Neanderthals died out earlier than previously thought
24 May 2011, by Tamera Jones
Neanderthals may have died out 10,000 years earlier than previously thought, and possibly not long after they encountered modern humans, a new study suggests.
An international team of scientists used an improved technique to more accurately date fossils and found that Neanderthals died out close to 39,000 years ago, not 29,000 years ago, as suggested by previous estimates.
Modern humans are thought to have first appeared around the Caucasus region – where Europe and Asia meet – around 44,000 years ago, which means that modern humans and Neanderthals may have co-existed for a few thousand years.
'A short period of contact between modern humans and Neanderthals points to the likelihood that Neanderthals went extinct when humans arrived in the Caucasus. Or they may already have become extinct by the time humans arrived in the region,' says Dr Thomas Higham from the University of Oxford, one of the co-authors of the study, published in Proceedings of the National Academy of Sciences.
A key question for researchers, which so far has no clear-cut answer, is whether or not Neanderthals and modern humans ever bred when they came into contact around the Caucasus.
Last year, a study published in Science found that around one to four per cent of our genes are derived from Neanderthals, which suggests that we may have bred with them at some point in the distant past. This was a huge surprise at the time, because many researchers had thought that as soon as modern humans came across Neanderthals, Neanderthals failed to compete, so soon died out – the assumption being that the two didn't interbreed.
'The only way to resolve this issue is to date the fossils more accurately,' says Higham.
'We think the extinction of Neanderthals at this time is an indicator of when modern humans moved into the area.'
Dr Thomas Higham, University of Oxford
So Higham and colleagues from University College Cork and the Laboratory of Prehistory decided to do just that. They analysed fragments of Neanderthal bone and collagen from Mezmaiskaya Cave in Russia using an ultra-filtration technique, which takes out impurities, allowing them to pin down a more accurate date than was previously possible.
Mesmaiskaya Cave is in a region which is thought to be a crossroads for the movement of modern humans into the Russian plains.
A previous study had dated a bone sample from a deeper layer in the cave to 29,000 years old. The sample that Higham and his colleagues analysed came from a shallower layer, so in theory it should have been younger than 29,000 years old. But in fact, they found that their sample dated back to 39,000 years.
Older dating techniques are prone to error, because contaminants from more modern times find their way into ancient samples, leading to a younger final date.
'Less reliable dating techniques appear to often underestimate the true date of bone and collagen fossils by several thousands of years,' says Higham.
The method perfected by Higham and a team of scientists from the University of Oxford removes this uncertainty by cleaning up the sample more effectively using ultra-filtration.
Using the new technique, Higham has dated several samples from the Mezmaiskaya site and found that none are younger than 39,000 years old.
Now the new findings means it's less likely that Neanderthals and modern humans bred in the Caucasus region, but instead hooked up a long time before then in the Middle East, and might explain why we've inherited only a tiny percentage of their DNA in our genome.
'We think the extinction of Neanderthals at this time is an indicator of when modern humans moved into the area,' Higham says.
Ron Pinhasi, Thomas F. G. Higham, Liubov V. Golovanova, and Vladimir B. Doronichev, Revised age of late Neanderthal occupation and the end of the Middle Paleolithic in the northern Caucasus, Proceedings of the National Academy of Sciences, Published online before print May 9, 2011, doi: 10.1073/pnas.1018938108
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