Modern humans and
Neanderthals could be forgiven for having other issues on their
minds when they interbred in the stone age. But according to
researchers, those ancient couplings laid a grim foundation for
deaths around the world today.
Scientists have claimed that a strand
of DNA that triples the risk of developing
severe Covid-19 was passed on from Neanderthals to modern
humans. The genetic endowment, a legacy from more than 50,000 years
ago, has left about 16% of Europeans and half of south Asians today
carrying these genes.
The origins of the risk genes
came to light when scientists in Sweden and Germany compared the DNA
of very sick Covid-19 patients with that from Neanderthals and their
mysterious sister group, the Denisovans デニソワ人.
The stretch of DNA that makes patients more likely to fall seriously
ill closely matched that collected from a Neanderthal in Croatia.
“I almost fell off my chair
because the segment of DNA was exactly the same as in the
Neanderthal genome,” Hugo Zeberg, an assistant professor at the
Karolinska Institute in Stockholm, told the Guardian.
Zeberg and his co-author, Svante
Pääbo, director of the Max Planck Institute of Evolutionary
Anthropology in Leipzig, suspect the Neanderthal genes have
persisted in modern humans because they were
once beneficial, perhaps helping to fight off other
infections. Only now – when faced with a new infection – has their
downside been exposed.
It is unclear how the genes may
worsen Covid-19, but one gene plays a role in the immune response
and another has been linked to the mechanism the virus uses to
invade human cells. “We are trying to pinpoint which gene is the key
player, or if there are several key players, but the honest answer
is that we don’t know which are critical in Covid-19,” Zeberg said.
According to the study, published
in Nature, the cluster of genes on chromosome
three are most commonly found in Bangladesh, where 63% of the
population carry at least one copy of the DNA sequence.
“The genes in this region may
well have protected the Neanderthals against some other infectious
diseases that are not around today. And now, when we are faced with
the novel corona virus these Neanderthal genes have these tragic
consequences,” Pääbo said.
The researcher, who led the
international team that first deciphered the Neanderthal genome in
2010, said his “rough estimate” was that about 100,000 “additional”
people have died so far in the current pandemic due to the genetic
contribution from Neanderthals.
Beyond the Covid-19 risk genes,
the Neanderthals have bequeathed other genes to modern humans. Some
increase sensitivity to pain, while others reduce the risk of
miscarriages. “Some are beneficial and some are detrimental,” Zeberg
said. “This has been a double-edged sword.”
But Mark Maslin, a professor at
UCL and author of the book The Cradle of Humanity, cautioned that
the work risked oversimplifying the causes and impact of the
pandemic. “Covid-19 is a complex disease, the severity of which has
been linked to age, gender, ethnicity, obesity, health, virus load
among other things,” he said.
“This paper links genes inherited
from Neanderthals with a higher risk of Covid-19 hospitalisation and
severe complications. But as Covid-19 spreads around the world it is
clear that lots of different populations are being severely
affected, many of which do not have any Neanderthal genes.
“We must avoid simplifying the
causes and impact of Covid-19, as ultimately a person’s response to
the disease is about contact and then the body’s immunity response,
which is influenced by many environmental, health and genetic
factors.”
