Cape Town - The thigh bone of a man who died in western Siberia about 45 000 years ago has yielded secrets about our Stone Age ancestry – particularly about the intermixing between early modern humans and Neanderthals.
The fairly complete bone was found in 2008 on a river bank near Ust’-Ishim and radio-carbon dated to about 45 000 years old.
Now a team of researchers, led by Svante Pääbo, Bence Viola and Janet Kelso of the Max Planck Institute – with the participation of UCT archaeology researcher Domingo Carlos Salazar Garcià – have sequenced the genome of the Siberian man, the earliest human to have been sequenced.
They found he was more closely related to people living outside Africa than to Africans, showing he was an early representative of the modern human population who migrated from Africa.
When his genome was compared with those of people living outside Africa, it was found he was about equally related to people living in east Asia and Europe during the Stone Age.
Because he lived at a time when Neanderthals were still living in Europe and Asia, the researchers were curious to see whether his ancestors had mixed with Neanderthals.
What they found was that about two percent of his DNA came from Neanderthals, which is about the same amount of Neanderthal DNA found in Europeans and east Asians alive today.
But what was different was the length of the Neanderthal DNA segments, which were much longer in the Siberian man than in present-day humans. This was because he lived much closer in time to the interbreeding between early modern humans and Neanderthals – the Neanderthal segments had not had time to become smaller.
Based on the length of the genomic segments of Neanderthal ancestry, the researchers estimated that the interbreeding with Neanderthals had occurred with the ancestors of the Siberian man between 7 000 and 10 000 years before he was alive.
That would put the interbreeding between modern humans and Neanderthals at between 50 000 and 60 000 years ago – which coincided with the expansion of modern humans out of Africa.
Previous estimates ranged from 37 000 to 86 000 years ago.
Alan Morris, from UCT’s human biology department in the medical school, said what he found particularly interesting was that Neanderthals were around at the time the Siberian man was alive, but that there appeared to be no further mixing between the two groups.
“To me that suggests two things: either Neanderthals were so rare 45 000 years ago that his group was not meeting them, or they were still within sight of each other, but they were no longer interbreeding, that something prevented their admixtures,” Morris said.
Cape Times