Sun. Feb 5th, 2023
Neanderthals and Denisovans probably also enjoyed the view from Denisova Cave.
Enlarge / Neanderthals and Denisovans probably also enjoyed the view from Denisova Cave.

Humans, modern and otherwise, have lived in Siberia’s Denisova Cave for tens of thousands of years, leaving behind a wealth of archaeological artifacts. The cave is known for giving its name to Denisovans, a type of human closely related to the Neanderthals. But Neanderthals also lived there.

In the main gallery of the cave, stone tools were left behind by people who lived thousands of years ago. Those people were probably Neanderthals, according to a newspaper in Science this week: The ground says so. While no Neanderthal bones have been found with the tools, the paper’s authors are the first to be able to detect the presence of humans based on DNA found in the soil. This allows them to paint a much more detailed picture of the past, in Denisova Cave and elsewhere.

“This is a game changer for researchers studying our hominid past,” said Christian Hoggard, an archaeologist at Aarhus University who was not involved in the story. His words are echoed by countless researchers who excitedly tweet the paper, “This is fucking unbelievable,” says Rob Scott, an evolutionary anthropologist at Rutgers. Tom Higham, an Oxford professor who specializes in bone dating, called the discovery a “new era in Paleolithic archaeology.”

Fishing for DNA

The rarity of ancient bones has always been a major obstacle for archaeologists. Ancient tools are a little less rare, but without bones it can be very difficult to work out which group of people were responsible for making them. That’s why detecting the presence of boneless people is so important to the field.

Viviane Slon, a researcher at the Max Planck Institute for Evolutionary Anthropology, worked with a large team of colleagues to extract genetic material from sediment samples in four caves in Europe. They focused on mitochondrial DNA, which is genetic material separated from a cell’s main DNA. “Mitochondrial DNA evolves faster… and is present in more copies per cell,” Slon told Ars. “So that would give us more opportunities to extract it from the sediment and also a better way to differentiate between different ones [species].”

How do you find out if there is Neanderthal mitochondrial DNA in the floor of an ancient cave? You take the soil—a tiny bit, Slon says, just half a teaspoon or so—and use chemical reagents to dissolve the genetic material. Once it’s in this form, you can extract DNA that can be read by a sequencing machine.

Slon and her colleagues were the first to capture mitochondrial DNA using a particularly clever extraction method. DNA works a bit like a zipper combined with a jigsaw puzzle, where each tooth on the zipper can only fit together with another tooth of a certain species. Because we already have data on a number of different ancient species, it’s possible to create some kind of genetic bait for DNA sequences by synthesizing half of the zipper. Once the bait is placed in the solution, the other half of the zip tie is attached to it and can be removed.

Neanderthals and mammoths and rhinoceroses, oh my

Using this technique, Slon and her colleagues found the DNA of ancient mammals such as woolly mammoths and woolly rhinoceroses, as well as DNA from Neanderthals and Denisovans. They checked for contamination by modern genetic material by looking at the damage that occurs in ancient DNA. They also made sure to identify exactly which mammal species were identified by the DNA. They wanted to make sure that the DNA actually belonged to ancient species.

The researchers also checked whether their results matched the existing archaeological record. In three different caves, they found Neanderthal DNA in places where Neanderthal bones had previously been found, exactly where you’d expect it.

These signs that the method was working reliably meant the researchers could move on to locations whose previous inhabitants were unknown. That included the discovery of Neanderthal DNA with the tools in Denisova Cave. Neanderthal DNA also turned up at Trou Al’Wesse in Belgium, where tools and animal bones suggest the presence of Neanderthals, but no Neanderthal bones have ever been found.

“It’s a really well done study,” said Mikkel Winther Pedersen, a researcher who specializes in ancient DNA who was not involved in the paper. They build on a solid body of existing research on these methods, he says, and the results are important for archeology — not just because of the findings, but because it means it’s possible to actually use “whatever the archaeologists usually throw at random.” “. gone: the dirt. Save the Dirt!”

Hoggard agrees, saying the research will likely change how researchers approach archaeological sites. Researchers may be more inclined to choose sites with good sediments rather than just good artifacts, he told Ars, and “We will be more inclined to analyze the sediments and preserve them in a different way than before.” There is also likely to be increased awareness of contagion.

The new method described in Science doesn’t mean the past is now an open book — the oldest sequence analyzed so far is about 700,000 years old, Slon says, and it’s particularly well preserved because of the low temperatures. Older sequences can still be recovered, but at present it is not feasible that DNA evidence can be used to answer questions about early Homo kind. Also, DNA can leak from one layer in a cave to another, making the results difficult to interpret.

The next step, Slon says, will be to look at the archaeological sites that have stone tools but no clear evidence of who made them. “We could extract DNA from the sediments to determine which hominin groups were present,” she says. Hoggard thinks it would be a fascinating avenue to see “if we can detect Neanderthal DNA in sites known to contain modern humans.” Or, he adds, this method could answer questions about another story in the news this week, the hints of people in the Americas 130,000 years ago.

Science2016. DOI: 10.1126/science.aam9695 (About DOIs).

By akfire1

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