Scientists found DNA from ancient humans in the soil of caves — even when there were no bones uncovered at the site. The research shows that, even when no fossils are around, sediments inside caves can tell us which early humans were present where and when. This information is key for understanding the evolution of our human ancestors.
The study, published today in Science, describes a highly sensitive technique for analyzing ancient DNA. The technique was used to study sediment from seven caves in Europe and Russia, dating between about 14,000 and 550,000 years ago. Among countless genetic fragments, the researchers were able to detect the DNA of Neanderthals and Denisovans, even when no bones were around.
"This approach is really the first to look specifically for human and hominin DNA directly in sediments. I think this is the novelty," says Beth Shapiro, a professor of ecology and evolutionary biology at UCSC, who did not take part in the study. "It opens up new possibilities for research in archaeology."
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To date, our understanding of how early humans, collectively called hominins, evolved is mostly based on the few fossils we have found scattered around the world. The skeletal remains are rare — sometimes there are just teeth or a pinky toe fragment — and so they provide a very limited picture of where and when our human ancestors lived. Our extinct kin include Neanderthals, who lived between about 400,000 to 40,000 years ago in Europe and parts of Asia; and Denisovans, who split off from Neanderthals some 380,000 years ago. Both were eventually replaced by Homo sapiens.
Scientists have long known that soil in caves is filled with valuable DNA. But ancient DNA is very fragmented, and until recently, the technology didn't really allow us to analyze this damaged genetic material and get very accurate results. The group that worked on today's study — including author Matthias Meyer at the Max Planck Institute for Evolutionary Anthropology — have been at the forefront of recovering ancient DNA from poorly preserved specimens, Shapiro tells The Verge. Meyer is "one of the most creative people when it comes to thinking about methods for recovering ancient DNA," she says.
The technique described in the study was able to identify genetic material that belonged to hominins as well as a variety of animals such as the woolly mammoth and woolly rhino, both of which are extinct. "This is really a great study that kind of returns to this earlier question that was out of reach for so long, applying all these new methods," says Christina Warinner, an assistant professor of anthropology at the University of Oklahoma, who did not take part in the study. "It's really exciting."