It is undoubtedly the hallmark of great scientists to recognize that they have made a mistake. “In 2005, I wrote that we couldn’t 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 a study that shatters ancient 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 tilt of the Earth in relation to the Sun.
Eske Willerslev was probably in the best position to deny his own predictions. In 2003, he published in Science the first analysis of environmental DNA (eDNA), taken not from a fossil, but from frozen sediments that have trapped the genetic heritage of extinct beings. It triggered a revolution combining ancient and environmental DNA, which has accelerated in recent months.
In the summer of 2021, this led, for example, to the description of the human populations having occupied the Denisova cave in the Russian Altai, during the last 300 millennia, even in the absence of fossils. Very recently, at the beginning of October, the DNA of diatoms a million years old had been described in marine sediments recovered in Antarctica. The all-time record for ancient DNA was held since early 2021 by teeth from Siberian mammoths over a million years old.
open forest
Eske Willerslev and her colleagues therefore take us twice as far back in time, and ever further north. A long-term scientific journey. “This is the longest study I have participated in”, said the researcher during a press conference call on Tuesday, December 6. The first sediment samples were recovered in 2006 from the northernmost region of Greenland. A desolate land, “a kind of Sahara in 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 deliver their tiny cargo of DNA, firmly attached – scientists speak of adsorption – to the grains of quartz and even more so to the clay. “This difficulty in extracting the DNA was also an indication of better conservation”, explains Karina Sand (University of Copenhagen), who finally found how to extricate the fragile molecule from it – which can therefore also be found by this means in regions where it would not have been protected by the cold. Sequencing platforms and bioinformatics comparison tools were then able to run at full speed.
You have 57.69% of this article left to read. The following is for subscribers only.