This one always caught my attention. In my personal experience, none of my friends growing up in Mexico were allergic to peanuts. I didn't even know such a thing existed. I'd go to summer camp in Mexico and nobody was allergic. Then I go to summer camp in the US and peanut allergy is a huge deal over here. Genetics? No. In both camps we were mostly ashkenazi jews with the same exact genetic makeup. In Israel? Again, same genetic makeup, and kids gobble up peanut-made Bamba since very early. To me this is clear indication of an environmental factor. Which means that it can be corrected / adjusted.