BERLIN - Humans and Neanderthals may have coexisted in Europe for more than 5,000 years, providing ample time for the two species to meet and have sex, according to new research.
Pinpointing how and when the Neanderthals became extinct has been tough because the standard process of radiocarbon dating is unreliable for samples that are more than 30,000 years old, due to contamination.
The latest six-year project by researchers at the University of Oxford used modern methods to remove contaminants and accurately date nearly 200 samples of bone, charcoal and shell from 40 important archaeological sites across Europe.
Using the new techniques and mathematical models, researchers concluded with a high probability that pockets of Neanderthal culture survived until between 41,030 and 39,260 years ago.
Although this puts the disappearance of Neanderthals earlier than some scientists previously thought, the findings support the idea that they lived alongside humans, who arrived in Europe about 45,000 to 43,000 years ago. Rather than being replaced rapidly by modern humans, their disappearance occurred at different times across sites from the Black Sea to the Atlantic.
“We believe we now have the first robust timeline that sheds new light on some of the key questions around the possible interactions between Neanderthals and modern humans,” said Thomas Higham, an archaeologist at Oxford who led the study, published Wednesday in the journal Nature.
While it is known that Neanderthal genes have survived in the DNA of many modern humans to this day, suggesting that at least some interbreeding took place, scientists are still unclear about the extent of contact and the reasons why Neanderthals vanished. Recent studies have suggested between 1.5 and 2.1 percent of the DNA of modern non-African human populations originates from Neanderthals.
“In a way, our close cousins, as Neanderthals are, aren’t extinct,” Higham said. “They carry on in us today.”
Jean-Jacques Hublin, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who wasn’t involved in the study, said, “These new results confirm a long-suspected chronological overlap between the last Neanderthals and the first modern humans in Europe.”
Apart from narrowing the length of time that the two species existed alongside each other to between 2,600 and 5,400 years, Higham and his colleagues also believe they have shown that Neanderthals and humans largely kept to themselves.
“What we don’t see is that there is spatial overlap (in where they settled),” said Higham.
This is puzzling, because there is evidence that late-stage Neanderthals were culturally influenced by modern humans. Samples taken from some Neanderthal sites include artifacts that look like those introduced to Europe by humans migrating from Africa.
This would point to the possibility that Neanderthals — whose name derives from a valley in western Germany — adopted certain human habits and technologies even as they were being gradually pushed out of their territory.
“I think they were eventually outcompeted,” said Higham.
Many scientists now reject the notion that Neanderthals were dim-witted brutes and point to evidence of use of symbolic objects, which may have been learned from modern humans.
The Oxford team dated a number of items from sites of so-called transitional stone tool industries — viewed as either the work of the last of the Neanderthals or early modern humans — and found they were all between 40,000 and 45,000 years old, indicating a period of possible cultural exchange.
Paleoanthropologist Chris Stringer of the Natural History Museum in London, who was not involved in the research, said the new findings were “striking” and backed up the idea that modern humans and Neanderthals may have learned from each other.
He believes interbreeding probably first occurred in Asia soon after modern humans began to leave Africa around 60,000 years ago, so the latest evidence indicates the two populations may have been in some kind of contact for up to 20,000 years — much longer than in Europe alone.
Wil Roebroeks, an archaeologist at Leiden University in the Netherlands, cautioned that the study relies to a large decree on testing of stone tools, rather than bones, and these haven’t been conclusively linked to particular species, or hominins.
“The results of this impressive dating study are clear, but the assumptions about the association of stone artifact with hominin types underlying the interpretation of the dating results will be undoubtedly rigorously tested in field- and laboratory work over the near future,” said Roebroeks, who wasn’t involved in the study. “Such testing can now be done with a chronologically clean slate.”
While the latest work provides the most robust timeline so far of the last days of the Neanderthals, there are still gaps in coverage, particularly in Siberia and eastern regions of Eurasia. That is something the researchers plan to address in follow-up investigations.
“Ultimately, our aim is to create kind of movies that show the arrival and departure of different subspecies of humans across Europe,” Higham said. “We are partway toward that, but there is a still a lot more work we can do.”