Researchers often look for ancient bones and teeth in a bid to learn more about extinct human relatives, but for the first time, scientists were able to detect DNA from the Neanderthals and the Denisovans in ancient muds in caves even without the skeletal remains of these individuals.
Alternative Method Of Gathering Information About Extinct Human Relatives
The work suggests it is possible for scientist to detect the DNA of extinct human lineages in places with no skeletal remains. If verified, the technique they used may help fill the gap on current understanding of the evolution of humans given the difficulty in finding skeletal remains of extinct human relatives.
The mysterious Denisovans and the Neanderthals are believed to have a common ancestor that split from the lineage of modern humans about 765,000 years ago.
Since DNA binds to the mineral component of bones, geneticist Matthias Meyer, from Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues conducted an investigation to determine if the same could happen in ancient sediments full of minerals.
The researchers conducted an analysis of 85 samples of sediments hailing back from 14,000 to 550,000 years ago. The samples were collected from seven different sites where earlier research suggested ancient humans once lived. Included in these sites is the Denisova Cave, where the first fossils of the Denisovans were discovered.
The researchers used a special technique that looks for mitochondrial DNA of mammals. To ensure that they do not get modern genetic materials, Meyer and colleagues only analyzed the short sequences marked by chemical damage that typically characterize ancient DNA.
Researchers were able to identify DNA from a number of animals that include woolly mammoths and cave bears, but mixed in with these animal DNA were traces of human DNA. They found Neanderthal DNA in four caves and the Denisovan DNA in Siberia's Denisova Cave.
"Using targeted enrichment of mitochondrial DNA we show that cave sediments represent a rich source of ancient mammalian DNA that often includes traces of hominin DNA, even at sites and in layers where no hominin remains have been discovered," the researchers wrote in their study published in the journal Science on April 27.
"Our work opens the possibility to detect the presence of hominin groups at sites and in areas where no skeletal remains are found."
Problems With This Method
One problem about this technique is that DNA may seep across layers of sediments, so it is difficult to know the time when the extinct humans lived at a particular site. The exact sources of the DNA are not also clear. The DNA may have come from fecal matter, body fluids, hair, and bones, but researchers currently have no way of telling the exact source of the genomes.
"The technique could increase the sample size of the Neanderthal and Denisovan mitochondrial genomes, which until now were limited by the number of preserved remains. And it will probably be possible to even recover substantial parts of nuclear genomes", said Carles Lalueza-Fox, from the Institute of Evolutionary Biology.