最古のＤＮＡ発見、２００万年前の生態系ひもとく　グリーンランド

【コペンハーゲンＡＦＰ＝時事】デンマーク領グリーンランド最北端の氷河期の堆積層から、これまで採取された中で最古となる２００万年前のＤＮＡが見つかった。コペンハーゲン大学などの研究チームが７日、発表した。古遺伝学の新たな扉を開く発見だ。（写真は、グリーンランド北部のカプ・コベンハブン堆積層で調査を行う研究者）
　英科学誌ネイチャーに掲載された論文を共同執筆したコペンハーゲン大のミッケル・ウィンザー・ペデルセン氏は、「遺伝子研究における壁を打ち破りつつある」「ＤＮＡ生存の境界は１００万年だと長年思われていたが、その倍に延びた」とＡＦＰに語った。
　現在は極砂漠となっている人里離れた無人地帯で凍結保存されていたＤＮＡの状態は非常に良く、研究チームは最新技術によって、４１個の断片が、これまで最古とされていたシベリアのマンモスから採取されたＤＮＡより１００万年以上古いことを突き止めた。
　２００６年に始まった研究では、１０２種の植物を発見。２００万年前のグリーンランド北部の生態系を再構築することに成功した。それは「マストドンやトナカイ、ノウサギが駆け回り、多種多様な植物の生い茂る森林風景」だという。
　ゾウの祖先に当たる大型哺乳類マストドンの存在がこれほど北方で確認されたのは初めてで、特に注目に値する。この発見により、種の適応性についてより多くの知見が得られた。
　２００万年前のグリーンランドは、現在と比べて気温が１１～１７度高かった。しかも緯度が高いため、夏は太陽が沈まず、冬は昇ることがない。
　「このような環境、このような種の混在は、現在の地球上ではどこにも見当たらない」とウィンザー・ペデルセン氏は指摘。「種の可塑性、つまり種が実際にさまざまな気候タイプにどのように適応できるかは、これまで考えられていたものとは異なるかもしれない」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/12/09-18:38）

Scientists in Greenland announced Wednesday they had found DNA dating back two million years -- the oldest ever extracted -- in sediment from the Ice Age, opening a new chapter in paleogenetics.
We are breaking the barrier of what we thought we could reach in terms of genetic studies, said Mikkel Winther Pedersen, co-author of a new study published in science journal Nature.
It was long thought that one million years was the boundary of DNA survival, but now we are twice as old as that, told AFP.
They found the DNA fragments in sediment from the northernmost part of Greenland known as Kap Copenhagen, said the University of Copenhagen lecturer.
The fragments come from an environment that we do not see anywhere on Earth today, he added. Frozen in a remote unpopulated area, the DNA had been very well preserved.
New technology enabled the scientists to determine that the 41 fragments were more than a million years older than the oldest known DNA, from a Siberian mammoth.
They had to first determine whether there was DNA hidden in the clay and quartz, then see whether it could be removed from the sediment to examine it.
The method used provides a fundamental understanding of why minerals, or sediments, can preserve DNA, said Karina Sand, who heads the geobiology team at the University of Copenhagen and who took part in the study.
It's a Pandora's box we're just about to open up, she added.
- Species adaptability -
The rivers running through the environment transported minerals and organic material into the marine environment and this was where these terrestrial sediments were deposited, said Winther Pedersen.
Then, at some point around two million years ago, this land mass beneath the water was raised up and became a part of North Greenland, he explained.
Today, Kap Copenhagen is an Arctic desert, where different types of deposits, including plant and insect fossils preserved in excellent condition, have already been discovered.
But scientists hadn't tried to establish the fossils' DNA, and very little was known about the presence of animals at the time.
The research team, which began its work in 2006, has now made it possible to paint a picture of what the region looked like two million years ago.
We had this forested environment with mastodons and reindeer and hares running around in the landscape together with a lot of different plant species, he said, they had found 102 different kinds of plant.
The presence of mastodons was particularly noteworthy, he added, never having been found so far north before. The discovery has also given researchers more information about the adaptability of species.
Two million years ago, Greenland had temperatures 11 to 17 degrees warmer than today, but at its latitude, the sun doesn't set in summer nor rise in winter.
We don't see this environment anywhere, this mix of species anywhere on Earth today, said Winther Pedersen.
The plasticity in species, how species are actually able to adapt to different types of climate, might be different than what we previously thought.
And obviously, it makes us look for newer and older sites.
There are several different sites across the world that actually have geological deposits that go this far back. And even further back, ha added.