When studying ancient DNA, researchers typically use teeth or bones found in fossils. However, while fossils are useful, they only include a snapshot of an individual's DNA within a genus, not the genetics of the whole population, according to Caroline Delbert of Popular Mechanics.
A research team has sequenced the complete genomes of two ancient bears using only urine and feces contained in soil samples from the Chiquihuite Cave in Northern Mexico, which is a "science first." The discovery demonstrates that near-complete genomes and high-quality DNA can be reconstructed and analyzed without fossils. According to Elizabeth Pennisi of Science, researchers used the tool to piece together the origins of North American Stone Age bears. The research was published in Current Biology this month.
The study's researchers previously discovered stone tools and fragments dated to 25,000 and 30,000 years in Chiquihuite Cave in 2012, according to Science. The tools revealed that people once lived in the cave, so the team took samples of soil from the floor to see what else could have lived there years before. A total of 48 samples of soil were recovered and sequenced, according to Science.
According to Michelle Star of Science Alert, researchers discovered urine droplets and feces from Upper Paleolithic bears that used the Chiquihuite Cave as a shelter-and toilet-16,000 years ago in soil samples. The researchers sequenced the complete genomes of two ancient bears using excrement. Most of the bears were the forerunner of the American black bear, which can still be seen today. According to Science Alert, the other genome matched a now-extinct mammal, the big short-faced bear, which went extinct 11,000 years ago.
"Cells from the body are excreted as an animal, or a human urinates or defecates. And it is the DNA fragments from these cells that we will use in soil samples. For the first time, we reconstructed genomes - genetic profiles - based on these fragments using incredibly efficient sequencing techniques. "In a statement, Eske Willerslev, a geneticist at the University of Copenhagen in Denmark, summarized the findings.
Extinct Bear Waste
According to Popular Mechanics, the researchers used eight contemporary Ursidae bears and three extinct bears as a guide to completely sequence the ancient bears' genomes. The researchers pieced together how black bears populated and spread across North America when the Ice Age ended using the recently reconstructed ancient bear genome, according to Science.
They did so by comparing ancient genome sequences from 83 modern-day black bears in North America and three short-faced bears who lived about 22,000 years ago in Canada, according to Science Alert. According to Science, some black bears migrated north as far as Alaska, while others migrated west, where their descendants settled the southwestern United States. Although scientists aren't sure exactly when the bears started to expand into ice-free areas, they do know that it was about 12,000 years ago when the planet began to warm up.
Purpose of the Study
Aside from presenting new information about black bear origins, the new study demonstrates how scientists can now patch together genomes using environmental DNA rather than fossils to better understand how a population originated, according to Science Alert.
"Analysis of DNA contained in soil has the potential to extend the narrative on everything from species evolution to climate change developments-this is the Moon landing in genomics because fossils will no longer be needed," said Willerslev in a statement.
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