DNA from dirt: Tracing ancient humans found in 'empty' caves
No bones? No problem!
Scientists say they've figured out a way to extract tiny traces of ancient human DNA. It comes from dirt in caves. Even from caves that lack skeletal remains.
The technique could be valuable. It could help to reconstruct human evolutionary history. This is according to a study. It was published in the journal Science.
That's because fossilized bones are scarce. They are currently the main source of ancient DNA. This is even at sites where circumstantial evidence points to a prehistoric human presence.
"There are many caves where stone tools are found but no bones," said Matthias Meyer. He is a geneticist. He is at the Max Planck Institute for Evolutionary Anthropology. It is in Leipzig, Germany. He co-authored the study.
The researchers collected 85 sediment samples. These came from seven caves in Europe and Russia. The caves are where humans are known to have entered or even lived in. This happened between 14,000 and 550,000 years ago.
The researchers refined a method previously used to find plant and animal DNA. They were able to search specifically for genetic material belonging to ancient humans and other mammals.
Scientists focused on mitochondrial DNA. It is passed down the maternal line. It is particularly suited to telling apart closely related species. By analyzing damaged molecules, they were able to separate ancient genetic material from any contamination left behind by modern visitors.
The researchers found evidence of 12 mammal families. They included extinct species such as woolly mammoth, woolly rhinoceros, cave bear and cave hyena.
By further enriching the samples for human-like DNA, the scientists were able to detect genetic traces of Denisovans and Neanderthals. The Denisovans are a mysterious lineage of ancient humans. They were first discovered in a cave in Siberia. Samples were taken from four sites.
One of the sites where they discovered Neanderthal DNA was a cave in Belgium. It is known as Trou Al'Wesse. No human bones had ever been found there. Stone artifacts and animal bones with cut marks strongly suggested people had visited it.
Eske Willerslev helped pioneer the search for DNA in sediment. He wasn't involved in the latest research.
Willerslev said the new study was an interesting step. But he added a caution. It's difficult to determine how old sediment samples found in caves are.
"In general (it) is very disturbed and unless you can show that's not the case you have no idea of the date of the findings," he said.
Willerslev is an evolutionary geneticist. He teaches at the University of Copenhagen. That is in Denmark.
Meyer said the new method greatly increases the number of sites where archaeologists will be able to find genetic evidence. This will help fill gaps in the history of human evolution and migration. That includes how widespread Neanderthal populations were. And, which stone tools they were able to make.
Scientists may also be able to greatly expand their limited knowledge of the Denisovans. Their DNA can still be found in Melanesians and Aboriginal Australians today, by using the new procedure.
"In principle, every cave where there's evidence of human activity now offers this possibility," Meyer told The Associated Press.
CRITICAL THINKING QUESTION
Why aren’t bones found everywhere?
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