Interbreeding between Neanderthals and ancient humans, thousands of years ago in Europe, may have given humans increased immunity. This gene variation could also have left modern people more prone to allergies such as sneezes and itches.

The findings from the study said that ancient humans and their distant ancestors had sexual encounters with Neanderthals or with Denisovans, their close relatives, about 40,000 years ago. Due to this prehistoric coupling, three genes crossed into modern humans, and has left all non-Africans carrying 1-6 percent of Neanderthal DNA. Researchers studied a list of 1,500 genes that played a role in the innate immune system.

“These, and other, innate immunity genes present higher levels of Neanderthal ancestry than the remainder of the coding genome,” said Lluis QuintanaMurci of the Institute Pasteur and the CNRS in France.

The three gene strands, commonly found in Neanderthal DNA, played an important role in human evolution. They could have boosted the immune system as genes are the first to act against pathogens such as bacteria and fungi. However, people who carry these three genes, have an overly immune system, and were more likely to have allergies such as asthma, hay fever and other allergies.

Janet Kelso of the Max Planck Institute for Evolutionary Anthropology, Germany said that the Neanderthals and Denisovans influenced the present-day genomes at three innate immunity genes belonging to the humans Toll-like-receptor family. Kelso’s team analysed the genes of modern humans for evidence of Neanderthals or Denisovans genes, and looked at their incidence in people around the world. Kelso added that the interbreeding did have “functional implications” for modern human beings.

However, the Neanderthals genes might not be so bad as they have increased our susceptibility. The genes have been beneficial that they remain in the present day. the study has been published in the American Journal of Human Genetics.