DNA taken from the 30,000 year old finger bone of a young girl was found to be neither from early human nor Neanderthal, and was from a previously unknown species, now called Denisovan.
The bone, along with a tooth fragment, was discovered in the Denisova cave in southern Siberia, and its DNA was found to be distinct from human or Neanderthal.
Researchers say that like Neanderthals, Denisovans interbred with early humans, and traces of their DNA can be found in modern day Melanesians–those from the islands around Papua New Guinea.
Scientists say they would have inhabited land across Asia, only to become extinct alongside the Neanderthals as early humans thrived.
The bone was found in 2008 by Russians, and examined by a team led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
They compared the Denisovan genome sequence to the recently unravelled Neanderthal genome, as well as to modern humans.
Denisovans were found to be a sister group to Neanderthals, and had descended from the same ancestors who split from the ancestors of modern humans.
Scientists had known that Neanderthals and early humans had interbred, as there is Neanderthal DNA in all non-African humans.
But they found that Denisovans also interbred with humans–and traces of their genes are found in modern-day Melanesians, suggesting the cavemen travelled widely across Asia, reports Nature.
Professor Richard Green of the University of California, Santa Cruz, said: “The story now gets a bit more complicated.
“Instead of the clean story we used to have of modern humans migrating out of Africa and replacing Neanderthals, we now see these very intertwined story lines with more players and more interactions than we knew of before.
“It was fortuitous that this discovery came quickly on the heels of the Neanderthal genome, because we already had the team assembled and ready to do another similar analysis.
“This is an incredibly well-preserved sample, so it was a joy to work with data this nice.
“We don’t know all the reasons why, but it is almost miraculous how well-preserved the DNA is.”
He said that the Denisovans were “quite different both genetically and morphologically from Neanderthals and modern humans”, with the tooth similar to those of much older human ancestors, such as homo erectus.
It was unclear why the species had not been discovered before–but Prof Green said that because both the bone and the tooth, which came from different members of the same population, resembled those of earlier humans other finds may have been overlooked.
He said: “It could be that other samples are misclassified.
“But now, by analysing DNA, we can say more definitively what they are.
“It’s getting easier technically to do this, and it’s a great new way to extract information from fossil remains.”
Prof Green said the evidence now suggests that an ancestral group of early humans left Africa up to 400,000 years ago and diverged, with one branch heading to Europe and becoming the Neanderthals and a second moving east and becoming Denisovans.
When modern humans left Africa–some 80,000 years ago–they came into contact with first the Neanderthals before another group interbred with Denisovans, the traces of which now exist in Melanesia.
Prof Green said: “This study fills in some of the details, but we would like to know much more about the Denisovans and their interactions with human populations.
“And you have to wonder if there were other populations that remain to be discovered. Is there a fourth player in this story?”
The bone, along with a tooth fragment, was discovered in the Denisova cave in southern Siberia