Scientists are working to unlock the secrets to bringing back extinct animals. One potentially important new advance is the creation of genetically altered mice with long, golden locks of tufted fur. They were, in fact, inspired by the coats of woolly mammoths.

The new rodents are being called Colossal woolly mice. And yes, they’re super cute.

As transgenic mice, their genes have been tweaked by engineering. That in itself is not all that special. What’s notable here is that eight spots have been edited across seven genes.

The team did three experiments. Each used a different mix of edits. In all, they created 32 woolly mice. Each varied slightly in appearance.  

All, however, carried the hoped-for traits, notes Beth Shapiro. An evolutionary biologist, she works at the University of California, Santa Cruz. She’s also chief science officer at Colossal Biosciences in Dallas, Texas. There, she was part of a team working on the new mice.

Their gene editing worked well, Shapiro says. They got seemingly healthy animals with some mammoth-like traits. There also were no surprises, she says — “other than that they were so absurdly adorable.”

Her team described its achievement in a paper that posted March 4 at bioRxiv.org.

So what can we expect when it comes to bringing back extinct species? Colossal Biosciences’ founder, Ben Lamm, has said he wants woolly mammoth calves on the ground by 2028.

Can they achieve that?

They’ll start by tweaking Asian elephant genes to be more mammoth-like. Later, they’ll need to put mammoth-like embryos into another animal — likely an elephant — to serve as each calf’s mom.

“We will have elephant cells that are edited and ready to go in early ’27,” Shapiro says. That’s “what we would need to have [calves] on the ground in 2028.” However, she adds, “There’s a lot of hard biology that still hasn’t been solved.” And before those calves are actually born, “that needs to be solved.”

So what is a woolly mouse, exactly?

To create the woolly mouse, scientists analyzed all the genetic instructions — or genomes — in 121 tissue samples from mammoths and elephants. The goal here was to find the genes that might have given woolly mammoths some of their key traits. Those include long, thick, golden hair. They also include genes for absorbing and using fat — important features for animals that lived in the bitter cold.

“We can do a lot with the mammoth genomes we have,” says Shapiro. “We can line them up on a computer and compare them to elephant genomes.”

In this way, her team compared “where all the [mammoths’ genes] are the same as each other but different from their elephant cousins.”

Those differences pointed to what should make a mammoth a mammoth.

The researchers then searched for similar traits in mice. Those could be in naturally occurring genes — or in ones that might be added through genetic engineering.

Mice are much easier to work with than elephants. The tiny rodents require little space. They also breed quickly. And being extensively studied, their genes are already well understood.

For instance, scientists have known since 1994 that mice will grow much longer hair than usual if you turn off a gene known as FGF5. Similarly, a gene known as Mc1r makes mice blond. And the gene Frzd6 makes that hair whorly and frizzled.

The final step in creating the new woolly mice: editing embryos’ genes to help them become living, breathing, gloriously furred mice.

They’re still a long way from mammoths

This gene-tweaking worked with high efficiency. In other words, the scientists not only made woolly mice, but could do so reliably and repeatedly. And that’s actually a big deal, says Shapiro.

“Of course, mice are not elephants,” she acknowledges. Indeed, it’s something critics have often “pointed out to us,” she adds.

And that’s why, she says, these woolly mice are just one part of her team’s de-extinction goal. Colossal Biosciences, started in 2021, has also been experimenting directly with Asian elephant cells. The reason: That species is related most closely to extinct woolly mammoths.

Another arm of the company’s research focuses on techniques to improve artificial reproduction. These are skills that will be needed to implant a genetically modified elephant embryo into a living elephant — one that would ultimately give birth to a “mammoth” calf.

In related work, this team also is working on efforts to bring back the extinct dodo and the thylacine. That last animal, also known as the Tasmanian wolf, was actually a wolflike marsupial.

We can’t just clone woolly mammoths

Jacquelyn Gill is an ice-age ecologist. She works at the University of Maine in Orono. Gill doesn’t hide her excitement about the idea of one day seeing a real live woolly mammoth.

“I understand why someone would be compelled to see a mammoth,” she says. In much the same way, she explains, “I’ve never seen [the ice age] in person, right? It only exists in my mind’s eye, because I study a past that is gone.”

She does not reject the idea of trying to bring back extinct species. In fact, Gill says, “the science of de-extinction is exciting and has broad applications.”

She is skeptical, however, that what Colossal Biosciences is working on will qualify as bringing a woolly mammoth back from the dead.

For starters, many well-preserved mammoth remains have been discovered in permafrost. In some cases, they were complete carcasses with fur, muscles and skin. However, they also had been buried in ice for thousands of years. And that likely destroyed every cell in those remains.

“A mammoth is not an elephant in a fur coat.”

Tori Herridge, evolutionary biologist

Without intact cells, researchers won’t be able to clone a mammoth as easily as some in the past had cloned sheep. “That’s a whole pathway to cloning that is cut off from us,” Gill says.

Gene editing may allow researchers to alter an Asian elephant in ways that make it resemble a woolly mammoth. But any effort to do so will likely miss untold genetic traits that made woolly mammoths unique as a species.

Keep in mind, emphasizes Tori Herridge, “A mammoth is not an elephant in a fur coat.” An evolutionary biologist, she works at the University of Sheffield in England.

Mammoth doubts abound

Herridge does find the idea of identifying candidate genes for mammoth fur and for cold adaptation “really exciting and interesting.” Still, she cautions, we don’t know “what makes a mammoth a mammoth.”

“We all know that genes are complicated,” she says. “One gene can affect many things.” And many genes can act together. What’s more, she points out, researchers don’t yet know if the genes for hair length, texture or color in the woolly mice will produce the same effects in Asian elephants.

Some work can be done to test this in the lab, Shapiro says. For instance, her team is already growing elephant cells in a lab dish. They can then test how those cells respond to things like possible changes in how or where in tissues a gene is active.

This allows Colossal to learn more about which genes to target without having to grow or experiment each time on a whole elephant.

Its team has already created elephant stem cells. These are the pluripotent type. That means they could potentially be used to create any type of cell (from skin or heart to bone or brain). That’s a key step toward assisting reproduction of an animal — with the goal of one day moving a gene-edited elephant embryo into an elephant to serve as its surrogate mother.

Complicating this last step is the fact that pregnancy in an Asian elephant can last almost two years. So taking each gene-edited elephant embryo to birth in such a surrogate would take far, far longer than bringing forth a woolly mouse. After all, the mouse’s pregnancy lasts just 18 to 21 days.

Another possible complication: The International Union for Conservation of Nature classifies Asian elephants as endangered with extinction. So this species’ rarity could limit anyone’s permission to use it for a surrogate mom.

For her part, Shapiro remains optimistic that something like de-extinction is possible.

In fact, one of her company’s other projects might succeed first: bringing back the dodo. After all, she notes, it lays an egg. That means it doesn’t need a surrogate mother.

Would our world nurture woolly mammoths?

Even assuming that all of this will be possible one day — and in numbers sufficient to create a healthy-size herd of woolly mammoths — other questions remain.

For one, scientists have shown that modern-day elephants are complex animals with established social and cultural knowledge. It’s something they pass down from one generation to the next. So, Gill asks, who’s to teach the first generation about “how to be a woolly mammoth?” 

The habitat that mammoths enjoyed has changed quite a bit, too, since their herds roamed the Pleistocene Epoch (which ended 11,700 years ago).

Back then, the tundra would have been full of life, Gill says. You might think of it as being much like Africa’s Serengeti is today.

This type of ecosystem — known as the mammoth steppe — was once the most widespread on Earth. Today’s northerly ecosystems, in contrast, host far fewer species. And the populations of species that can survive there also tend to be smaller.

But mammoths were keystone species, meaning ones that changed their environment. Mammoths may have made the mammoth steppe. And maybe it disappeared largely because the mammoths did.

So if mammoths made an ecosystem once, could they maybe do so again?

In theory, new mammoths could alter their ecosystem in ways that would nurture their reborn species, Gill says. And that idea is key to one of Colossal Bioscience’s goals: Bringing back herds of mammoths to again stamp down permafrost and help keep carbon stored in the ground. This might be one “old” way to protect against further climate change.

How likely is that? Right now, Gill admits, “we don’t actually know.”