A stretch of DNA connected to Covid-19 was passed down from Neanderthals 60,000 years past, according to another study.
Scientists don’t yet know why this specific segment increases the probability of severe illness from the coronavirus. But the brand new findings, that have been published online on Friday and haven’t yet been printed in a scientific journal, show how some clues to modern health stem from ancient history.
“This interbreeding effect that happened 60,000 years ago is still having an impact now,” explained Joshua Akey, a geneticist at Princeton University who wasn’t involved in the new study.
This piece of the genome, which crosses six genes on Chromosome 3, has experienced a vexing journey through human history, the study found. The version is now common in Bangladesh, in which 63 percent of people carry at least one copy. Across all South Asia, almost one-third of people have inherited the section.
Elsewhere, however, the section is far less common. Just 8 percent of Europeans carry this, and just 4 percent have it in East Asia. It is almost totally absent in Africa.
It’s not clear what evolutionary pattern generated this supply over the past 60,000 years. “That is the 10,000 question,” said Hugo Zeberg, a geneticist at the Karolinska Institute in Sweden that had been one of the authors of this new study.
One possibility is that the Neanderthal variant is detrimental and has been becoming rarer over all. Additionally, it is possible that the segment improved people’s health in South Asia, possibly offering a powerful immune response to viruses in the area.
“One should stress that in this point that is pure speculation,” explained Dr. Zeberg’s co-author, Svante Paabo, the manager of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Researchers are only starting to understand why Covid-19 is significantly more dangerous for some people than others. Individuals are more likely to become ill. Men are at more risk than women.
Social inequality matters, also. In the United States, Black men and women are far more inclined than elderly individuals to become severely ill from the coronavirus, for example, most likely due in part to the nation’s history of systemic racism. It’s left living conditions and tasks, in addition to a high rate of chronic diseases like diabetes that may increase exposure to the virus to Black people.
Genes play a role as well. Last month, researchers compared individuals in Italy and Spain who became really sick with Covid-19 to people who had only mild infections. They discovered two areas in the genome associated with a increased risk. One is on Chromosome 9 and includes a gene that determines blood flow, ABO. Another is the Neanderthal segment on Chromosome 3.
But these genetic findings are being rapidly updated as more individuals infected with the coronavirus are analyzed. Only last week, an international group of scientists called the Covid-19 Host Genetics Initiative released a new set of information downplaying the possibility of blood kind. “The jury remains out on ABO,” said Mark Daly, a geneticist at Harvard Medical School who’s a member of this initiative.
The new data showed an even stronger link between the disease and the Chromosome 3 section. People who carry two copies of the variant are 3 times more likely to suffer from acute illness.
After the new batch of data came out on Monday, Dr. Zeberg chose to discover whether the Chromosome 3 section was passed from Neanderthals.
About 60,000 years ago, a few ancestors of modern humans expanded from Africa and hauled across Europe, Asia and Australia. These people interbred and struck Neanderthals. It spread down through the generations after Neanderthals became extinct once our gene pool was entered by Neanderthal DNA.
Most Neanderthal genes proven to be harmful to modern humans. They made it harder to have kids or might have been a burden on people’s health. As a result, genes that were Neanderthal became rarer, and many disappeared out of our gene pool.
But some genes seem to have provided an evolutionary advantage and have become rather common. In May, Dr. Zeberg, Dr. Paabo and Dr. Janet Kelso, also of the Max Planck Institute, found that one-third of European women have a Neanderthal hormone receptor. It is associated with fewer miscarriages and greater fertility.
Dr. Zeberg understood that additional Neanderthal genes that are common now even help us combat viruses. They could have struck viruses against which Neanderthals had already evolved defenses when modern humans expanded into Asia and Europe. Those genes have been held onto by us since.
Dr. Zeberg looked at Chromosome 3 in an online database of Neanderthal genomes. He found that the version that raises people’s risk of acute Covid-19 is exactly the exact same version found at a Neanderthal who dwelt in Croatia 50,000 years past. “I texted Svante immediately,” Dr. Zeberg stated in an interview, referring to Dr. Paabo.
Dr. Paabo was on holiday in a cabin in the distant Swedish countryside. Dr. Zeberg showed up the next day, and they worked day and night till they posted the study online on Friday.
“It’s the most crazy vacation I’ve ever had in this cabin,” Dr. Paabo said.
Tony Capra, a geneticist at Vanderbilt University who was not involved in the analysis, believed it was plausible that the Neanderthal chunk of DNA originally supplied a benefit — perhaps even contrary to other viruses. “But that was 40,000 years ago, and here we are now,” he said.
It’s possible that an immune response that worked against ancient viruses has ended up overreacting against the new coronavirus. People who develop severe cases of Covid-19 typically do this because their immune systems establish uncontrolled attacks that end up scarring their lungs and causing inflammation.
Dr. Paabo said the DNA segment might account in part for why individuals of Bangladeshi descent are expiring at a high rate of Covid-19 in the United Kingdom.
It is an open question whether this Neanderthal segment continues to maintain a strong link to Covid-19 as Dr. Zeberg and other investigators study more patients. And it might take discoveries of the segment in fossils of modern humans to understand why it became so common.
But Dr. Zeberg explained that the 60,000-year journey of this chunk of DNA within our species might help clarify why it is so dangerous now.
“Its history may give us some hints,” Dr. Zeberg said.