A new record for the oldest DNA sequences: the million-year threshold crossed | Science | News | the sun

TheAnalyzes of three mammoth samples shed new light on the Ice Age, when large mammals prevailed, and the legacy of the woolly mammoth, whose last survivors just 4,000 years ago disappeared from Wrangel Island, off Siberia.

The genomes decoded far exceed the oldest DNA ever sequenced, the genome between 500,000 and 700,000 years old. Here DNA – the carrier of genetic information is called Genome – “Incredibly ancient. The specimens are a thousand times older than the remains of the Vikings, and even predate the existence of modern humans and Neanderthals,” Miracle Love Dalin, of the Stockholm Center for Paleontology, who supervised the study published in the review Temperate nature.

The fossils were discovered in the 1970s in Siberia, in permafrost (deep frozen ground, also called permafrost), and were kept at the Russian Academy of Sciences in Moscow. Researchers first succeeded in determining the history of teeth (molars) by comparing them with other species, such as small rodents, which are known to be unique for certain periods and found in the same sedimentary layers. These early comparisons indicate that the two large mammals were ancient steppe mammoths over a million years old. The “youngest” of the three, at about 800,000 years old, was the oldest woolly mammoth (a species that diverged from the steppe mammoth) ever discovered.

“a pinch of salt”

But the researchers went further and succeeded in extracting genetic data from small samples of tooth powder, “like a pinch of salt to season a dish,” Love Dalin, a professor of genetics, said at a press conference. Despite its deterioration, scientists have been able to sequence millions of base pairs, the building blocks of DNA, and estimate age from this valuable information, which is more accurate than geological evidence.

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Verdict: the oldest mammoth, called Krestovka, is even older than it was initially estimated at 1.65 million years; The second, Adicha, is 1.34 million years old. Chukuchia, the “younger”, is about 870,000 years old.

Its DNA fragments looked “like a jigsaw puzzle, with millions of little pieces, and many of them are much smaller than what you can get from high-quality modern DNA,” developed Tom van der Valk of Uppsala University in Sweden, lead author of the study. Using the genome of the African elephant, the cousin of the modern mammoth, researchers also discovered that the oldest, Krestovka, came from a hitherto unknown genetic line that would have deviated from other species there; it was about two million years old and then a North American colony. Further analyzes revealed genetic variations associated with life in the Arctic, such as hair, thermoregulation, or fat deposits, indicating that the mammoth was hairy long before the congeners appeared.

The melting of Siberian ice, linked to global warming, is revealing more and more fossils. A veritable mine also makes scientists eager to study the past of small animals, such as the ancestors of elk, musk ox or rodents. If genetics shed light on Ice Age megafauna, Alfred Rocca of the American University of Illinois said in a commentary posted on the sidelines of the study, “the small mammal clock might soon be ticking.”

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