In a feat right at the limit of our scientific capabilities, an international team of geneticists has recovered and sequenced the oldest DNA to date.
From the teeth of three ancient mammoths that roamed Siberia between 700,000 and 1.2 million years ago, researchers extracted extremely degraded DNA and reconstructed it to reveal a hitherto unknown lineage of genetic mammoths.
Previously, the oldest recovered DNA sample came from a horse bone found in the Yukon permafrost, which dates back to 560,000 to 780,000 years ago.
“This DNA is incredibly old,” said evolutionary geneticist Love Dalén of the Swedish Center for Paleogenetics. “The samples are a thousand times older than the Viking remains, and even predate the existence of humans and Neanderthals.”
About a million years ago, even woolly mammoths (Mammuthus primigenius) did not yet exist. The well-known and beloved beasts did not begin to emerge until about 800,000 years ago, living in the icy climates of the Earth until they finally became extinct about 4,000 years ago.
Because it is relatively recent, in geological times, and because they preferred cold habitats (which better preserve the remains), we know a little about these ancient creatures.
Woolly mammoths existed alongside Colombian mammoths (M. columbi), which inhabited North America and became extinct about 11,500 years ago.
Their predecessors, whose mammoths evolved into woolly mammoths, are less well known. We know that woolly mammoths are descended from steppe mammoths (M. trogontherii), which spanned most of Eurasia until about 200,000 years ago. We also thought that Colombian mammoths were descendants of steppe mammoths that had crossed into North America about 1.5 million years ago.
In an attempt to learn more about this ancestor, scientists turned their genealogy into a mammoth.
The three mammoth teeth from which they extracted the DNA were excavated decades ago and had been carefully stored in a museum collection. The youngest, 700,000 years old, belonged to a woolly mammoth, one of the first known. The two largest, more than a million years old, were expected to belong to the steppe mammoth.
Through careful restoration and comparative efforts, the researchers were able to gather and sequence the DNA that had been preserved inside the hard enamel of the animals ’teeth. The second oldest specimen of the three specimens, found at Adycha, proved this: it was very close to the steppe mammoth in morphology and DNA.
The oldest specimen, found in Krestovka and about 1.6 million years ago, surprised more. It turned out to belong to a hitherto unknown genetic mammoth lineage that deviated from a common ancestor more than 2 million years ago.
“This completely surprised us,” said geneticist Tom van der Valk of Uppsala University in Sweden.
“All previous studies have indicated that there was only one species of mammoth in Siberia at the time, called the steppe mammoth. But our DNA analyzes now show that there were two different genetic lineages, which we refer to here. like the Adycha mammoth and the Krestovka mammoth. We still can’t say for sure, but we think they can represent two different species. “
It gets even more interesting. By comparing the DNA of these ancient mammoths with those that came later, researchers found that it could have been the Krestovka mammoth that crossed the Bering Land Bridge in North America 1.5 million years ago. years, not the steppe mammoth.
The DNA of the Colombian mammoth has a mixture of Krestovka and woolly mammoth, suggesting that the two were bred when woolly mammoths migrated to North America, producing a hybrid.
“This is an important discovery,” said paleogenetics Patrícia Pečnerová of the University of Copenhagen in Denmark. “It appears that the Colombian mammoth, one of the most iconic species of the North American ice age, evolved through a hybridization that took place approximately 420,000 years ago.”
Adycha’s mammoth, while more in line with expectations, also had some secrets to reveal. By comparing its genome with that of woolly mammoths from 700,000 to a few thousand years ago, the team tried to understand how the woolly mammoth adapted to a frozen Arctic environment.
The traits associated with this adaptation – genes associated with thermoregulation, hair growth, circadian rhythm, and white and brown fat deposits – were already present in the Adycha genome, long before the woolly mammoth appeared. But animals also continued to evolve; the gene involved in temperature detection, for example, had more variants in later woolly mammoths.
Team techniques will not work for all the rest. The cold temperature of the permafrost slows down the degradation of DNA, so the remains of a similar age elsewhere would probably be too degraded; and, within the permafrost, there is a limit as to the recovery of this DNA.
“One of the big questions now is how far back in time we can go. We haven’t reached the limit yet,” said molecular archaeologist Anders Götherström of the Center for Paleogenetics.
“An instructed assumption would be that we could recover DNA that is 2 million years old and possibly up to 2.6 million. Before, there was no permafrost where ancient DNA could be preserved.”
Many preserved creatures of the Earth’s permafrost have been excavated. Research shows what remarkable discoveries may be hidden in bones previously considered too old to attempt to study.
The research has been published in Nature.