Neanderthals, as well as hominids known as Denisovans, contributed key types of immune genes still found in human populations, scientists say.As recently as 2008, scientists thought that Neanderthals and modern humans had never mated.
Then, last year, they said that the two species had, but that the few Neanderthal genes that survived in modern human DNA were not functional.
Now researchers believe that key versions of immune system genes in modern humans appear to have been passed down by archaic relatives, including Neanderthals, after all.
Indeed, DNA inherited from Neanderthals and newly discovered hominids dubbed the Denisovans has contributed to key types of immune genes still present among populations in Europe, Asia and Oceania. And scientists speculate that these gene variants must have been highly beneficial to modern humans, helping them thrive as they migrated throughout the world.
This DNA has had “a very profound functional impact in the immune systems of modern humans,” said study first author Laurent Abi-Rached, a postdoctoral researcher in the lab of senior author Peter Parham of the Stanford University School of Medicine.
Neanderthals were stocky hunter-gatherers who populated Europe and parts of Asia until about 30,000 years ago. In 2010, a team of biologists led by Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, sequenced the Neanderthal genome via DNA extracted from ancient bones.
From this, they estimated that 1% to 4% of modern Eurasian genomes came from our close hominid relatives.
No one knows what Denisovans looked like: The only confirmed evidence of the group, which is thought to have split from the Neanderthals about 350,000 years ago and migrated east, are a tooth and a pinkie finger bone found in a Siberian cave in 2008.
When Paabo and coworkers sequenced DNA extracted from the pinkie in 2010, they calculated that 4% to 6% of modern Melanesian genomes came from Denisovans.
In the new study, Abi-Rached and coauthors decided to focus on a small set of genes on chromosome 6 known as the human leukocyte antigen (HLA) class I genes.
HLA genes carry instruction for making HLA proteins, which help the immune system spot evidence of problems in cells â€” infection or cancer, for instance â€” so that it can wipe out abnormalities to fight disease. The genes come in many forms that vary in frequency around the world, probably because our genomes have been tailored by evolution to fight specific disease threats that exist in particular places. …