"What evolutionary sense can we make of humor?"There is no doubt that there is a physiological element to laughter and whenever there is something built in, the temptation is always there to try to explain it in terms of natural selection. Alastair Clarke, for example, makes the case that humor is the brain's way of rewarding itself for seeing new patterns.
“The development of pattern recognition as displayed in humour could form the basis of humankind’s instinctive linguistic ability. Syntax and grammar function in fundamental patterns for which a child has an innate facility. All that differs from one individual to the next is the content of those patterns in terms of vocabulary.”It is an interesting conjecture, but like so much evolutionary psychology, little more than a just-so story.
It is certainly the case that certain heritable properties have been selected for in terms of their ability to aid in survival and reproduction, but that does not mean that every trait for which we can find advantageous was itself selected for. It may be an evolutionary free rider, that is, something that came along with other traits that were selected for.
There is no doubt that certain kinds of humor are as Clarke points out connected with intellectual abilities that would have given our ancestors certain advantages. Although I'm not sure that finding someone else's slipping on a banana peel and falling into a large pile of lion dung only to have a chimp pelt him with rotten fruit while on a hunt in the jungle necessarily conveys anything useful, but it would certainly be recounted around the fire for years to howls of approval.
The historical developmental case would have to be made with evidence that may or may not be there. These sorts of claims are notoriously difficult to establish, but it is certainly possible. Finding things funny does develop alongside language, so the question of what is responsible for what and what was the trait actually selected for is an interesting one. Either way, it certainly is natural.