alt Hacker NewsSilly theory for why minor sounds sad: Say "ah", like you've just discovered something interesting. Now say "ah" like you've been told something sad. Notice the pitch difference? And notice how both pitches are about a major third and minor third above normal speaking pitch. Whether that's hard-wired or cultural, I couldn't say. But it would certainly be an interesting thing to research and compare across cultures and musical traditions.
Harry Partch has a book Genesis of a Music, which is half autobiography and half a theory that all melody derives from the micro pitch variations of speech - as in melody is a stretched out version of how we speak. I don't know if this idea has ever been pursued more academically but I find it very interesting. If it's true, I also wonder if there's feedback, like our vocal inflections are influenced by music melodies just as much as vice versa.