1.6 million-year-old mammoth DNA reveals lineage we didn’t even know existed

When Love Dalén started studying ancient DNA as a doctoral student. a student in 2002, one of her colleagues suggested working on lemmings, small arctic rodents, and 90s video game icons. “Everyone makes mammoths,” she told Dalén, “c ‘is very competitive ”. The towering ancient proboscidians have captivated the imagination of the public and scientists for years – and when an opportunity presented itself for Dalén to study the famous woolly mammoth, he couldn’t resist. He wanted to understand why the creatures had become extinct.

But on Wednesday, Dalén and 21 other scientists looked at the other end of the woolly mammoth’s timeline: its origin. In a landmark article, published in the journal Nature, the team announces the recovery of DNA from mammoth specimens over a million years old – shattering the record for the oldest ancient DNA ever sequenced in nearly 900,000 years.

“This is an incredible article,” says Sally Wasef, a former DNA researcher at Griffith University in Australia. She is not affiliated with research.

The advances are twofold. First, the team was able to isolate short fragments of degraded DNA from tooth samples and obtain the genetic code through recent improvements in sequencing techniques and data analysis.

To sequence ancient DNA, the team looked at mammoth molars from three different mammoths discovered in Siberian permafrost decades ago. “We knew some of these teeth were from the first 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 collaborators in Russia for study. For a megaannum, the molars were protected from degradation thanks to the freezing temperatures present in the high latitudes of Siberia.

DNA degradation places an upper limit on how far scientists can look. Over time, DNA breaks down into tiny fragments which are then also mixed with many other DNA in the environment. “It becomes difficult 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 degraded for scientists to reconstruct.

In this new research, the team was operating at the limit. Using high-throughput sequencing and advanced computer analysis, the team assembled DNA from three specimens, using modern elephant genomes as a template. It also helped to age the beasts. Two of the samples, 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 over a million years ago using the three samples. Krestovka’s data indicated a whole new line of mammoths, hitherto unknown to science. It was a surprise for the team.

“We thought that anything going back about a million years would be the ancestors of the woolly mammoth,” notes Dalén. “It turns out that there were two different types of mammoths” roaming around Siberia a million years ago.

The team couldn’t get enough data to really say anything about Krestovka’s lineage – there isn’t enough DNA to examine the genes – but they were able to show that Krestovka didn’t. not contributed to the origin of the woolly mammoth.

On the contrary, it probably separated from the ancestor of the woolly mammoth about 2 million years ago and then gave birth to the Colombian mammoth – a species that existed in North America, where the climate was warmer. The Colombian mammoth got there about 1.5 million years ago, so the timelines match perfectly.

About 1.4 million years later, the woolly mammoth found its way to North America, and the Krestovka lineage and the woolly mammoth may have crossed each other to give birth to the Colombian mammoth. The team explains that along the way this interbreeding happened, but there is still work to be done to understand the origins of the Colombian mammoth.

Both breakthroughs will help advance paleogenomics, the study of ancient DNA from extinct species.

Wasef notes that the techniques used to isolate and sequence mammoth DNA could also be useful in analyzing ancient DNA from elsewhere in the world. However, permafrost is probably the only place we can look a million years into the past. Warmer climates like Australia, where Wasef is based, don’t preserve DNA as well – but she hopes she can apply the techniques to her own work.

Dalén’s interest lies in understanding the emergence of species in the Early and Middle Pleistocene, around the same time as mammoths. “In the future, it will be really interesting to study evolution at this timescale in other species as well,” he says.

Oddly enough, that could mean coming full circle. Maybe even go back to lemmings. But don’t cancel the woolly ones yet.

“We’re not done with mammoths either,” says Dalén. “There is a lot to do.”