A stretch of DNA linked to Covid-19 was transferred from Neanderthals 60,000 years ago, according to a new study.
Researchers do not yet know why this segment increases the risk of serious coronavirus disease. But the new results, which were published online on Friday and have not yet been published in a scientific journal, show how some clues to modern health derive from ancient history.
“This breeding effect that occurred 60,000 years ago is still affecting today,” said Joshua Akey, a geneticist at Princeton University who did not participate in the new study.
Elsewhere, however, the segment is much less common. Only 8 percent of Europeans carry it and only 4 percent have it in East Asia. It is almost completely absent in Africa.
It is not clear which evolutionary pattern produced this distribution over the past 60,000 years. “That’s the question of $ 10,000,” said Hugo Zeberg, a geneticist at the Karolinska Institute in Sweden who was one of the authors of the new study.
One possibility is that the Neanderthal version is harmful and has become worse for everyone. It is also possible that the segment improved human health in South Asia, perhaps providing a strong immune response to viruses in the region.
“It should be emphasized that this is pure speculation,” said Dr. Zeberg’s co-author, Svante Paabo, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Researchers are beginning to understand why Covid-19 is more dangerous for some people than others. Older people are more likely to become seriously ill than younger ones. Men are more at risk than women.
Social inequality is also important. In the United States, black people are much more likely than white people to be seriously ill by the corona virus, for example, probably in part because of the country’s history of systemic racism. It has left black people with a high frequency of chronic diseases such as diabetes, as well as living conditions and jobs that can increase exposure to the virus.
Genes also play a role. Last month, researchers compared people in Italy and Spain who became very ill with Covid-19 to those with only mild infections. They found two sites in the genome that are associated with a greater risk. One is on chromosome 9 and includes ABO, a gene that determines blood type. The other is the Neanderthal segment on chromosome 3.
But these genetic findings are updated quickly as more people infected with coronavirus are studied. Just last week, an international group of researchers called the Covid-19 Host Genetics Initiative released a new set of data that reduces the risk of blood type. “The jury is still out on ABO,” said Mark Daly, a geneticist at Harvard Medical School who is a member of the initiative.
The new data showed an even stronger link between the disease and the segment Chromosome 3. People who carry two copies of the variant are three times more likely to suffer from serious illness than people who do not.
After the new database was released on Monday, Dr. Zeberg to find out if the Chromosome 3 segment was handed over from the Neanderthals.
Some 60,000 years ago, some ancestors of modern humans expanded out of Africa and swept across Europe, Asia and Australia. These people bumped into the Neanderthals and mingled. When Neanderthal DNA entered our gene pool, it spread through the generations, long after Neanderthal was eradicated.
Most Neanderthal genes were found to be harmful to modern humans. They may have been a burden to human health or made it more difficult to have children. As a result, Neanderthal genes became rare, and many disappeared from our gene pool.
But some genes appear to have given evolutionary advantage and become quite common. In May, Dr. Zeberg, Dr. Paabo and Dr. Janet Kelso, also from the Max Planck Institute, states that one-third of European women have a Neanderthal hormone receptor. It is associated with increased fertility and fewer miscarriages.
Dr. Zeberg knew that other Neanderthal genes that are common today also help us fight viruses. When modern humans expanded into Asia and Europe, they may have encountered new viruses against which Neanderthals had already developed defenses. We have held on to those genres ever since.
Dr. Zeberg looked at chromosome 3 in an online database of Neanderthal genomes. He found that the version that increases people’s risk of serious Covid-19 is the same version found in a Neanderthal who lived in Croatia 50,000 years ago. “I texted Svante immediately,” Dr. Zeberg said in an interview, citing Dr. Paabo.
Dr. Paabo was on holiday in a cabin in the remote Swedish countryside. Dr. Zeberg showed up the next day, and they worked day and night until they published the study online on Friday.
“It’s the most crazy vacation I’ve ever had in this cabin,” Dr. Paabo.
Tony Capra, a geneticist at Vanderbilt University who was not involved in the study, thought it was likely that the Neanderthal portion of DNA originally provided an advantage – perhaps even against other viruses. “But that was 40,000 years ago, and here we are now,” he said.
It is possible that an immune response that worked against old viruses has finally reacted to the new coronavirus. People who develop severe cases of Covid-19 usually do so because their immune system initiates uncontrolled attacks that ultimately scar the lungs and cause inflammation.
Dr. Paabo said the DNA segment may partly explain why people of Bangladeshi origin die to a great extent Covid-19 in the UK.
It is an open question whether this Neanderthal segment continues to maintain a strong connection to Covid-19 when Dr. Zeberg and other researchers are studying more patients. And it may take discoveries of the segment of ancient fossils of modern humans to understand why it became so common in some places but not in others.
But Dr. Zeberg said that the 60,000-year-old journey with this DNA part of our species can help explain why it is so dangerous today.
“Its evolutionary history can give us some clues,” Dr. Zeberg.
[[[[Like the Science Times page on Facebook. | Sign up for Science Times newsletter.]