When modern humans met Neanderthals in Europe and the two species began interbreeding many thousands of years ago, the exchange left humans with gene variations that have increased the ability of those who carry them to ward off infection. This inheritance from Neanderthals may have also left some people more prone to allergies.
The discoveries reported in two independent studies in the American Journal of Human Genetics on January 7 add to evidence for an important role for interspecies relations in human evolution and specifically in the evolution of the innate immune system, which serves as the body's first line of defense against infection.
"We found that interbreeding with archaic humans--the Neanderthals and Denisovans--has influenced the genetic diversity in present-day genomes at three innate immunity genes belonging to the human Toll-like-receptor family," says Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
"These, and other, innate immunity genes present higher levels of Neanderthal ancestry than the remainder of the coding genome," adds Lluis Quintana-Murci of the Institut Pasteur and the CNRS in Paris. "This highlights how important introgression events [the movement of genes across species] may have been in the evolution of the innate immunity system in humans."