You Have Allergies Because Your Ancestors Had Sex With Neanderthals

That's what a study says, at least.

Why Do Humans Have Allergies? Your Ancestors Had Sex With Neanderthals Volodymyr TVERDOKHLIB / Shutterstock

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 why do humans have allergies?

We know there is a reason for these types of allergies. We know why your throat closes and why it's hard to breathe when you eat or inhale something you are allergic to, and why you swell up if you are stung or bitten by certain insects.


And it all started out tens of thousands of years ago when our ancestors made contact with Neanderthals.

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There is a very probable reason why humans develop allergies altogether. And it comes down to our ancestors having had sex with Neanderthals more than 40,000 years ago.


A 2014 study performed by the genetics company 23andMe believed that 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.

But a 2016 study conducted by the American Journal of Human Genetics found it's more likely that 2 percent of most people's DNA came from sexual relations between humans and Neanderthals.

The 2014 study 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."

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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.


The 2016 study found that, besides giving you allergies, the Neanderthal part of your DNA may actually help you fight diseases.

The geneticists believe that there is a group of genes in our DNA that we inherited from Neanderthals that is the first line of defense against dangerous pathogens that enter our body, granted these genes also affect people's allergies.

Janet Kelso, a researcher at the Max Planck Institute for Evolutionary Anthropology, said, "Increased resistance to bacterial infection was advantageous, but may have resulted in some increased sensitivity to non-pathogenic allergens." 

These genes establish an innate immune response to pathogens that invade our bodies.


The innate immune response is the first line of defense our body has against disease. Usually, it can destroy pathogens way before we realize we are even sick.

Since the Neanderthals introduced this response into human DNA, it has survived this long because of natural selection and the idea of survival of the fittest.

So, those who are not killed by the disease, those who have an innate immune response are able to procreate and pass on the genes. That's why we still see the reoccurance of Neanderthal genes in modern people.


If you've developed allergies in your lifetime, you have your ancestors to thank for that.

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Editor's Note: This article was originally posted in January 2016 and was updated with the latest information

Samantha Maffucci is an editor for YourTango who has written hundreds of articles about relationships, trending news and entertainment, and astrology. Visit her author profile for more content.