New studies suggest three genes from Neanderthals may be responsible for human allergies. Photo by life_in_a_pixel/Shutterstock

LEIPZIG, Germany, Jan. 7 (UPI) -- Previous genetic studies have proven early humans interbred with both Neanderthals and their close relatives the Denisovans. New research suggest these encounters may be to blame for allergies.

A team of international scientists identified three genes in the DNA of Neanderthals and Denisovans most commonly found in humans. These genes helped boost human immune defenses, protecting us against bacterial and viral pathogens.


But for some unlucky inheritors, the presence of all three immune-boosting genes has proven to be too much, enabling an overly sensitive immune system.

All in all, researchers say interbreeding was a smart strategy for the early humans who moved out of Africa and into Eurasia.

"A small group of modern humans leaving Africa would not carry much genetic variation," lead researcher Janet Kelso, an evolutionary anthropologist at the Max Planck Institute in Leipzig, told The Guardian. "You can adapt through mutations, but if you interbreed with the local population who are already there, you can get some of these adaptations for free."

The Neanderthals and Denisovans had been living in Eurasia for 200,000 years before early humans arrived on the continent 40,000 years ago.

But the same genes that protected those early humans made them sensitive to animal hair and pollen.

To what extent do those three genes still dictate our immune response today? Researchers are trying to figure that out. Most scientists think there's a lot more to learn about human-Neanderthal interbreeding and how it countinues to influence genomes today.

"I think this is really just the tip of the iceberg about how mating with Neanderthals influences all sorts of traits today," Josh Akey, a professor of genome sciences at the University of Washington who did not participate in the new research, told NPR.

The new findings were detailed in two papers published this week in the journal American Society of Human Genetics.