Modern man cleared: inbreeding led to the fall of Neanderthals

New research suggests Neanderthals did not die out due to competition but because their DNA became too diluted.

A scene from TV’s "Walking with Cavemen"

Neanderthals were not wiped out by humans but instead may have mated themselves into oblivion, according to research that suggests that interbreeding was the real cause of their disappearance.

Genetic analysis of the fossilised remains of Neanderthals, early humans and modern humans indicates that rather than being killed or out-competed for resources, Neanderthals lost their identity as their DNA became ­diluted.

“It means they were incorporated, which is why we see so many of their genes living on in modern Europeans,” said Svante Paabo, professor of evolutionary genetics at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Neanderthals are thought to have evolved from early humans, who left Africa about 450,000 years ago.

They spread across Eurasia until modern humans arrived 60,000 years ago. About 30,000 years later they had vanished.

Professor Paabo led the team that decoded the Neanderthal genome in 2010, which showed that 2-3 per cent of the DNA in humans of modern European origin was Neanderthal. That small amount of DNA initially prompted scientists to assume that interbreeding was rare, but new evidence indicates a huge variety of Neanderthal genes survived. “If we look at a few thousand genomes, we can pick out 15,000 Neanderthal genes — so at least half their genome is walking around in people today,” said Professor Paabo.

The findings have prompted research into the role of Neanderthal genes today. One study, led by Michael Gregory of the US Nat­ional Institute of Mental Health, analysed people’s genomes to calculate their “NeanderScore”, or how much Neanderthal DNA they carried.

“A higher NeanderScore is associated with skull shapes resembling those of known Neanderthal cranial remains,” says the report.

“This suggests that Neanderthal- derived (genes) are neurologically functional in the contemporary population.”

There is also evidence linking Neanderthal genes with health problems. “Evidence suggests that certain variants inherited from Neanderthals have greater effect on illness such as high cholesterol, autism and depression,” said Ole Andreassen, of the Institute of Clinical Medicine at the University of Oslo in Norway.

“They have also given us immunity to some things while making us allergic to others and, surprisingly, increasing our risk of addiction to tobacco.”

Some researchers have tentatively linked levels of Neanderthal DNA in modern humans with character traits. “High Neanderthal quotients tend to correspond to social fear and to autistic and depressive tendencies,” said Glenn Geher, a professor of psychology at the State University of New York. “This is consistent with the conception of Neanderthals as being ill-suited for large-scale ­social living.”

The Sunday Times