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Neanderthal extinction earlier than thought


Archaeological material can appear younger than it is if the samples being dated are contaminated with more recent material (Source: absolutely_frenchy/La Grotte de Clamouse/iStockphoto)


Over the past 20 years, it has become widely accepted that the Iberian peninsula - modern day Spain and Portugal - served as a kind of refuge for the last remaining Neanderthals, who survived there five or ten thousand years longer than they did elsewhere in Europe.

Much of the evidence for this hypothesis came from radiocarbon dating of material found in caves associated with Neanderthal fossils or the particular kinds of stone tools, known to archaeologists as Mousterian, which are closely associated with the species.

North of the Ebro valley which crosses northern Spain, scientists previously found that evidence of Neanderthals disappeared around 42,000 years ago when anatomically modern humans arrived. South of that valley, it appeared, Neanderthals survived until 36,000 years ago with little evidence of modern humans.

"People have suggested that in the south of Iberia we've got Neanderthals' surviving for five or ten thousand years beyond anywhere else in Europe, and we don't have modern humans in that area," explains Dr Rachel Wood, from the Australian National University. Her group's new analysis of the story appears in the current issue of the Proceedings of the National Academy fo Sciences.

However Wood and her colleagues had doubts about the accepted version of events for two reasons.

"In hot environments, the organic materials, like bone and charcoal, we want to date is poorly preserved, so southern Spain is the area in Europe where we would expect our samples to be the least well preserved," she explains.

"Added to that, if you add just a little bit of young carbon to an old sample, the error on your radiocarbon date will be really big. If you add one percent modern carbon to a sample that is 60,000 years old you'll measure an age of 37,000."

"So the divide in Iberia, with a prolonged survival of Neanderthals to the south, is exactly the pattern you'd expect if the radiocarbon dates associated with those final Neanderthals are incorrect [due to the sampling errors]."

Older and older

In an attempt to eliminate younger carbon that may have skewed the dating in earlier studies, Wood and her colleagues used ultrafiltration to purify bone collagen from two key sites in Spain, known as Jarama VI and Zafarraya.

This process produced ages at least 10,000 years older than previous attempts, Wood says.

"When we re-date these sites with a better method they become older and older."

The two key sites she and her colleagues tested "are now completely removed from the 'late' period - less than 42,000 years. They're definitely not late Neanderthal," she says.

Extrapolating further, the researchers say that all of the radiocarbon dates from the region may be inaccurate and need testing.

The results seem to send archaeologists back to the drawing board to try and understand what happened south of the Ebro Valley during the Middle and Upper Palaeolithic.

"What we're left with is a gap [in archaeological evidence], where we haven't really got anything at all," says Wood.

"For the moment, I think we need to move away from this assumption that we have these late Neanderthals in the south of Iberia and all the implications that has for interactions with modern humans in the rest of Europe."

Tags: archaeology