From mammoth teeth, scientists just pulled DNA that's more than 1 million years old
- Scientists sequenced DNA from three ancient mammoth teeth found in Siberia.
- Some of the DNA was more than 1 million years old, making it the oldest DNA ever recovered.
- Genetics reveal these mammoths to be ancestors of both woolly mammoths and the mammoths that later occupied North America.
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More than 1 million years ago, mammoths traversed an ice-covered Siberia. The teeth and tusks they left behind were preserved in the region's permanently frozen ground.
Researchers recently extracted and mapped the DNA preserved in two mammoth molars from the region, with startling results. On Wednesday, they revealed that DNA is more than 1 million years old, making it the oldest DNA ever sequenced.
Before this finding, that record belonged to an ancient horse with DNA between 560,000 and 780,000 years old.
In their study about the mammoth teeth, the researchers reported that the molars came from two different types of mammoth. One species, the steppe mammoth, is well-known: its descendants were woolly mammoths. The other, according to Love Dale´n, a geneticist at the Center for Palaeogenetics in Sweden, is from a "previously unknown mammoth that lived in Siberia around 1.2 million years ago."
This second species, Dale´n told Insider, interbred with woolly mammoths about 420,000 years ago, which gave rise to the Columbian mammoths that went onto occupy North America.
Tracing mammoth ancestors using their DNA
The ancient molars themselves aren't new discoveries: Andrei Sher, a Russian paleontologist, found them in the 1970s.
But the new study, published in the journal Nature, pinpointed how old the teeth are for the first time. To accomplish this, Dalén's team first looked at the age of the rock deposits where Sher collected the teeth.
The researchers named the molar from the previously unknown mammoth species Krestovka, after the place it was found. The rock there is between 1.1 and 1.2 million years old. The other tooth, which the team named Adycha, was pulled from a rock layer dating back between 500,000 and 1.2 million years.
The researchers compared this geologic dating information with genetic data.
Over time, DNA builds up mutations: changes in a species' genetic sequence. Those mutations accrue at a fairly constant rate over time, so researchers can count the number of mutations to figure out how much time has passed since a given evolutionary event, like the point when a species split into two, for example.
Mammoths and living elephants diverged from a common ancestor around 5.3 million years ago, according to a genetic study from 2018. By calculating the number of mutations in the ancient mammoths' DNA, the study authors could estimate how much time had passed between that separation and the mammoth's birth.
"The more differences there are between lineages, the more time that has elapsed," Alfred Roca, an animal scientist from the University of Illinois at Urbana-Champaign who was not involved in the research, told Insider.
That method showed that the the Krestova specimen is about 1.65 million years old, while Adycha is around 1.34 million years old.
Dalén's team also pulled DNA from a third tooth found in Siberia named Chukochya. It was about 870,000 years old, likely from one of the oldest woolly mammoths.
The benefits of permafrost preservation
Dalén has worked with ancient rhino fossils, too. Two years ago, he co-authored a paper that looked at a 1.7-million-year-old rhino tooth. Although that specimen is older than the mammoth molars, Dalén's team was not able to recover DNA from it - only protein.
Proteins aren't as informative as DNA, since they only code for a tiny piece of an animal's genetic code.
However, DNA degrades over time, especially if it's exposed to heat or sunlight. That's why scientists had never previously found genetic molecules more than hundreds of thousands of years old. Siberia, however, offers a resting place for fossils that increases the chances the DNA inside can survive.
"Cold temperatures keep the DNA from degrading, much as a freezer keeps food from spoiling," Roca said.
Even so, the DNA in the mammoth teeth was very fragmented when the researchers pulled it out - "broken into tens of millions of small pieces," according to Dalén.
So analyzing it was a challenge, but the achievement creates new opportunities to study how ancient species interbred and evolved. Dalén's group showed it's possible to study the genes of creatures far older than scientists previously thought possible.
The study authors think that based on what they learned from this work, they'll be equipped to extract DNA that's even older from other fossils that may emerge from the permafrost.
"We haven't reached the limit yet. An educated guess would be that we could recover DNA that is 2 million years old, and possibly go even as far back as 2.6 million," Anders Götherström, a molecular archaeologist and co-author of the study, said in a press release. "Before that, there was no permafrost where ancient DNA could have been preserved.
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