Did modern humans (left) kill off Neanderthals (right)? Sabena Jane Blackbird/Alamy

Neanderthals may have died out not because of competition from our species, but simply through sheer bad luck. A simulation of their population suggests that they were always vulnerable to extinction and random chance was enough to tip them over the edge.

Neanderthals lived in Europe and Asia for hundreds of thousands of years. However, their population was always small, probably just a few thousand, and they died out about 40,000 years ago.

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At this time modern humans were entering Europe from Africa in large numbers for the first time. As a result, many researchers suspect that our species is to blame for the Neanderthals’ demise. This doesn’t necessarily mean that humans killed them – it could be that humans were smarter and outcompeted them.


But Krist Vaesen of Eindhoven University of Technology in the Netherlands and his colleagues think we aren’t to blame. They simulated the Neanderthal population based on DNA records, tracking how many were born and died each year, and how closely related they were, using estimates based on modern humans.

This allowed the researchers to track three processes that they believe made the Neanderthals vulnerable. The first is inbreeding, which can lead to a build-up of harmful mutations. “In a small population, the chances you mate with a relative are higher,” says Vaesen.

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The second is a phenomenon called the Allee effect. “If you’re in a small population, you have higher problems with finding a suitable mate,” says Vaesen, simply because you won’t have many options.

Finally, there is random chance: for instance, unusually high death rates in a single year. For a small and isolated population, one bad year can be catastrophic.

“We ran those models for 10,000 years and looked at whether they would go extinct or not,” says Vaesen. “We found that these three processes were enough to do the trick.”

The model doesn’t prove that modern humans didn’t compete with Neanderthals, Vaesen emphasises. It simply shows that this competition isn’t necessary to explain the extinction.

Vaesen says it remains striking that Neanderthals died out so soon after humans arrived, but competition for resources might not be the reason.

“We know that Neanderthals lived in small sub-populations and that they were dispersed over Europe,” he says. The presence of humans might have made it harder for Neanderthals to move between groups, forcing each sub-population to stand alone and exacerbating inbreeding, the Allee effect and the effects of bad years. “That might have been enough,” he says.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0225117