Scientists have for the first time been able to collect and analyse DNA from more than 1m years ago, after extracting genetic material from the remains of mammoths found buried in the Siberian permafrost.
Love Dalén of Stockholm’s Centre for Palaeogenetics, who led the study published in Nature, said the DNA taken from fossilised teeth was the oldest ever discovered, beating the previous record of 700,000 years from a horse bone found in the Canadian Arctic.
Adrian Lister, a co-author from London’s Natural History Museum, said: “With million-year-old DNA we can extend [research] beyond the date of origin for many iconic species like the mammoth.
“We can track how species evolve and how their adaptations have arisen.”
The research team extracted DNA from three ancient mammoth molars that had been stored in a Moscow freezer since their excavation in Siberia by Soviet palaeontologists in the 1970s. Sophisticated genetic analysis would have been far beyond the capabilities of the scientists at the time.
As climate change begins to melt the permafrost, mammoth tusks and bones are being discovered at an increasing rate across Siberia, including Wrangel Island where the last of the elephantine creatures lived about 4,000 years ago.
Even with today’s gene-sequencing instruments the project was a challenge. The little surviving DNA had broken down into a large number of tiny molecular pieces.
Using a combination of geological and chemical techniques, the scientists concluded that the youngest tooth was 700,000 years old, the next dated back 1m years and the oldest 1.2m years.
After the genetic codes had been read, the researchers reconstructed the mammoths’ genomes using computer programs that stitched together overlapping DNA sequences — guided by the known genomes of modern elephants and more recent mammoths.
The DNA analysis also revealed that the oldest tooth came from a previously unknown species that the researchers called the Krestovka mammoth after the place it was found.
“This came as a complete surprise,” said Tom van der Valk of the Centre for Palaeogenetics. “All previous studies have indicated there was only one species of mammoth in Siberia at that point in time, called the steppe mammoth.”
The two types of ancestral mammoth later gave rise to woolly mammoths of the Canadian and Siberian Arctic and the Columbian mammoth that roamed the more temperate regions of North America during the last ice age.
Gene variants associated with Arctic life such as hair growth, thermoregulation, fat deposits and cold tolerance were already present a million years ago, well before the origin of the woolly mammoth. These results indicate that most adaptations in the mammoth lineage happened slowly and gradually over time.
The scientists believe similar studies could be carried out on other species to shed light on the period of rapid climatic and evolutionary change about 1m years ago.
“One of the big questions now is how far back in time we can go,” said Anders Götherström of the Centre for Palaeogenetics. “An educated guess would be that we could recover DNA that is 2m years old, and possibly go even as far back as 2.6m. Before that, there was no permafrost where ancient DNA could have been preserved.”
The oldest human DNA recovered so far comes from Spain and dates back about 400,000 years. Dalén said it might be possible to obtain an older sample from fossilised human remains stored in permafrost “but nothing has been found so far”.