Coronavirus: Neanderthal interbreeding ‘raised risk of severe Covid’

This year could have gone very differently if some of our ancestors had not been quite so oversexed 60,000 years ago.

This year could have gone very differently if some of our ancestors had not been quite so oversexed 60,000 years ago.

Common genes that double the risk of severe COVID-19 came to us because of interbreeding with Neanderthals, scientists have said. These genes can be found in about one in six ethnic Europeans and one in two south Asians. They occur at the highest frequency in Bangladesh, where they are present in almost two thirds of the population.

Previous studies of thousands of people infected with coronavirus have shown that the presence of the gene variants appeared to double the risk of suffering severe COVID-19, an unusually high effect for a few genes. “It’s striking to see such a strong effect of genetic variance, a twofold risk,” Hugo Zeberg, of the Max Planck Institute for Evolutionary Anthropology, said. “It is really a surprise to us.”

In a study published in the journal Nature, he and his colleagues have pinned down the source.

A replica of a Neanderthal man at the Neanderthal museum in Mettmann, western Germany. Picture: AP.

When they looked at the genome of a Croatian Neanderthal, an evolutionary cousin of our own species, Homo sapiens, they had another surprise. “We just compared it and realised, ‘Oh gosh, it’s all Neanderthals’.”

People of European ancestry as well as some Asians have between 1 per cent and 2 per cent of their DNA in common with Neanderthals, a species of human that became extinct 40,000 years ago. This is proof that after humans left Africa, about 60,000 years ago, the two species interbred.

The genes that remain from that coupling appear to be those that have, until now, been useful to humans, perhaps because they have helped us to survive disease or cold weather. Professor Zeberg said it was not clear what the specific Covid-risk genes were doing, but he and his colleagues had a theory.

“It’s so frequent in Bangladesh … that that suggests it had a role in the past. The first thing that comes to mind is protection against other pathogens. Cholera is very common here and some evidence points towards it. That’s our hypothesis.”

Counterintuitively, if the genes do boost the immune response to cholera it might also explain why it would have a negative role to play in COVID-19. “The immune system is in a constant balance with its surroundings. You want it to work to just the right amount,” Professor Zeberg said. “One characteristic of severely ill people is they have an overactive immune response.”

Professor Zeberg added: “We see that just a few gene variants cause a severe outcome … Although we find it very interesting, interbreeding with Neanderthals had tragic consequences for the current pandemic.”

The Times