Sleeping around can expose you to diseases, but, at least in the course of human evolution, it may help you fight ’em. New research suggests that thousands of years ago humans acquired important immune system genes via liaisons with some of our extinct hominid cousins, the Neandertals and Denisovans. These dalliances may have allowed modern humans to persist in regions where unfamiliar pathogens may have otherwise killed them.
Many modern human populations appear to have the same versions of certain immune system genes found in those archaic relatives, a team of researchers reports online August 25 in Science. The Neandertal and Denisovan versions are most prevalent in modern populations in Europe and Asia. Because modern African populations harbor little to none of these archaic gene variants, the discovery suggests that humans acquired them after heading out of Africa and running into Neandertals and Denisovans in Europe and Asia.
“It’s amazing stuff,” says Daniel Geraghty, a specialist in genetics and immunology at the Fred Hutchinson Cancer Research Center in Seattle. “They have done a really great job of weaving together facts to come up with a very plausible and very powerful story of what might have happened to the human species as it expanded out of Africa.”
Previous research suggested that humans were interbreeding with both Neandertals and Denisovans, a closely related species known only from a fossil finger bone found in a Siberian cave. Modern Eurasian genomes contain up to 4 percent of Neandertal DNA, and the DNA of Melanesians of Papua New Guinea is 4 to 6 percent Denisovan (SN: 6/5/10, 1/15/11).