FORGET THE elephant shrew—meet the mammoth mouse. On March 4th Colossal Biosciences, a company trying to revive long-gone species, announced that they had genetically engineered a Mus musculus to have qualities of the extinct Mammuthus primigenius. Instead of Earth-shaking stature or enormous tusks, the creature possessed an abundance of dense, golden fur. It was, in other words, adorable. “That was the main unintended consequence,” says Ben Lamm, Colossal’s boss and co-founder.
Colossal’s long-term goal is on a larger scale. The company wants to create real mammoths, by growing gene-edited embryos of Asian elephants to term. To understand which edits are needed, the firm’s scientists must work out which tweaks give rise to mammoth traits. That is hard to test in elephants, partly because these animals gestate for 22 months—which is a long time to wait for data—and partly because they are endangered, highly intelligent creatures which cannot be experimented upon willy-nilly. To circumvent these difficulties, the company’s scientists set out to test which edits might lead to mammoth-like features in mice instead.
Led by Beth Shapiro, an expert in ancient DNA, Colossal’s team first searched for mouse mutations already known to cause woolly fur. At the same time, they also compared ancient mammoth genomes that had been naturally preserved with genomes from present-day Asian elephants. By doing so, the team was able to pinpoint genes that might contribute to a specifically mammothy appearance, rather than a purely elephantine one. The literature could then be scoured to see if mutated versions of those genes existed in mice.
The team settled on ten mutations in ten genes: nine related to hair and fur and one linked to fat storage, which may have kept mammoths insulated on the tundra. Thus armed, the team at Colossal began to engineer those mutations into laboratory mice using tools based on the gene-editing technology called CRISPR, which can be thought of as a pair of molecular scissors that makes cuts in specific genes.
In experiments conducted on several groups of mice in 2024, combinations of these ten genes were tweaked. The resulting mice were not hybrids—they contained no DNA taken from actual mammoths—but did wind up sporting dense, woollen fur. The mutation put into the fat-storage gene, however, did not immediately lead to heavier mice. Whether this changes with diet and temperature remains to be seen. Indeed, the next step will be to test whether the new physical traits give the woolly mice any advantage in handling the cold. This will be done during the coming year, says Dr Shapiro.
The results are intriguing, but a resurrected mammoth remains far away. Making a mouse woolly is one thing—tweaking an elephant to be woolly, small-eared and cold-resistant is a truly mammoth task. “It’s the first step on a long journey,” says Eske Willerslev, a specialist in ancient DNA at the University of Cambridge, who was not involved with the work.
There are many more unknowns along the way. For one thing, says Patricia Chrzanova Pecnerova, an elephant researcher at the University of Copenhagen, it is unclear if an Asian elephant whose genome had been similarly edited would be a true mammoth or just a long-haired elephant. Different scientists will have different opinions about when de-extinction has been achieved.
Whether it should be attempted at all remains hotly debated. Critics point out that resurrected mammoths might not bond with their elephant mothers, and could have health problems. They also contend that money invested in such endeavours would be better spent protecting existing species. Mr Lamm and Dr Shapiro, for their part, say they raise money for conservation, and point out that all the technology their company develops has been made freely available to conservationists. With many species struggling to adapt to climate change, they argue, the gene-editing tools used to reverse extinction might also help prevent it. ■
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