For the first time, scientists have successfully sequenced ancient DNA from organic remains left over from Paleolithic bears on the floor of a cave in Mexico. About 16,000 years ago.
Scientists have classified the achievement as “The landing of genomics on the moon”, because it means that fossilized remains are no longer the only way to obtain ancient DNA. Moreover, it shows that ancient DNA can now be studied in the context of a population, rather than scattered and dispersed individuals.
When an animal or human urinates or urinates, the organism’s cells are also excreted. The DNA fragments of these cells are what we can discover in soil samples. “ Explained geneticist Eske Willerslev from the University of Copenhagen in Denmark.
“Using very powerful sequencing techniques, we reconstructed genomes (genetic profiles) based on these segments for the first time. We have shown that hair, urine and faeces provide genetic material that, under the right conditions, can survive more than 10,000 years. “ Added.
Chickoyhuit Cave, where samples were obtained, is known as a site of historical interest. Numerous stone tools and pieces, dating from between 25,000 and 30,000 years ago, show the period of human occupation. But humans were not the only ones to use the cave.
The bones and traces of DNA also revealed the presence of a variety of animals, including bears, bats, mice, rodents and kangaroo mice. Using these samples, Wellersleaf and his team have now sequenced and recreated the genomes of two Paleolithic bears.
The first specimen was the ancestor of the modern American black bear (Ursus americanus), which still roams the forests of the North American continent. The second is the now extinct gigantic short-faced bear (Arctodus simus), one of the largest bears ever found, which became extinct at the end of the last ice age about 11,000 years ago.
The researchers then compared these genomes with those of other bears, including 83 current black bears from the United States and Canada, and three short-faced giant bears that lived in the Yukon, Canada about 22,000 years ago, according to their analysis. Fossilized remains.
They found that Chiquihuite black bears are closely related to modern bears in North America, but also share ancestry with Alaskan black bears.. Researchers also discovered that Chiquihuite bears belong to the Eastern subspecies, and that this was the first to diverge from other current groups of American black bears.
The DNA of short-faced giant bears was assembled using DNA from all eight modern bears in the family of Ursidae, as well as the three extinct bears and the three short-faced giant bears in the Yukon Territory.
“It was clear that the short-faced bears that lived in northern Mexico were different from the bears [de cara corta] Living in northwest Canada “, Said geneticist Mikel Winter Pedersen from the University of Copenhagen.
“This is an excellent example of the new knowledge that suddenly becomes available when genomes are reconstructed based on DNA fragments extracted from the soil,” Added.
The researchers said that in addition to the bear discoveries, which fill in some gaps in our knowledge of animal ancestors in the Americas, the results show that we can now obtain more environmental DNA than was previously possible.
Only DNA fragments found in sediments are used to show the presence of a certain species at a certain place and time. Now, using the techniques mentioned above, scientists can learn more about these animals. For example, when they fit into their family tree, when they migrated and separated from their common ancestors.
Around the world, all scientifically involved in the study of ancient DNA have recognized the need to reconstruct genomes from fragments found in soil or sediments. Being able to do this for the first time means that we have opened new frontiers. ” Willersleaf said. .
“Analyzing DNA in soil could have the potential to broaden the narrative about everything from species evolution to developments in climate change; that’s the moon landing to genomics because fossils won’t be necessary anymore.”