The oldest DNA was found in mammoth teeth/kloc-0.0 million years ago.

This is the mammoth of Siberian grassland 6.5438+0 million years ago. They have many genes that adapt to low temperature, and these genes help the later true mammoths thrive. Recently, scientists have sequenced the oldest DNA at present, and this painting is based on newly acquired knowledge.

Cartography: Beth Zaken, Center for Paleogenetics

Michael gray Shike wrote it.

Scientists sequenced the oldest DNA so far, breaking through the landmark boundary in ancient genome research, and opening a new window for studying the evolution of North American behemoths (Colombian mammoths and real mammoths) extinct during the Ice Age.

This research is unlikely to bring us a sensation like Jurassic Park, and it is not the first time that scientists have sequenced the mammoth genome. As for the resurrection of mammoths, it is far away. In fact, the object of this study is DNA 6.5438+0 million years ago, which has set a milestone for the rapid development of ancient DNA research and almost doubled the oldest genome sequencing record. The research results were published in the February 17 issue of Nature.

DNA comes from three molars of mammoths; In the early 1970s, Russian paleontologist Andrei Schell, a legend in the field of mammoth research, discovered these molars. The researchers estimate that the youngest of these three teeth came from 500,000 to 800,000 years ago, and the other two came from 654.38+0,000 to 654.38+0.2 million years ago. The second oldest sequenced DNA comes from horse fossils in Yukon, Canada nearly 700,000 years ago.

"It can be said that from an evolutionary point of view, breaking the magic barrier of more than 1 10,000 years is equivalent to opening a new time window," said Tom van Vander Waals, the main author of the study. He is a bioinformatician at Uppsala University and conducts research at the Paleogenetics Center in Stockholm, Sweden.

The research results add amazing details to scientists' understanding of the evolution of North American mammoths. First of all, the ancient DNA in teeth strongly proves that one of the main species of North American mammoths, the Colombian mammoth, is a hybrid, which appeared 400,000 to 500,000 years ago. The reason for this conclusion is that the older DNA in the study magically appeared before this hybrid. "When studying higher organisms such as vertebrates, the sampling of species must be after it appears," said Love Dalén, a geneticist and co-author of the Center for Paleogenetics.

The longer DNA records can be traced back, the more scientists can understand the evolution process. The author of the study said that the success of this study also means that, ideally, scientists can study the evolution process more deeply, even going back millions of years. Until then, the DNA will be too small to recombine. )

The study of teeth began on 20 17, when the center of paleogenetics received a tooth sample from the Russian Academy of Sciences. In geneticist patricia Pei? Led by nerová, the research team wore protective clothing (which is familiar to people who have experienced the COVID-19 epidemic) and ground 50 mg of bone powder from each sample. Then, Pe? Nerova carefully extracted a small amount of DNA and extracted a series of chemical solutions from each pinch of powder; DNA is concentrated in droplets the size of pepper. Pe？ Nerová is now a postdoctoral student at the University of Copenhagen in Denmark.

"Basically, I'm like in a cocoon, wearing masks and masks to minimize pollution," Pe? Nerova said: "Stop a (human) cell from falling into a test tube" and destroy the sample.

After several weeks of calculation, the research team can accurately identify mammoth DNA fragments as short as 35 base pairs and draw them into a genome of more than 3 billion bases.

Surprise of DNA sequence

This new study explains how North American mammoths evolved. To the researchers' shock, the newly studied DNA sequence is very old, even before the appearance of the Colombian mammoth, which gives scientists a new understanding of the evolution of mammoths. Columbia mammoth is one of the two main mammoth species in North America.

10.5 million years ago, close relatives of European and Asian mammoths set out from Siberia and crossed the continental bridge now covered by the Bering Strait to reach North America. These new immigrants became the later Colombian mammoths. About 654.38 million to 200,000 years ago, mammoths in North America were mainly divided into two types: the real mammoth in the north and the Colombian mammoth in southern Mexico. The researchers also learned from past genetic analysis that the two mammoths have crossed.

Paleontologists always distinguish different species by their unique upper molars. According to the tooth fossils of mammoths, traditionally, paleontologists speculated that the mammoths that appeared in North America about 6.5438+0.5 million years ago were Colombian mammoths. However, although the fossil record shows continuity, some changes have taken place in the gene record in the new DNA research.

The genomes of the two mammoths in the new study belong to the later real mammoth pedigree, but the oldest tooth (found near the Ka River in Christoph, which scientists call "Christophka") seems to belong to a previously unknown gene pedigree. About 6.5438+0.5 million years ago, this pedigree was separated from the gene pedigree containing two other teeth.

On Vrangel Island in the northeast of Siberia, sometimes the tusks of real mammoths appear in permafrost. Wrangell Island is one of the last shelters for mammoths. Some mammoths survived to 2500 BC, so this became the discovery place of mammoth DNA.

Photography: love DAL? ordinary

Vander Waals's team compared the mysterious mammoth genome with the previously sequenced Colombian mammoth DNA, and reached a surprising conclusion: the Colombian mammoth appeared 400,000 to 500,000 years ago, and it was a hybrid of the mammoth Christoph Kalma and the mammoth Siberia. This happened somewhere in Siberia, North America or the Bering Continental Bridge.

About 200,000 years ago, the second crossing event took place in North America, and the Colombian mammoth obtained 1 1% to 13% of the genome from the real mammoth. By 65438+2000 years ago, when the Colombian mammoths were extinct, about three-fifths of their genomes came from real mammoths, and the other two-fifths could be traced back to the mysterious Mammoth Christoph. We can only know this mammoth from the DNA on one tooth.

This study also shows how early mammoths adapted to the cold. In the previous study of ancient DNA, scientists have deeply discussed the genetic details of the reproduction of true mammoths in low temperature environment. But many genetic variations behind the cold tolerance of real mammoths first appeared in early mammoths. The new research found that as early as 6.5438+0 million years ago, more than 85% of the variation of the true mammoth had already existed in the ancestor's cousin, the Siberian grassland mammoth.

According to fossil evidence, mammoths lived in high latitudes 6.5438+0 million years ago, so it is not surprising that these behemoths adapted to the cold climate. However, this study provides a unique perspective to observe their adaptation process. Mammoths seem to have evolved genetic mutations to adapt to the cold climate at a steady rate, not overnight.

Details in DNA

Paleontologists say that the discovery that Colombian mammoths are hybrids will prompt scientists to further re-evaluate the fossil record of North American mammoths.

A recent study compared mammoth tooth fossils with gene genealogy and found that the teeth of different mammoths are not exactly the same; Throughout North America, the shape and arrangement of mammoth teeth in different regions overlap to a great extent. New research also emphasizes this point: About 500,000 years ago, the tooth fossils of North American mammoths did not change much, although the genes of Colombian mammoths changed greatly.

"Without genetics, we usually look at changes in shape or shape; Without these shape changes, we can't record species changes, "said Lindsay Young, a paleontologist at Waco Mammoth National Reserve in Texas. "With genetic analysis, we can separate them and have data to support them."

Research co-author Adrian Lister is a paleontologist at the Natural History Museum in London and a world-leading expert on mammoth research. He believes that this study also highlights an unsolved problem: how to define the teeth of the North American mammoth without DNA. From a genetic point of view, if the Colombian mammoth only appeared 400,000 to 500,000 years ago, how do paleontologists define the identical and older mammoth teeth? So far, no one has published the DNA research on the teeth of North American mammoths more than 500 thousand years ago.

Dalén said that in order to solve more mysteries, he and his colleagues hope to apply record-breaking technology to the teeth of North American mammoths. The research team has identified the teeth of a mammoth in Canada 500,000 years ago and a real mammoth 200,000 years ago, which may be candidates for future sequencing.

Now, scientists have broken through the boundary of 65.438 billion years. As time goes by, scientists can uncover the secrets hidden in old DNA. "This is a very important question," Darren said. "According to the available data, I think it is relatively easy to move forward to 2 million years if there are good specimens."

(Translator: Sky4)