Global One (G1)—Scientists have long known how ancient humans and Neanderthals were close — very close — to each other, to the point where non-Africans have 2-3% Neanderthal DNA.

Now, new research shows just how beneficial that relationship was for us.

According to an Oct. 4 paper published in the journal “Cell,” ancient humans’ romantic encounters with Neanderthals has resulted in humans getting a tougher immune system.

Neanderthals would have already been immune to diseases in Europe by the time ancient humans left Africa — but humans were not.

Thanks to inbreeding, humans would eventually develop immunity to certain diseases.

Essentially, Neanderthals made humans sick — but then cured them over time.

David Enard, one of the paper’s authors, says, “We call it the poison-antidote model.”

In addition to solving questions about our past, Enard thinks the research will also help us with future epidemics.