A bit of prehistoric hanky-panky between our ancestors and archaic humans may be responsible for the robust immune systems that many of us enjoy today.
A study published Friday in the journal Science has provided convincing evidence that many people carry variants of immune-system genes that originally came from Neanderthals and related archaic humans known as Denisovans who once roamed across Eurasia.
These genes suggest there must have been crossbreeding between anatomically modern humans and their close cousins on the evolutionary tree, according to the team of researchers led by Laurent Abi-Rached and Peter Parham of Stanford University School of Medicine in California.
The findings are based on a comparison of genes from a cross-section of people living today and DNA extracted from the fossil remains of Neanderthals and the recently discovered Denisovans. The analysis focused on certain HLA genes, which play a key role in helping the body’s immune system recognize and destroy pathogens.
The crossbreeding likely occurred relatively soon after modern humans left Africa about 65,000 years ago, said Paul Norman, a Stanford scientist who was on the research team.
“We think the new gene variants acquired from the Neanderthals and Denisovans helped provide resistance to diseases that were present outside of Africa,” he said. “These archaic humans had been in Eurasia for 200,000 years before we got there, so that was quite a long time for them to adapt to the new viruses.”
Although the sexual encounters of modern and archaic humans may have been few and far between, the resulting offspring were genetically well equipped to survive in the new environment, the researchers speculate. Their descendants, went on to colonize the rest of the world.
Some of the acquired gene variants are widely distributed among people around the globe today, but absent from most of Africa.
Modern humans, Neanderthals and Denisovans all shared a common ancestor in Africa long ago. They split into separate groups, with the Neanderthal lineage heading to Europe and West Asia and the Denisovans migrating to Northern Asia. When modern humans finally emerged from Africa, they had the opportunity to once again encounter these other groups – occasionally becoming kissing cave-cousins.
Dr. Norman noted that his own HLA genes “are 75 per cent of Neanderthal origin.”