That's what a new study says, at least.
Those of us with peanut allergies know how difficult it is to avoid being around products containing peanuts. Chocolate bars, cereals, fried foods, and even kissing someone who's eaten something containing peanuts could cause an allergic reaction.
But now there might be an explanation for humans developing allergies altogether. And it comes down to our ancestors having had sex with Neanderthals more than 40,000 years ago.
Today, all non-African individuals carry between one to six percent of Neanderthal DNA, and three genes in particular in this DNA may be responsible for overly-sensitive immune systems that make us susceptible to allergies.
A study by the genetics company 23andme found that carriers of these three genes were more likely to have hay fever, asthma, as well as other allergies. Researchers theorize that the genes spread when pioneers who left Africa had sex with Neanderthals living in Eurasia. Since the Neanderthals lived in this area for over 200,000 years, their immune systems adapted to any new infections.
Janet Kelso, lead researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, said, "A small group of modern humans leaving Africa would not carry much genetic variation. 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 researchers looked at the genomes of modern humans to see if Neanderthal DNA was present; they then looked at the commonality among people from around the world. They found that two out of three immune system genes closely matched this DNA.
So, if you've developed allergies in your lifetime, you have your ancestors to thank for that.