Deep in the Altai Mountains of Siberia lies a cave filled with unimaginable treasure, not silver or gold but genetic treasure that reveals the complex and fascinating story of our species, and that of other humans we once shared our planet with. The significance of this cave is immense, and its discovery has helped shine a light on the murky world of ancient humans and their closest relatives.
It began with a discovery in 2008 of a bone fragment from the finger of what turned out to be a teenage girl from an unknown human species, later named “Denisovans” after the cave in which these fragments were found. In 2010, a molar from a young adult was found that also turned out to be from the same archaic hominin and, in 2011, a toe bone contemporary with the finger bone was discovered that contained mitochondrial DNA from a Neanderthal and not a Denisovan.
Tools from modern humans have also been discovered in the cave, so clearly there is enough data to suggest that numerous hominins sought shelter in the cave at one time or another. Altogether, more than 80,000 exhibits that include tools, ornaments, and the remains of animals and plants have been found.
The latest genetic treasure came in the form of DNA extracted from bone fragments discovered in 2016. The results show the subject to be a young girl with mixed parentage; she was the offspring of a Neanderthal mother and a Denisovan father. The discovery, reported in Nature reveals a rare insight into the lives of our closest archaic human relatives.
“We knew from previous studies that Neanderthals and Denisovans must have occasionally had children together, but I never thought we would be so lucky as to find an actual offspring of the two groups,” says Viviane Slon, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Modern humans retain DNA fragments from both Neanderthals and Denisovans, and in some cases, genetic remnants from as yet unidentified archaic hominins.
The young girl is estimated to be around 13 years old and researchers deduced that her mother was genetically closer to Neanderthals who lived in western Europe than to the Neanderthals who lived earlier in the Denisova Cave. The father was shown to be more closely related to Denisovans that later inhabited the cave, but curiously also showed evidence of some distant Neanderthal ancestry. This suggests that Neanderthals migrated between Western and Eastern Europe before they died out.
“The cool thing about this is, this is extremely direct evidence,” says Svante Paabo, a molecular geneticist who led the new research. “The finding of a first-generation Neanderthal-Denisovan offspring amongst such a small number of archaic specimens sequenced to date suggests that mixing between Late Pleistocene hominin groups was common when they met.”
The idea that various groups of ancient humans interbred suggests that encounters between these hominins may not have been as violent as once suspected. The arrival of modern humans from Africa, later on, may have resulted in a melting pot where Neanderthals and Denisovans were simply absorbed into the Homo sapiens gene pool. A relatively peaceful co-existence seems likely, thanks to interbreeding.
The DNA of some Australasians, in particular, those from Papua New Guinea, is about 5% Denisovan whilst non-Africans carry an average of 2% Neanderthal DNA. It is estimated that at least half of the entire Neanderthal genome is alive and well in Eurasians today.
Elsewhere, evidence of archaic admixture from an unknown hominin has been discovered in the genome of the Yoruba in Nigeria and Melanesians in the Pacific Ocean. More data is almost certainly waiting to be found, and the story of the numerous species of humans that once inhabited our planet still has plenty of surprises in store. The ability to sequence archaic homo DNA is now the most exciting and powerful tool in our quest to understand human origins.