A tiny toebone from a Neanderthal woman who lived around 50,000 years ago has shown that several branches of early humans interbred before a single group, Homo sapiens, rose to dominate.
The bone has provided the final piece to a project, launched in 2006 by European evolutionary anthropologist Svante Paabo, to use ancient DNA to trace the human odyssey.
In a study published in the journal Nature, a team reports that the bone adds hugely to genetic knowledge of our cousins, the Neanderthals, who died out around 30,000 years ago.
The scientists compared the genome against those of two other human groups who shared the planet at the same time.
They were the Denisovans, another mysterious sub-group whose remains have been found in Siberia; and Homo sapiens, as anatomically modern man is called.
The comparison points to interbreeding – “gene flow” in scientific parlance – among the three groups, although the extent is rather limited.
Between 1.5 and 2.1 per cent of the genomes of humans today can be attributed to Neanderthals, it found. The exceptions are Africans, who do not have a Neanderthal contribution.
“We don’t know if interbreeding took place once, where a group of Neanderthals got mixed in with modern humans and it didn’t happen again, or whether groups lived side by side, and there was interbreeding over a prolonged period,” said Montgomery Slatkin, a professor at the University of California at Berkeley.
Denisovans, too, left their mark on modern man. Previous studies found that around six per cent of the genomes of Australian aborigines, New Guineans and some Pacific Islanders came from this group.
The new analysis found that the genomes of ethnic Han Chinese and other mainland Asian populations, as well as of native Americans, contain about 0.2 per cent Denisovan genes.
The Neanderthals, in turn, contributed at least 0.5 per cent of their DNA to the Denisovans.
Both of these groups have an intriguing genetic past, the new study says.
Around five per cent of the Denisovans’ genome come from some ancient forerunner.
One bet is that it is Homo erectus, said Kay Pruefer, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the comparison.