I finally know why so many Indian dishes have curry in them
There's a scientific explanation for spicy food.
Basically, places with hot climates develop spicy food. (Which, at least passes the common sense test: South- and Central-American foods, Indian foods are spicy, etc.) Spices also have a high correlation with bacteria destruction. In other words, curry drives away bacteria. So, people in hot climates eat spicy foods because, essentially, their food goes bad faster and the spices keep it healthy.
(They said they looked at whether it just "covered up" bad food, but that didn't hold up — if they were just eating spoiled food all the time, well, that's not very healthy.)
So, places like Germany and England and Switzerland have less spicy food because they have colder climates. They said they also found regional differences within larger countries like US and China. (Like, Louisiana gumbo is spicier than New England clam chowder.)
Basically, they suggest that what happened was Darwinian: One guy likes onions, jalepenos and whatever on his mastadon and just happens to outlive his neighbors who eat it raw. Then onion-guy teaches his kids the "proper" way to cook mastadon requires onion and curry or whatever, and in a few generations, the whole population is eating it that way. It becomes cuisine.