Ancient DNA was recovered from three giant samples.
Beth Zaiken / Center for Paleogenetics
When Love Dalén first began studying with ancient DNA as a Ph.D. student in 2002, suggested one of his colleagues work on lemmings, the little arctic rodents and video games from the 90s. “Everyone does mammoths,” she told Dalén, “it’s very competitive.” The sly, old proboscideans captured the imagination of the public and scientists for years – and when Dalén came up with an opportunity to study the famous woolly mammoth, he could not resist it. He wanted to understand why the creatures became extinct.
But on Wednesday, Dalén and 21 other scientists looked at the other side of the woolly mammoth’s timeline: its origins. In a historiographical article published in the journal Nature, the team announces that they have recovered DNA from mammoth samples more than a million years old, destroying the record of the oldest ancient DNA traced back nearly 900,000 years .
“This is a wonderful article,” says Sally Wasef, an ancient DNA researcher at Griffith University in Australia. She is not involved in the research.
The breakthroughs are twofold. First, the team was able to isolate short, degraded DNA fragments from tooth samples and obtain the genetic code through recent improvements in sequence and data analysis techniques.
To sequence the ancient DNA, the team examined mammoth tusks of three different mammoths excavated in the Siberian permafrost several decades ago. “We knew that some of these teeth were from the earliest woolly mammoths,” says Dalén. He says the team obtained ‘small pieces of the roots of these teeth’, which usually weigh a few kilograms, from their colleagues in Russia for study. For a large year, the polling stations were protected from deterioration thanks to the freezing cold temperatures at Siberia’s high latitudes.
A mammoth fangs on Wrangel Island, the location of the last known woolly mammoths about 2,500 years ago.
Love Dalén
DNA degradation places an upper limit on how far back scientists can look. Over time, DNA breaks down into small fragments that are then mixed with many other DNAs from the environment. “It’s starting to get hard to see the difference between mammoth DNA, bacterial DNA, human DNA and plant DNA,” says Dalén. After about 1.5 million years, it becomes too degenerate for scientists to work together again.
In this new research, the team worked on the extreme frontier. Using high-throughput sequencing and advanced computer analysis, the team collaborated on DNA samples from three samples and used modern-day elephant genomes as blueprints. It also aged the animals. Two of the monsters, named Krestovka and Adycha, were 1.65 million and 1.34 million years old, respectively. A third, younger specimen, Chukochya, was 870,000 years old.
The DNA sequence also led to the second breakthrough: the team was able to assess the evolution and speciation of mammoths more than a million years ago using the three samples. Krestovka’s data pointed to a completely new generation of mammoths, previously unknown to science. It was a surprise for the team.
“We thought everything around a million years ago would be the ancestors of the woolly mammoth,” Dalén notes. ‘It seems that a million years ago there were two different kinds of mammoths in Siberia.
The team could not get enough data to really say anything about what Krestovka’s genus looked like – there is not enough DNA to look at the genes well – but they could show that Krestovka did not contribute to the origin of the wool. not. mammoth.
On the contrary, it probably split from the ancestor of the woolly mammoth about 2 million years ago and then gave rise to the Columbia mammoth – a species that existed in North America, where the climate was warmer. The Columbia mammoth arrived there about 1.5 million years ago, so the timelines agree neatly.
About 1.4 million years later, the woolly mammoth found its way to North America, and the Krestovka lineage and woolly mammoth may have moved in to give rise to the Columbian mammoth. The team argues that this crossing took place en route, but that more work needs to be done to understand the origins of the Columbian mammoth.
Both breakthroughs will contribute to the advancement of paleogenomics, the study of ancient DNA of extinct species.
Wasef taking note of the techniques used to isolate and sequence the mammoth DNA can also be helpful in analyzing ancient DNA from elsewhere in the world. However, the permafrost is probably the only place we can look a million years in the past. Warmer climates like in Australia, where Wasef is based, do not preserve DNA as well – yet she hopes to be able to apply the techniques to her own work.
Dalén’s interest lies in understanding how species originated in the early and middle Pleistocene, about the same time as the mammoths. “It will be really interesting in the future to investigate evolution on this time scale in other species as well,” he says.
Oddly enough, this could mean you have to become full circle. Maybe even back to the lemmings. But do not write off the woolly yet.
“We are not done with the mammoths either,” says Dalén. “There’s quite a lot to do.”