While interbreeding between two human ancestors may have helped modern man's immune system, it may have also led to allergies.

Published in The American Journal of Human Genetics, the new study detailed how Neanderthals interbred with Denisovans some 40,000 years ago. For their research, the study authors analyzed DNA from modern humans and from their ancient relatives.

"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," study co-author Janet Kelso, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, said in a press release. "What has emerged from our study as well as from other work on introgression is that interbreeding with archaic humans does indeed have functional implications for modern humans, and that the most obvious consequences have been in shaping our adaptation to our environment - improving how we resist pathogens and metabolize novel foods."

The researchers were able to identify a small bit of DNA in modern humans inherited from Neanderthals that helped with their immune system.

"The evidence suggests that this genetic region contributes to the immune system of modern day humans," study co-author Michael Dannemann a Max Planck Institute colleague of Kelso's, told BBC News. "At some point in history it might have been an advantage to have these Neanderthal genes in terms of fighting off infections or lethal pathogens from 10,000 years ago.

"It could also still be an advantage today but this is difficult to pinpoint."