Shocking skin of 52,000-year-old woolly mammoth could change our knowledge of ancient DNA

The leathery strip of skin from a 52,000-year-old woolly mammoth with a mullet-like haircut isn’t much to look at, says geneticist Olga Dudchenko, but the information it contains is priceless.

The sample comes from a female mammoth unearthed in the permafrost of Siberia in 2018. It also includes the hairy skin around the left side of her head, including one ear.

“It’s not necessarily something you see and are amazed by,” said Dudchenko, of the Baylor College of Medicine in Texas. As it happens host Peter Armstrong.

“The real surprise was inside.”

When Dudchenko and her colleagues zoomed in on the specimen, 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 CellThe findings not only paint an unprecedentedly detailed genetic picture of the woolly mammoth, but could also have implications for how we understand other forms of ancient life.

“We are dealing with a new type of fossil,” Dudchenko said. “I hope that many more samples like this will be found, including mammoths and other species.”

The Science of Dried Meat

Scientists have found and studied ancient DNA before. But because DNA molecules begin to break 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 at the back, inspiring the scientists who found it to name it after the famous mullet-headed British footballer.

The mammoth’s skin cells, preserved by permafrost, remained intact. And inside them, Dudchenko and her colleagues found fossilized chromosomes, or packets of DNA, frozen in place for several millennia.

The team suspects that the chromosomes were held together because the mammoth’s remains were naturally freeze-dried by the permafrost that covered its body after it died. The cold temperatures slowed the movement of the molecules as they fell apart, and the dry tundra dehydrated the skin, essentially turning it into a big hunk of dried meat.

“Jokes aside, there’s a lot of science behind dried meat … and it has everything to do with how you remove water,” Dudchenko said. “That gave us a hint that maybe this is also something that’s behind this kind of exceptional level of preservation in this particular mammoth.”

To test their theory, the scientists used freeze-dried beef and went to great lengths to destroy it.

“We shot it with a hunting rifle. We drove over it in 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 according to a press release.

“Every time, the dried meat broke into little pieces — shattering like glass. But at the nanoscale, the chromosomes were intact, unchanged. That’s why these fossils can survive. That’s why 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, discovered in Siberia in 2010 and one of the best-preserved mammoths ever found.

“What we show here is that this information about the arrangement of DNA in very ancient species has not been erased from history,” Dudchenko said.

What have scientists learned about mammoths?

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

The scientists were also able to determine which genes were active in the mammoth when it died, which explains some important differences between elephants and mammoths.

For example, the mammoth had genes that regulated the development of sweat glands and hair follicles, which could explain why the woolly mammoth was so woolly and how it survived cold environments.

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

“The methodology they used could change the way we obtain fossil DNA from more difficult remains,” Poinar, who has studied mammoths using the isotopes in their tusks, told CBC in an email.

By mapping the genetic differences between elephants and mammoths, Poinar said, scientists can “unravel the behavioral differences between the two species and how they diverged.”

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

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

“We didn’t set that goal as part of this work,” she said. “But the basic biology that we learned about the mammoths from this study is, I think, a step in that direction.”