Jerky-like skin of a 52,000-year-old woolly mammoth could change what we know about ancient DNA

The leathery strip of skin from a 52,000-year-old woolly mammoth sporting a mullet-like hairdo isn't much to look at, says geneticist Olga Dudchenko — but the information it contains is invaluable. 

The sample was taken from a female mammoth unearthed from Siberian permafrost in 2018, and includes the hairy skin around the left side of its head, including an ear. 

"It's not necessarily something that, you know, you would see and you'd just have your mind blown," Dudchenko, of the Baylor College of Medicine in Texas, told As It Happens guest host Peter Armstrong.

"The real surprise sort of lay within."

When Dudchenko and her colleagues zoomed in on the sample they found fossilized chromosomes so perfectly preserved that researchers were able to reconstruct the woolly mammoth's genome in 3D for the first time.

Published in the journal Cell, the findings not only paint an unprecedentedly detailed genetic picture of the woolly mammoth, but could have implications for how we understand other forms of ancient life.

"We are dealing with a new type of fossil," Dudchenko said. "There are going to be many samples like this, I hope, yet to be found for mammoths and other species as well."

The science of jerky

Scientist have found and studied ancient DNA before. But because DNA molecules start breaking down immediately after death, the samples so far have been highly fragmented, and learning from them is like trying to reconstruct a stained-glass mural from broken shards.

That all changed with the discovery of Chris Waddle, a woolly mammoth found in Siberia six years ago. Its skin is covered in hair that appears longer in the back, inspiring the scientists who found it to name it after the famously mulleted British soccer player.

The mammoth's skin cells, preserved by permafrost, remained intact. And within them, Dudchenko and her colleagues found fossilized chromosomes, or packages of DNA, frozen in place over the course of several millennia.

The team suspects the chromosomes held together because the mammoth's remains were naturally freeze-dried by the permafrost that covered its body after it died. The low temperatures slowed the motion of the molecules as they broke apart, and the dry tundra dehydrated the skin, essentially turning it into a big piece of jerky.

"Jokes aside, there is a lot of science behind jerky … and it has all to do about how you remove water," Dudchenko said. "That kind of gave us a hint that this may be something that's also behind this kind of exceptional level of preservation in this particular mammoth."

To test their theory, the scientists used freeze-dried beef jerky — and did their darnedest to destroy it.

"We fired a shotgun at it. We ran over it with a car. We had a former starting pitcher for the Houston Astros throw a fastball at it," co-author Cynthia Pérez Estrada of Rice University said in a press release.

"Each time, the jerky broke into tiny bits — shattering like a glass. But at the nano-scale, the chromosomes were intact, unchanged. That's the reason these fossils can survive. That's the reason that they were there, 52,000 years later, just waiting for us to find them."

The team also found intact chromosome fossils in the 39,000-year-old remains of another mammoth, Yuka, who was discovered in Siberia in 2010 and is one of the best preserved mammoths ever found.

"What we're showing here is this type of information about the arrangement of DNA in very old species has not been erased from history," Dudchenko said. 

What did scientists learn about mammoths?

By reconstructing the genome, the team determined that woolly mammoths have 28 chromosomes, just like their closest living relatives, Asian elephants.

The scientists were also able to determine which of the mammoth's genes were active when it died, helping to explain some of the key differences between elephants and mammoths. 

For example, the mammoth had genes switched on that regulate the development of sweat glands and hair follicles. This could potentially explain why the woolly mammoth was so woolly, and how it survived cold environments.

Hendrik Poinar, an evolutionary biologist at McMaster University in Hamilton, Ont., who was not involved in the study, called it "a fantastic piece of work."

"The methodology they used may be something that changes the way we access fossil DNA from more difficult remains," Poinar, who has studied mammoths using the isotopes in their tusks, told CBC in an email.

By figuring out the genetic differences between elephants and mammoths, Poinar says scientists "can begin to unravel behavioural differences between the two species and how they've diverged."

This, he says, brings us one step closer to "de-extincting" the species — referring to ongoing efforts to create an elephant-mammoth hybrid using mammoth DNA.

Dudchenko says bringing the mammoth back is not one of her team's goals.

"We have not set out as part of this work to do that," she said. "But the basic biology that we learned about the mammoths from this study is, I think, a step in that direction."