i've thought about this sooo many times. in an evolutionism setting as you also thought. the only thing i can think of is that it may have been used to stop conflicts. example: caveman 1 hits caveman 2 in the head accidentally with a rock, caveman 1 shakes his head and laughs, caveman 2 realizes its an accident, they are cool. i know its far fetched but its all i got so far lol
Well, it makes more sense than "so we don't kill ourselves". Again, the article I read on it mentioned that laughing was used as an indicator of something positive happening, like finding food, finding shelter, what have you. The article also mentioned that they had nothing to base this on. So no one really knows.