How did laughter originate? Is man the only animal that shows its teeth when it is happy? During mans early development, what could have been funny? I guess that I am trying to figure out how early man, very early man, developed a sense of humor and decided to laugh at what he understood was humorous. It would appear to me that his lfe would be filled with struggle, survival, pain and death and not much time to consider anything funny.
Boy, THIS one’s headed for Great Debates. Time for some fun WAG’s. In days of yore ( like, 20,000 years ago ) one perhaps didn’t have formal language as such. I’d guess that we all had personalities, even if we could not communicate with anything more than facial gestures and primal sounds.
So, try this on for size: We have three prime specimens of early man. Let us call them…oh…Cartooniverse, CajunMan and Billdo . 
The following might transpire one day out on the veldt.
Cartooniverse drags a wildebeest back to the cave. Ahhh, fresh kill.
Billdo immediately gets the sharp flint.
CajunMan eyes the other two.
All of a sudden, Cartooniverse trips over the haunches of the dead wildebeest and falls flat on his face. Now, no words were exchanged but since the other two know Cartooniverse to be a skilled hunter, agile runner and all around fit fellah ( hey man, it’s MY story !!!), this fall was not in keeping with his normal pattern of behavior.
So, they laughed. It was a visual surprise, and of course also was an amusing commentary on Cartooniverse’s supposed agility, that he went and fell over a dead animal.
The element of surprise. The out-of-character moment. The victim’s reaction. ( In this case, Cartooniverse lay there grimacing as he scraped off the gooey blood he’d fallen into, internally wishing he’d discovered language so he could curse out the other two ).
My WAG is that laughter is an outgrowth of fear. I’m stealing from Mel Brooks here but hell, steal from the best!! A startled response, followed immediately by the relief of realizing that you are NOT about to be eaten by a sabre-toothed tiger leads to the flood of adrenaline with no where to go, and the release of the endorphines and whatnot that accompany extreme emotions. One laughs to relieve the tension- just like at that cocktail party you were at last week where your joke went over badly. You laughed at yourself to cover up extreme emotions.
Out of this stuff comes physical comedy. The Greeks had elevated written drama and comedy to a high art form. Then, silent films came along and what did we have? Lacking anything but dialogue cards, we got…slapstick. Physical reactions to stressful or dangerous moments made us laugh. They still do. Chevy Chase fell down when he was on SNL- pure gag comedy. We laughed at his skill to imitate someone falling down, we were relieved that he wasn’t hurt and relieved that WE weren’t the ones falling. ( Chevy did suffer a back injury doing those pratfalls, but that’s another thread ).
How’d I do? Make any sense at all?
Cartooniverse ( who only picked on Billdo and CajunMan out of affection ! )
Each addresses some aspect of your OP.
A
Oh and **Toonie[b/], thanks for the laugh.
Arrrrrghhhh!!
Sorry about the coding mess.