CarlShuman, it seems to me that even the set of minds that would have received some fitness benefit from a sense of humor would be much smaller than the set of minds that actually have a sense of humor, since there are almost certainly lots of other ways to solve the kind of fitness problems that humor solves.

Also, the set of minds that would receive benefit from humor is way smaller yet than the whole of plausibly-biologically-evolved mindspace. For example, how would a non-social mind benefit from humor?