The teeth of mammoths buried in Siberian permafrost for more than a million years have yielded the world’s oldest DNA ever sequenced, according to a study released Wednesday, which illuminates a genetic reflector into the deep past.
Researchers said the three specimens, one roughly 800,000 years old and two over a million years old, provide important insight into giant mammals from the Ice Age, including the ancient heritage of the woolly mammoth.
The genomes far exceed the oldest previously sequenced DNA – a horse dating back between 780,000 and 560,000 years.
“This DNA is incredibly old. The specimens are a thousand times older than the remains of the Vikings, and even precede the existence of humans and Neanderthals, ”said Love Dalen, a professor of evolutionary genetics at the Center for Paleogenetics in Stockholm, senior author of the study published in the journal Nature.
Mammoths were originally discovered in the 1970s in Siberia and kept at the Russian Academy of Sciences in Moscow.
The researchers first dated the samples geologically, comparing them to other species, such as small rodents, which are known to be unique over time and to be found in the same sedimentary layers.
This suggests that the two mammals are ancient steppe mammoths more than a million years old.
The youngest of the trio is one of the earliest woolly mammoths yet to be found.
– DNA jigsaw puzzle –
They also extracted genetic data from tiny powder samples from each mammoth’s teeth, “basically like a pinch of salt that you would put on a dinner plate,” Dalen said at a news briefing.
Although broken down into very small fragments, scientists have been able to sequence tens of millions of chemical base pairs, which make up DNA strands, and conduct age estimates from genetic information.
This suggests that the oldest mammoth, named Krestovka, is even older at approximately 1.65 million years, while the other, Adycha, is about 1.34 million years old, and the youngest Chukochya is 870,000 years old.
Dalen said the disagreement of the oldest mammoth could be an underestimation in the process of finding DNA, meaning the creature is probably about 1.2 million years old, as geological evidence suggests.
But he said it was possible that the specimen was indeed older and that at one point it melted from the permafrost and then slammed into a younger layer of sediment.
The DNA fragments were like a jigsaw puzzle with millions of tiny pieces, “way, way, way smaller than you would get from modern high-quality DNA,” said lead author Tom van der Valk of the Science for Life Laboratory at Uppsala University.
Using the genome of the African elephant, a modern cousin of the mammoth, as a blueprint for their algorithm, the researchers were able to reconstruct parts of the mammoth’s genome.
The study found that the older mammoth Krestovka represents a previously unrecognized genetic lineage, which researchers estimated differed from other mammoths about two million years ago and was the ancestral home of those who colonized North America.
The study also found a lineage from a million-year-old Adycha steppe mammoth to Chukochya and other newer woolly mammoths.
He found variants of genes associated with life in the Arctic, such as hairiness, thermoregulation, fat deposits, and cold tolerance in older samples, suggesting that mammoths were already hairy long before the woolly mammoth appeared.
– Ice Age Giants –
Siberia alternated between dry and cold conditions of the ice age and warm, humid periods.
Now climate change is melting the permafrost and revealing more specimens, Dalen said, although heavier rains could mean the remains are being washed away.
He said that the new technologies mean that it may be possible to sequence the older DNA from the remains found in the eternal ice, which dates back 2.6 million years.
Researchers want to look at creatures like the ancestors of moose, muscox, wolves and lemmings, to shed light on the evolution of modern species.
“Giants of the Ice Age pushed genomics into deep time,” said Alfred Roca, a professor in the Department of Animal Sciences at the University of Illinois, in a commentary published in the journal Nature.
“The mammals that surrounded them could have their day soon.”
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