Reviving Ghosts: The Return of the Dire Wolf and the Promise of De-Extinction
Romulus and Remus, two lively pups, exemplify typical puppy behavior: chasing, wrestling, and exploring. Yet, at just six months old, their size is anything but ordinary. Measuring nearly four feet in length and weighing around 80 pounds, they could soon grow to six feet and 150 pounds. Their demeanor is distinctively un-puppy-like; they shy away from human contact, contrary to the cuddly nature of most puppies. This reserved behavior is characteristic of wild wolves, not domestic dogs—these are dire wolves, long thought extinct.
Once widespread across the Americas, from Venezuela to Canada, the dire wolf disappeared over 10,000 years ago. However, discoveries of their remains across the continent have provided a unique opportunity for Colossal Biosciences, a company dedicated to de-extinction. Using sophisticated genetic engineering and preserved ancient DNA, scientists at Colossal successfully reconstructed the dire wolf genome. They modified the genetic code of the common gray wolf and, with the help of domestic dogs as surrogates, brought Romulus, Remus, and their younger sibling, Khaleesi, to life. TIME was granted a visit to the wolves’ secluded home at a U.S. wildlife facility on March 24, with strict conditions to protect these remarkable creatures from public curiosity.
Colossal, founded in 2021 with a team of 130 scientists, aims to resurrect a host of extinct species. Beyond dire wolves, they plan to revive the woolly mammoth, the dodo, and the thylacine. Already in March, they stunned the scientific community by creating a “woolly mouse,” a tiny creature possessing the mammoth’s distinctive long fur and rapid fat metabolism.
Some skeptics liken Colossal’s endeavors to a P.T. Barnum spectacle, but the company defends their work as vital for conservation. By refining the techniques used to restore extinct species, they hope to bolster endangered ones. Through recreating the mammoth, they suggest, we can create resilient elephants better suited to withstand climate change. Reviving the thylacine may benefit related species like the quoll, while lessons learned from the dire wolf could aid in saving the red wolf from extinction.
“Humanity has become a pivotal evolutionary force,” asserts Beth Shapiro, Colossal’s chief science officer. With predictions that 30% of the world’s genetic diversity may vanish by 2050, she argues that genetic engineering is crucial to reversing this loss. Ben Lamm, Colossal’s CEO, views the technology as a moral obligation—an opportunity for humans to amend the harm we’ve caused to Earth’s biodiversity. “If we want a future rich in both diversity and human presence,” Shapiro emphasizes, “we must harness our intelligence to mend the damage we’ve inflicted.”
Although the woolly mouse suggests promising potential, the introduction of dire wolves has profound implications. Not all scientists agree with this ambitious project, citing historical instances of introduced species proliferating unchecked and disrupting local ecosystems. Unanticipated consequences have emerged before—exotic pets wreaking havoc on native fauna or introduced predators harming the animals meant to be conserved. Genetic engineering remains a burgeoning field, and cloning comes with risks such as large offspring syndrome and other health complications in cloned animals. The process also poses challenges, including the strain on surrogate mothers.
“There are significant risks,” warns Robert Klitzman, a bioethics professor at Columbia University. “These include potential fatalities and severe complications, leading to considerable suffering and possible miscarriages.”
Nevertheless, Colossal’s team is enthusiastic about their progress. Matt James, chief animal officer at Colossal, recalls a poignant moment when Romulus and Remus were just five or six weeks old. During a routine checkup, as a veterinary technician sang a song from The Little Mermaid, the pups responded with a long-lost howl—an eerie sound not heard for millennia.
“I was stunned,” James recounts. “That howl marked the return of a voice long thought silenced.”
Only minor genetic modifications separate living species from their extinct relatives. Wolves, like other canids, possess about 19,000 genes. To recreate the dire wolf, Colossal made just 20 edits in 14 genes of the gray wolf. These changes produced significant differences, such as the wolves’ distinctive white fur, robust build, and unique vocalizations.
To identify necessary genetic changes, researchers analyzed the dire wolf genome from two ancient samples: a 13,000-year-old tooth from Ohio and a 72,000-year-old ear bone from Idaho, provided by museums. The subsequent laboratory work was meticulous.
Unlike traditional cloning, which requires a donor tissue sample, Colossal utilized blood-derived endothelial progenitor cells from a gray wolf. They precisely edited these cells’ nuclei to align with dire wolf genes—no actual ancient DNA was integrated. This modified nucleus was then transferred into an ovum stripped of its own nucleus. Of 45 engineered ova, laboratory-grown embryos were implanted in two surrogate hounds, chosen for their health and adequate size. Both surrogates successfully carried one embryo to term, resulting in the births of Romulus and Remus on October 1, 2024, and Khaleesi following suit in January 2025.