Admitting that they have made a mistake is undoubtedly the hallmark of great scientists. “In 2005 I wrote that we could not access DNA more than a million years old. Obviously, I was wrong. » And Eske Willerslev (University of Cambridge) is delighted: at the head of an international team, he publishes in the journal Nature of December 8 an investigation that smashes old DNA records. And makes it possible to describe not an individual, but an entire ecosystem, the fauna and flora of northern Greenland two million years ago, when the region was on average about ten degrees warmer than today.hui – due to the position and slope of Earth in relation to the Sun.
Eske Willerslev was probably best placed to deny his own predictions. In 2003 he published i Science the first analysis of environmental DNA (eDNA), taken not from a fossil, but from frozen sediments that have captured the genetic heritage of extinct creatures. That sparked a revolution combining ancient and environmental DNA that has accelerated in recent months.
In the summer of 2021, for example, this led to the description of the human populations that had occupied Denisova Cave in the Russian Altai over the past 300 millennia, even in the absence of fossils. Very recently, in early October, DNA from diatoms that were a million years old had been described in marine sediments found in Antarctica. The all-time record for ancient DNA was held since early 2021 by teeth from Siberian mammoths over a million years old.
Eske Willerslev and her colleagues therefore take us twice as far back in time, and even further north. A long-term scientific journey. “This is the longest survey I have participated in”, the researcher said during a press conference on Tuesday, December 6. The first sediment samples were found in 2006 from the northernmost region of Greenland. A wasteland, “a kind of Sahara under polar conditions, where only lichens and mosses remain”describes the researcher.
But until a handful of years ago, these samples taken from the permafrost refused to hand over their small cargo of DNA, which was firmly attached—the researchers talk about adsorption—to the quartz grains and even more so to the clay. “This difficulty in extracting the DNA was also an indication of better preservation”, explains Karina Sand (University of Copenhagen), who finally figured out how to remove the fragile molecule from it – which can therefore also be found in that way in areas where it would not have been protected by the cold. Sequencing platforms and bioinformatics comparison tools could then run at full speed.
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