In an achievement 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 highly degraded DNA and reassembled it to reveal a previously unknown genetic mammoth line.
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 Center for Paleogenogenics in Sweden. “The monsters are a thousand times older than the remains of Viking, and even pre-date 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 animals first began to emerge about 800,000 years ago and lived in the frozen climate of the earth until they finally became extinct about 4,000 years ago.
Since it is relatively recent, in geological time, and because they prefer cold habitats (which better preserve the remains), we know quite a bit about these ancient creatures.
Wool mammoths exist alongside Columbian mammoths (M. columbi), which inhabited North America and became extinct about 11,500 years ago.
Their predecessors, the mammoths from which woolly mammoths evolved, are less well known. We know that woolly mammoths are descended from steppe mammoths (M. trogontherii), which roamed most of Eurasia until about 200,000 years ago. We also thought that Columbian mammoths are descended from steppe mammoths that migrated to North America about 1.5 million years ago.
In an effort to find out more about this ancestor, the scientists turned the giant genealogy register on its head.
The three giant teeth from which they extracted DNA were excavated decades ago and have been carefully preserved in a museum collection. The youngest, 700,000 years old, belonged to a woolly mammoth – one of the earliest known. The older two, more than 1 million years old, were expected to belong to the steppe mammoth.
Through careful repairs and comparative efforts, the researchers were able to summarize and sequence the DNA preserved in the hard enamel of the animals’ teeth. The second oldest of the three specimens, found in Adycha, pointed this out: it was very close to steppe in morphology and DNA.
The oldest specimen, found in Krestovka and dating from about 1.6 million years ago, was more surprising. It appears to belong to a previously unknown genetic mammoth lineage that deviated from a common ancestor more than 2 million years ago.
“It was a total surprise to us,” said geneticist Tom van der Valk of Uppsala University in Sweden.
“All previous studies indicated that at that time there was only one species of mammoth in Siberia, called the steppe mammoth. But our DNA analyzes now show that there were two different genetic descendants, which we refer to here as the Adycha mammoth. “We can’t say for sure yet, but we think it could represent two different kinds.”
It gets even more interesting. By comparing the DNA of these ancient mammoths with those that came later, the researchers found that it could have been the Krestovka mammoth that crossed the Bering Land Bridge to North America 1.5 million years ago, not the steppe mammoth. not.
The DNA of the Columbian mammoth contains a mixture of Krestovka and woolly mammoth, suggesting that the two bred when woolly mammoths migrated to North America and caused a hybrid.
“This is an important discovery,” said paleogeneticist Patrícia Pečnerová of the University of Copenhagen in Denmark. “It appears that the Columbian mammoth, one of the most iconic ice age species in North America, evolved through a hybridization that occurred about 420 thousand years ago.”
The Adycha mammoth, though 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 was adapted to a frozen Arctic environment.
The traits associated with the 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 emerged. But the animals also continued to evolve; the gene involved in observing temperature, for example, had more variants in later woolly mammoths.
The techniques of the team will not work for all remnants. The cold temperature of the permafrost slows down the degradation of DNA, so residues of a similar age from other sites are likely to be degraded; and within the permafrost there is a limit to how far back the DNA can be recovered.
“One of the big questions now is how far we can go back in time. We have not yet reached the limit,” said molecular archaeologist Anders Götherström of the Center for Paleogenogenics.
“An educated guess would be that we could recover DNA that is 2 million years old and possibly even go back as far as 2.6 million. Previously, there was no permafrost where old DNA could have been preserved.”
Many conservative creatures have been exhumed from the permafrost of the earth. The research shows that remarkable discoveries lurk in bones that were previously considered too old to try to study.
The research was published in Nature.