Neanderthals and humans interbred in Europe for 5,400 years Oct 24, 2014 3:37:09 GMT
Post by Admin on Oct 24, 2014 3:37:09 GMT
When humans hooked up with Neanderthals, we could have wooed them with music and fancy jewellery. The oldest DNA of a modern human ever to be sequenced shows that the Homo sapiens who interbred with the Neanderthals were very modern – not just anatomically but with modern behaviour including painting, modern tools, music and jewellery. Some previous estimates had placed the first interspecies liaison much earlier, before the emergence of these features. The new DNA sequence shows it actually happened in the middle of an age called the Initial Upper Palaeolithic, when there was an explosion of modern human culture.
About 2 per cent of many people's genomes today is made up of Neanderthal DNA, a result of interbreeding between the two species that can be seen in everyone except people from sub-Saharan Africa. The so-called Ust'-Ishim man, named after the town in western Siberia where he was found, carries a similar proportion of Neanderthal DNA in his genome as present-day Eurasians, and a combination of radiocarbon and genetic dating shows he died only about 45,000 years ago.
Geographic location, morphology and dating.
Before now we couldn't rule out that our fraction of Neanderthal ancestry was the result of interbreeding between Neanderthals and modern humans who were in the near east before Neanderthals got there, says David Reich from Harvard University, a co-author on the paper. While these near-eastern humans were anatomically modern, they did not show modern behaviour, he says.
The researchers could work out when Neanderthals first became part of the man's ancestry by analysing the lengths of the Neanderthal regions of DNA in his genome. DNA gets chopped up and scrambled over successive generations, and the lengths in his genome showed that he was descended a mere 230 to 400 generations from human-Neanderthal interbreeding between 7000 and 13,000 years before. This pinpoints the date of our interbreeding with Neanderthals to 50,000 to 60,000 thousand years ago, ruling out almost 50,000 years of previously possible dates.
Principal Components (PC) analysis exploring the relationship of Ust’-Ishim to present-day humans.
"This new paper definitively says it was modern humans with modern human behaviour that interbred with Neanderthals," Reich says. "The new timing rules out earlier modern humans in the Middle East [from participating] in the admixture," says Janet Kelso from the Max Planck Institute in Leipzig, Germany, one of the lead researchers on the project.
The Initial Upper Palaeolithic was a period around 50,000 years ago when complex stone and bone tools appeared across Eurasia, along with body ornamentation like pierced shells and animal teeth, pigments and even musical instruments, says team member Tom Higham of the University of Oxford. It is unknown which human-like species made these sophisticated artefacts, but the finding that Ust'-Ishim man was in Siberia at this time means that it could have been modern humans, he says.
Statistics testing whether the Ust’-Ishim genome shares more derived alleles with one or the other of two modern human genomes (X, Y).
At around 45,000 years old, Ust'-Ishim man is the oldest modern human ever to have been sequenced. This title was previously held by a a 24,000 year old boy, also from Siberia, whose DNA was sequenced last year. "This is very exciting research that shows again the remarkable power of ancient DNA analysis to help solve seemingly intractable questions in human evolution science," says Darren Curnoe from the University of New South Wales in Sydney, Australia.
By comparing Ust'-Ishim's genome to various groups of modern and ancient humans, the researchers are filling in gaps in the map of initial human migrations around the globe. They found that he is as genetically similar to present-day East Asians as to ancient genomes found in Western Europe and Siberia, suggesting that the population he was part of split from the ancestors of both Europeans and East Asians, prior to their divergence from each other.
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"He represents a group that settled Siberia and then disappeared without leaving descendants," says Curnoe. "This tells us that as early humans left Africa and settled Eurasia they weren't all successful. There were more populations than we thought, some making no contribution to living people at all." He notes this could make it difficult to interpret human fossils found in Eurasia, since we cannot assume that they are our ancestors.
But while Ust'-Ishim man does not appear to have any modern-day direct descendants living today, he is more genetically similar to present-day East Asians than to present-day Europeans. This finding is consistent with a recently proposed theory that present-day Europeans may have got some of their ancestry from later groups that weren't part of the initial migration into the area. "It supports that very strongly," says Reich, one of the researchers who developed the idea.
Crossroads for humanity: the river Irtysh in Western Siberia where the bone was found. It comes from a time when the human race was about to embark on its journey to the rest of the world
Analysing the lengths of Ust'-Ishim's Neanderthal DNA has pinpointed the early shared interbreeding event to around 230 to 400 generations before him, but some longer stretches of DNA indicate that his ancestors had also interbred with Neanderthals even more recently. "There may have been a later admixture event into the ancestors of this individual," says Kelso.
Because there are only a few of these longer stretches, they were unable to precisely date when this later interbreeding may have happened. But whatever the date, it seems humans and Neanderthals found each other irresistible, or at least mated with each other fairly commonly, whenever we inhabited the same areas. "The timing is most likely simply a result of the fact that this is where the two groups overlapped geographically and temporally," says Kelso.
Journal reference: Nature, DOI: 10.1038/nature13810