Deborah Netburn, Los Angeles Times, January 8, 2016

If you sneeze when flowers bloom in the spring and tear up in the presence of a cat, your Neanderthal DNA may be to blame.

About 2% of the DNA in most people alive today came from trysts between ancient humans and their Neanderthal neighbors tens of thousands of years ago, recent studies have shown. Now, scientists are trying to determine what, if any, impact that Neanderthal genetic legacy has on our contemporary lives.

In a pair of papers published this week in the American Journal of Human Genetics, two research teams report that in many people, a group of genes that govern the first line of defense against pathogens was probably inherited from Neanderthals.

These same genes appear to play a role in some people’s allergic reaction to things like pollen and pet fur as well, the scientists said.

“It’s a bit speculative, but perhaps this is some kind of trade-off,” said Janet Kelso, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and senior author of one of the new studies. “Increased resistance to bacterial infection was advantageous, but may have resulted in some increased sensitivity to non-pathogenic allergens.”

About 50,000 years ago, the modern humans who left Africa encountered Neanderthal settlements somewhere in the Middle East, scientists believe. On some occasions, these meetings led to couplings whose legacy is apparent in the genomes of people with ancestors from Europe and Asia.

Not everyone with Neanderthal DNA inherited the same genes. But the immunity genes appear to be more popular than others.

Among some Asian and European populations, the researchers found that these particular Neanderthal genes can be found in 50% of people.

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Because Neanderthals had lived in Europe and western Asia for about 200,000 years before modern humans got there, they were probably already well adapted to the local climate, foods and pathogens.

“By interbreeding with these archaic people, modern humans could then acquire some of these adaptations,” Kelso said.

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