According to a study published on Wednesday, the teeth of mammoths buried in Siberian permafrost for more than a million years have produced the oldest DNA ever sequenced, which has shed light on a genetic focus in the deep past.
The researchers said the three specimens, one about 800,000 years old and two more than a million years old, provide an important insight into giant mammals from the ice age, including the ancient heritage of the mammoth. woolly.
Genomes far exceed the DNA sequenced above: a horse dating back between 780,000 and 560,000 years ago.
“This DNA is incredibly old. The samples are a thousand times older than the Viking remains, and even predate the existence of humans and Neanderthals, ”said Love Dalen, a professor of evolutionary genetics at the Stockholm Center for Paleogenetics and lead author of the study published in the journal. Nature.
Mammoths were originally discovered in the 1970s in Siberia and were held at the Russian Academy of Sciences in Moscow.
The researchers first dated the specimens geologically, with comparisons with other species, such as small rodents, known to be exclusive to particular time periods and found in the same sedimentary layers.
This suggested that two of the mammals were ancient steppe mammals over a million years old.
The youngest of the trio is one of the first woolly mammoths to be found so far.
DNA puzzles
The researchers also extracted genetic data from small dust samples from each mammoth tooth, “essentially like a little salt you would put on your dinner plate,” Dalen told a news conference.
A woolly mammoth tusk emerges from the permafrost in central Wrangel Island, northeastern Siberia. Analysis of the teeth of the animals has yielded the oldest DNA ever sequenced [Love Dalén via AFP]
Although it had degraded into very small fragments, scientists were able to sequence tens of millions of pairs of chemical bases, which form the strands of DNA and make age estimates from genetic information.
This suggested that the oldest mammoth, named Krestovka, is even larger by about 1.65 million years old, while the second, Adycha, is about 1.34 million years old and the youngest Chukochya is 870,000 years old. .
Dalen said the discrepancy between the oldest mammoth could be an underestimation in the DNA dating process, meaning the creature was probably about 1.2 million years old, as geologic evidence suggests.
But he said it was possible that the specimen was actually older and that it had thawed from the permafrost at some point and turned into a younger layer of sediment.
The DNA fragments were like a puzzle with millions of small pieces, “way, way, much smaller than you would get from modern, high-quality DNA,” said lead author Tom van der Valk, of Science for Life Laboratory, Uppsala University. .
Using a genome of an African elephant, a modern relative of the mammoth, as a model for its algorithm, the researchers were able to reconstruct parts of the mammoth’s genomes.
The study found that Krestovka’s oldest mammoth represents a previously unrecognized genetic lineage, which researchers estimated to have deviated from other mammoths about two million years ago and was ancestral to those who colonized America. of the North.
The study also traced the lineage from the millennial steppe mammoth of Adycha to Chukochya and other more recent woolly mammoths.
He found gene variants associated with Arctic life, such as hairiness, thermoregulation, fat deposits, and cold tolerance in the oldest specimen, suggesting that mammoths were already furry long before the woolly mammoth.
Ice Age Giants
Siberia has alternated between the conditions of the dry and cold glacial era and the warm and humid periods.
Now, climate change is melting the permafrost and revealing more specimens, Dalen said, though increased rainfall could mean the remnants are being wiped out.
He said new technologies mean it may be possible to sequence even older DNA from remains found in permafrost, which dates back 2.6 million years.
Researchers want to look at creatures such as the ancestors of moose, mosses, wolves and lemmings, to shed light on the evolution of modern species.
“Genomics has been pushed deep into time by the giants of the ice age,” Alfred Roca, a professor in the Department of Animal Science at the University of Illinois, said in a comment published in Nature.
“The small mammals that surrounded them could soon have their day.”