Long ago, I read that certain African peoples cannot tolerate dairy products, seemingly because their ancestors had never been that kind of farmer. This is opposed, of course, to tribes like the Masai, who largely live on the stuff.
Here in NZ, many polynesian immigrants and their offspring display a distressing tendency to Gout when they live on the western diet, particularly American-style fast-foods like Kentucky Fried and the Big Mac's which they love so much.
Just another red herring in this Irish Stew.