A new study, published in the journal Nature, suggests that humans and Neanderthals could have lived side by side in Europe for up to 5,000 years, much longer than previously believed.

William Davies, who wrote on editorial accompanying the paper, says the new research supports the theory that the two species met, interbred and even exchanged toolmaking techniques and artistic ideas across parts of Europe.

Neanderthals are modern humanity’s (Homo sapiens) closest cousins, sharing about 99.5 percent of our DNA. Scientists believe they originated in Africa and migrated to Europe at least 200,000 years ago, possibly tens of thousands of years earlier. Because Homo sapiens did not begin its northern migration until about 60,000 years ago, the two species evolved under very different conditions.

Previous research had suggested that modern humans arrived in Neanderthal-dominated Europe about 40,000 years ago. Based on more reliable dating techniques, researchers now push that estimate back to about 45,000 years.

5000 years is quite a long time in human terms, about 250 generations, explains Davies, an associate professor in the Department of Archaeology at the University of Southampton in the UK. Given this amount of time on the same continent, the two species may have had considerable influence on one another.

The new chronology gives scientists a new basis for “assessing just how much potential there was for overlap,” Davies says. “Therefore we can start looking more closely at the artifacts they left behind and seeing whether we can identify the exchange of ideas.”

During this period of human evolution Neanderthals and Homo sapiens shared many similarities — anatomically, physically and intellectually. “I like to tell my students that perhaps looking at Neanderthals [is] the closest we'll get to looking at an alien human intelligence. It's something that's like us, but not necessarily exactly like us. They're not just watered down versions of us — they're their own beings.”

The enduring mystery of the Neanderthals is why and how they died out within such a brief time span while homo sapiens survived. In theory, the Neanderthals, having adapted to conditions in Europe and possessed of equal intelligence and more physcial strength, should have been better equipped than Homo sapiens to survive.

“They ruled Europe and Asia for quite a long time before we showed up,” Davies says. “[T]hey reached from Spain and Portugal, into what is now Israel, and all across southern Siberia. They were very, very successful and we shouldn't underestimate that success.”

Davies says there are many possible reasons to explain why Neanderthals went extinct. A major climatic event, for example, or some other kind of natural disaster might have isolated small pockets of them, causing the population to rapidly shrink. Other researchers believe they vanished because our species, Homo sapiens, arrived and out-competed them.

“I think, like all explanations, it's probably a mixture of different factors, some environmental, some other human groups that had this effect on them — and probably it varied from region to region,” Davies says.

This story is based on an interview that aired on PRI's Science Friday with Ira Flatow