London: Scientists have found that a 30,000-year-old bone finger fossil of a little girl found in Siberia in 2008, was neither a Neanderthal nor an early modern human, but from a third group of humans which wasn’t known until now.
The team from the University of California, Santa Cruz, analysed the DNA and extracted a genome sequence, which has revealed an extinct branch of the human family tree, called ‘Denisovans’.
They compared the sequence with those of Neanderthals and modern humans to determine that the Denisovans were a sister group to the Neanderthals, descended from the same ancestral population that had separated earlier from the ancestors of present-day humans.
The study also found surprising evidence of Denisovan gene sequences in modern-day Melanesians.
"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,” said Richard Green.
The Denisovans appear to have been quite different both genetically and morphologically from Neanderthals and modern humans.
According to Green, there was probably an ancestral group that left Africa between 300,000 and 400,000 years ago and quickly diverged, with one branch becoming the Neanderthals who spread into Europe and the other branch moving east and becoming Denisovans.
When modern humans left Africa about 70,000 to 80,000 years ago, they first encountered the Neanderthals, an interaction that left traces of Neanderthal DNA scattered through the genomes of all non-Africans. One group of humans later came in contact with Denisovans, leaving traces of Denisovan DNA in the genomes of humans who settled in Melanesia.
"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," Green said.
"And you have to wonder if there were other populations that remain to be discovered. Is there a fourth player in this story?"
The findings are reported in the December 23 issue of Nature.