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Climate Link To Neanderthal Demise Abates

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By Rick Weiss
Washington Post Staff Writer
Thursday, September 13, 2007

The case isn't closed yet, but modern humans are looking awfully guilty in one of the biggest whodunits in prehistory: the case of the demise of the Neanderthals.

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So say scientists who have measured with unprecedented precision what the climate was like when humankind's closest relatives went extinct about 30,000 years ago.

Contrary to a popular hypothesis that Neanderthals succumbed to a suddenly colder climate, the new research indicates that southwestern Europe, where our beetle-browed cousins made their last stand, enjoyed relatively mild weather when their last campfires went cold.

"We found there was a lot of rain but no major change in climate," said Chronis Tzedakis of the University of Leeds, a leader of the study published in today's issue of the journal Nature. "It is hardly something we can invoke to explain their demise."

That pretty much leaves one suspect: the butler -- or more precisely the predecessors to all butlers and to modern humans, generally, who were making their initial sweep across Europe at the time.

Neanderthals were widespread in Europe for more than 100,000 years but went extinct 26,000 to 32,000 years ago. Some scientists have blamed climate, which was then undergoing wild fluctuations between thousand-year cold spells and warmer periods, separated by as little as a decade or two. A few of those cold spells were extreme, leading some scientists to suggest that one of those mini-ice ages finally did in the climate-stressed Neanderthals.

Others have placed the blame on the ancestors of modern humans, who emerged from Africa about 40,000 years ago and then spread north and west through Europe.

Although it would fall short of absolute proof, evidence that the Neanderthals disappeared just when a major cold snap hit would potentially exonerate modern humans. Until now, however, scientists have been unable to tell with sufficient resolution when, exactly, the warmer and colder spells occurred.

That's because the primary means of dating prehistoric materials and events -- measuring atomically unstable carbon 14 in ocean sediments and ice cores -- can err by several thousand years when used on samples more than 20,000 years old.

The new work relies on a unique resource: a nearly 50-foot-long, oxygen-depleted sample of marine sediment drilled from Venezuela's Cariaco Basin. Studies by Konrad Hughen of the Woods Hole Oceanographic Institution in Massachusetts have shown that layers of that core -- undisturbed for millennia because the lack of oxygen kept worms and bugs from reaching them -- can tell with uncanny resolution what the climate was like in the Northern Hemisphere.

Hughen, Tzedakis and colleagues used the core to determine the climate in Gibraltar, where the most recent remnants of Neanderthal culture have been found. They focused on three time periods: 28,000 and 32,000 years ago (when, according to the best evidence, Neanderthals died out) and 24,000 years ago (when, according to one controversial estimate, the last Neanderthals died).

Climate was moderate during all three of those periods, they found, with extreme cold not arriving until about 21,000 years ago.

"I find the work both novel and solid," said Jan Heinemeier, a physicist who does carbon dating at the University of Aarhus, Denmark.

A gradual cooling of northern Europe may have played a role by pushing modern humans south, but from there either warfare or competition for resources must have been key, Hughen said.

"They survived 20,000 years of very unstable climate. Then when you add humans to the mix, they are gone within 10,000 years," Hughen said. "You tell me what the most parsimonious explanation is."


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