Siberian mammoth molars yield oldest DNA ever recovered
Remains discovered in 1970s were entombed in permafrost conditions, preserving ancient genetic material
Scientists say they have recovered the oldest DNA on record, extracting it from the molars of mammoths that roamed northeastern Siberia up to 1.2 million years ago in research that broadens the horizons for understanding extinct species.
The researchers said on Wednesday they had recovered and sequenced DNA from the remains of three individual mammoths in Russia's extreme north.
The animals — elephant cousins that were among the large mammals that dominated ice age landscapes — had been entombed in permafrost conditions that helped preserve the ancient genetic material. While the remains were first discovered in the 1970s, new scientific methods were needed to extract the DNA.
The oldest of the three mammoths, discovered near the Krestovka river, was approximately 1.2 million years old. Another, from near the Adycha river, was about 1 million to 1.2 million years old. The third, from near the Chukochya river, was roughly 700,000 years old.
'Oldest DNA ever recovered'
"This is by a wide margin the oldest DNA ever recovered," said evolutionary geneticist Love Dalén of the Centre for Palaeogenetics in Sweden, who led the research published in the journal Nature.
Until this most recent discovery, the oldest DNA came from a horse that lived in Canada's Yukon territory about 700,000 years ago. In comparison, the human species, Homo sapiens, first appeared roughly 300,000 years ago.
"This DNA was extremely degraded into very small pieces, and so we had to sequence many billions of ultra-short DNA sequences in order to puzzle these genomes together," Dalén said.
Most knowledge about prehistoric creatures comes from studying skeletal fossils, but there is a limit to what these can tell about an organism, particularly when it comes to genetic relationships and traits.
Ancient DNA can help fill in the blanks but it's highly perishable. Sophisticated new research techniques are enabling scientists to recover ever-older DNA — a maximum of two to three million years old, Dalén said.
That could shed light on some bygone species, but it would leave many others unattainable — including the dinosaurs, which went extinct 66 million years ago.
According to Dalén, when DNA can be looked at on a million-year time scale, it allows scientists to study the process of speciation, or the formation of new species, in a much more detailed way.
"Morphological analysis on bones usually only allow researchers to study a handful of characteristics in the fossils, whereas with genomics we are analyzing many tens of thousands of characteristics," he said.
Insights into evolution, migration
The researchers gained insights into mammoth evolution and migration by comparing the DNA to that of mammoths that lived more recently. The last mammoths disappeared roughly 4,000 years ago.
The oldest of the three specimens, the Krestovka mammoth, belonged to a previously unknown genetic lineage that diverged from the lineage leading to the well-known wooly mammoth more than two million years ago.
Geneticist Tom van der Valk of SciLifeLab in Sweden, the study's first author, said it appears that members of the Krestovka lineage were the first mammoths to migrate from Siberia into North America over a now-disappeared land bridge about 1.5 million years ago, with wooly mammoths migrating about 400,000 to 500,000 years ago.
The Adycha mammoth's lineage apparently was ancestral to the wooly mammoth, researchers found, and the Chukochya individual is one of the oldest-known wooly mammoth specimens.
DNA analysis showed that genetic variants associated with enduring frigid climes such as hair growth, thermoregulation, fat deposits, cold tolerance and circadian rhythms were present long before the origin of the wooly mammoth.