lifestyle of a wolf. They can’t get a splinter without us knowing about it.”
Adam Boyko, a geneticist at Cornell University who was not involved in the project, said, “It’s exciting that we can make functional versions of extinct species.” But he did not consider Romulus, Remus and Khaleesi to be truly resurrected dire wolves. They are not being raised in dire-wolf packs, where they could learn dire-wolf behavior, Dr. Boyko noted. And they aren’t eating an ancient diet, so they are not acquiring their ancestors’ unique suite of intestinal microbes.
The animals do carry 20 dire-wolf genes, which might reveal something about the biology of the extinct species. But Dr. Boyko speculated that many other genes also helped set them apart from other wolves. “We don’t know what that number is,” he said. “It could be 20, or it could be 2,000.”
Colossal has been collaborating with a number of Native American communities in the United States. The MHA Nation in North Dakota has expressed interest in the dire-wolf project. “Its presence would remind us of our responsibility as stewards of the Earth,” Mark Fox, MHA Nation tribal chairman, said in a statement released by the company
But if animals with dire-wolf DNA were actually introduced into the wild, they would have to survive in a world that is drastically different from the ice age. The huge animals that dire wolves specialized in hunting are either extinct or surviving in small populations. Any resurrected, free-roaming dire wolves would have to turn to smaller prey — and potentially would have to compete with gray wolves.
For their part, gray wolves and red wolves face threats, including hunting, that no amount of genetic wizardry can address.
Last month, 60 environmental organizations protested a bill introduced in Congress that would remove gray wolves from the endangered species list, a change that could lead to more deaths by hunting, the groups warned.
“If signed into law, the bill would effectively sign death warrants for thousands of wolves across the country,” they wrote.
Dr. Meachen, who was not involved in the creation of the wolf pups, said that she had mixed feelings about the de-extinction effort.
“All the little-kid feelings in me say that I want to see what they look like,” she said. “But I have questions. We have trouble with the wolves we have today.”
