DNA from dirt: Tracing ancient humans found in 'empty' caves
No bones? No problem! Scientists say that they have figured out a way to extract tiny traces of ancient human DNA from dirt in caves that lack skeletal remains.
The technique could be valuable for reconstructing human evolutionary history, according to the study published yesterday in the journal Science.
That is because fossilized bones, currently the main source of ancient DNA, are scarce 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, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who co-authored the study.
The researchers collected 85 sediment samples from seven caves in Europe and Russia that humans are known to have entered or even lived in between 14,000 and 550,000 years ago.
By refining 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.
The researchers found evidence of 12 mammal families, including extinct species such as woolly mammoth, woolly rhinoceros, cave bear and cave hyena.
By further enriching the samples for human-like DNA, however, the scientists were able to detect genetic traces of Denisovans a mysterious lineage of ancient humans first discovered in a cave in Siberia - and Neanderthals from samples taken at four sites.
Crucially, one of the sites where they discovered Neanderthal DNA was a cave in Belgium, known as Trou Al'Wesse, where no human bones had ever been found, though stone artefacts and animal bones with cut marks strongly suggested people had visited it.
Eske Willerslev, who helped pioneer the search for DNA in sediment but wasn't involved in the latest research, said that the new study was an interesting step but cautioned that it is difficult to determine how old sediment samples found in caves are.