Walking around in another country it is hard not to notice that faces have different shapes than I am used to. Nor is it just genetics. The American face is distinct -- loose, happy, and flabby -- but the country is quite recent and clearly there is no unique American race. (How long did it take for this face to arise?)
Peer effects, as passed down from older generations, are the obvious mechanism for how these faces get shaped. So sometimes when I walk around in other countries I see, in my mind's eye, the older people pulling on the faces of the younger. All over the street, I see face-pulling cosmic rays emanating from eyes of the older brothers, yanking and tugging on the skin of the younger brothers.
Does it ever hurt? How many other body parts get shaped this way?