Govind Tekale
Scientists at Colossal Biosciences have created genetically modified “woolly mice” with thick, wavy golden coats as part of their broader effort to bring back the extinct woolly mammoth. This development, announced in March 2025, represents what the company calls a significant step toward their goal of de-extinction.
The experiment involved editing seven genes in laboratory mice, targeting traits such as hair length, texture, and fat metabolism. These modifications were designed to mimic characteristics that helped mammoths survive in cold environments thousands of years ago.
“For us, it’s an incredibly big deal,” said Beth Shapiro, chief science officer at Colossal Biosciences. “This is really validation that what we have in mind for our longer-term de-extinction project is really going to work.”
The Dallas-based company has ambitious plans beyond this initial experiment. Colossal aims to produce mammoth-like Asian elephant embryos by next year and their first calves by 2028. Their de-extinction efforts also extend to other species, including the dodo bird and Tasmanian tiger.
Scientific Process and Results
Colossal’s researchers compared ancient genetic material from mammoths with genetic sequences of African and Asian elephants to identify genes responsible for mammoth-specific traits. They then located similar genes in mice and used CRISPR technology to make genetic modifications.
The experiment produced mixed results. While the mice developed noticeably longer, wavy golden fur, they didn’t appear to weigh more than regular mice despite the company’s claims about increased fat reserves. Additionally, none of the mice have been tested for cold tolerance, according to Nature magazine.
The scientific team implanted genetically modified embryos in female lab mice that gave birth to the first of the woolly pups in October 2024.
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Scientific Reception
The scientific community has expressed both interest and skepticism about the experiment’s significance.
“I’m pretty skeptical about this, but that mouse is pretty adorable,” said Vincent Lynch, a professor of biology at the University at Buffalo. “And for people like me who want to understand the genetic basis of traits, this is particularly impressive.”
Other scientists have been more critical. Evolutionary paleontologist Tori Herridge pointed out that similar mice—called “fancy mice”—have existed since the 1800s, with some varieties already having similar hair characteristics to those engineered by Colossal.
“All the genetic edits Colossal made to their woolly mice were edits already known to produce hairy mice,” Herridge noted in an analysis of the experiment.
Stephan Riesenberg, another expert in the field, questioned the significance of the woolly mice, describing them as a “small, perhaps trivial step towards de-extinction.”
Ethical and Practical Concerns
The broader goal of de-extinction has drawn substantial criticism on multiple fronts.
Karl Flessa, a professor of geosciences at the University of Arizona, expressed concern about potential ecological disruption: “I don’t know what the downside of having a bunch of hairy Asian elephants stomping around in the tundra might be. I don’t know what would happen. They don’t know what would happen.”
Gabriela Mastromonaco, senior director of wildlife science at the Toronto Zoo, argued that the focus on de-extinction diverts resources from more pressing conservation needs. “There’s species disappearing every day,” she said.
Geneticist Adam Rutherford has been particularly critical of mammoth de-extinction efforts, calling it “scientific folly” and a “morally questionable gambit in a time when tens of thousands of species are threatened with extinction.”
Rutherford highlighted numerous practical obstacles, including the fact that mammoths and Asian elephants diverged approximately 6 million years ago—roughly the same time humans separated from chimpanzees. This vast evolutionary distance creates significant challenges beyond simply editing a few genes.
Colossal’s Defense
Colossal maintains that bringing back extinct species could benefit ecosystems where these animals once played important roles. They also argue that the technologies they’re developing could help protect currently living species.
“Current conservation models work. They just don’t work at the speed at which we are changing the planet and eradicating species,” said Ben Lamm, Colossal’s co-founder and CEO. “So we need new tools and technologies so we can engineer life in a better way that’s more adaptable to be co-existent with humans.”
Beyond mammoth de-extinction, the company suggests that their research could help restore Arctic ecosystems and potentially mitigate climate change. Critics, however, remain unconvinced by these claims.
The woolly mouse experiment has sparked widespread media coverage and debate, raising important questions about the direction of conservation efforts, the ethics of genetic engineering, and how we should allocate resources to protect biodiversity in a time of unprecedented species loss.
