If the Mona Lisa is the world’s most instantly recognizable piece of art, then what’s the best-known piece of art to come from America? That’s easy: It’s the painting that won third place in the Art Institute of Chicago’s 43rd annual exhibition on American paintings and sculpture, in 1930. You know the one. You’ve seen it hundreds of times before: American Gothic, by Grant Wood. This fall marks the 75th anniversary of the painting’s bronze-medal performance, and Harvard scholar Steven Biel marks the occasion with a short book on its curious history, American Gothic: A Life of America’s Most Famous...