Ever wonder what – or who – is to blame for your peanut allergy or inability to walk through a garden in spring without sneezing?

You can thank the Neanderthals for that.

Interbreeding with Neanderthals could be responsible for allergies on modern humans.

Human's distant and extinct cousins, along with another long-gone species of human, Denisovans, have seemingly passed on a gene that has had a significant impact on homosapiens' immune system. That gene is believed to be responsible for the some people's sensitivities to things such as pollen, peanuts and eggs.

But, on the flip side, those same genes now help humans in the fight against some diseases related to bacteria, fungus and parasites.