Humans also interbred with the Denisovans, a group known only from a pinky finger bone and a few teeth recovered from a Siberian cave, dating to about 100,000 years ago. (Neanderthal and Homo sapien remains have also been found in the cave.) Most of what we know of the Denisovans comes from the ancient DNA gleaned from these remains. Modern Aboriginal Australians and Melanesians have the highest percentage of Denisovan DNA in their genome (2-4%), while modern Tibetans are likely to have inherited their ability to cope with high altitudes from Denisovan ancestors.
All this suggests that Denisovans could have lived throughout Asia. Indeed, 10,000 to 14,000 year-old fossils from caves in southwest China – the Red Deer Cave and Longlin people – may even turn out to be Denisovan.
These stone-age cave dwellers are believed to have borne traits similar to modern humans, as well as more archaic features. “We don’t quite know fully what we’re dealing with,” says Darren Curnoe, from the University of New South Wales. A small femur from Longlin, for instance, is more reminiscent of Homo erectus than modern Homo sapiens, he says, and could hint at Homo erectus having survived and spawned descendants in Asia much later than once thought.
The Denisovans weren’t a picky lot. In addition to mating with humans, their DNA also bears the hallmarks of interbreeding with Neanderthals and a more archaic mystery species. Some speculate that this could be Homo erectus, or
Homo floresiensis, but until efforts to extract DNA from these species is successful we won’t know for sure.
‘I’D HAVE LOVED to have been on the planet 60,000 years ago,” says archaeological scientist Richard “Bert” Roberts, from the University of Wollongong, who helped date the Hobbit remains. “We used to have a fabulous time, with all sorts of other humans running around the planet.”
However many times we and our extinct relatives did interbreed, these ancient DNA studies highlight how different modern times are to almost any other period in our pre-history. We roam the world now as the single living representative of the Homo line, all previous times have seen the world populated by multiple related – and often intermingling – species. Our once bushy family tree has been pruned back to a lone twig.