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WASHINGTON – Scientists have recovered the oldest DNA on record, extracting it from mammoth molars that roamed northeast Siberia up to 1.2 million years ago in research that broaden horizons to understand extinct species.
Researchers said on Wednesday they had recovered and sequenced DNA from the remains of three individual mammoths – elephant cousins who were among the large mammals that dominated Ice Age landscapes – buried in permafrost conditions conducive to preservation of old genetic material.
While the remains were discovered from the 1970s, new scientific methods were needed to extract the DNA.
The oldest of the three, discovered near the Krestovka River, was around 1.2 million years old. Another, near the Adycha River, was about 1 to 1.2 million years old. The third, near the Chukochya River, was about 700,000 years old.
“This is by far the oldest DNA ever to be recovered,” said evolutionary geneticist Love Dalén from the Center for Paleogenetics in Sweden, who led the research published in the journal Nature.
The oldest DNA so far has come from a horse that lived in the Canadian territory of the Yukon about 700,000 years ago. For comparison, our species, Homo sapiens, first appeared about 300,000 years ago.
DNA is the self-replicating material that carries genetic information in living organisms – a kind of model of life.
“This DNA has been extremely degraded into very small pieces, so we had to sequence several billion ultra-short DNA sequences in order to peel these genomes together,” said Dalén.
Most of the knowledge about prehistoric creatures comes from studying skeletal fossils, but there is a limit to what these can say about an organism, especially when it comes to genetic relationships and traits.
Ancient DNA can help fill in the blanks, but it is highly perishable. New, sophisticated research techniques allow scientists to recover ever-older DNA.
“That would be a wild guess, but a maximum of two to three million years should be doable,” Dalén said.
This could shed light on some bygone species but would leave many others inaccessible – including dinosaurs, which became extinct 66 million years ago.
“When we can get DNA over a timescale of a million years, we can study the process of speciation (formation of new species) in much more detail. Morphological analyzes of bones and teeth usually only allow researchers to study a handful of features in fossils, whereas with genomics we analyze tens of thousands of features, ”said Dalén.
Researchers obtained information on the evolution and migration of mammoths by comparing DNA to that of mammoths that lived more recently. The last mammoths disappeared around 4,000 years ago.
The oldest of the three specimens, the Krestovka mammoth, belonged to a previously unknown genetic line which, over 2 million years ago, diverged from the line that led to the well-known woolly mammoth.
Geneticist Tom van der Valk of SciLifeLab in Sweden, the study’s first author, said it appears members of the Krestovka lineage were the first mammoths to migrate from Siberia to North America on a land bridge now extinct about 1.5 million years ago, with mammoths migrating later about 400,000 to 500,000 years ago.
The Adycha mammoth line was apparently ancestral to the woolly mammoth, they discovered, and the individual Chukochya is one of the oldest known woolly mammoth specimens.
DNA analyzes have shown that genetic variants associated with enduring freezing climates such as hair growth, thermoregulation, fat deposits, cold tolerance and circadian rhythms were present long before the origin of the woolly mammoth.
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