Pretend you’re a caveman traveling with your hunting party. Your friend, Ugg, trips on the only banana peel, rock, or twig for miles, falling flat on his face. He’s then abruptly eaten by a tiger. His DNA line grinds to a halt, and worse still, he has endangered the hunting party which now has less man-power, and an angry tiger to contend with. You and your other hunting mates are now in mortal danger. There is nothing funny about this.
Once again pretend that Ugg trips and falls on that same banana peel, falling into a pool of mud, but emerges safely (though still covered in mud). What do the other caveman do this time? They erupt into laughter, at Ugg. Ugg is shamed by this, and makes extra effort to watch where he steps. Ugg is more careful, and less of a liability.
The caveman that laughed together have established what is acceptable by laughing at what is to be avoided.
We laugh when we spot something that’s ridiculous, out of place, ironic, or contradictory. We do this to signal to our peers that we “get what’s odd”, that we are at least as smart as they are, and that we aren’t a threat to group survival. (Heck, we’re even willing to fake laughter even when we don’t get it, to avoid being the ‘odd-man' out!)
We feel closer to those we laugh with, and we distance ourselves from those we can’t laugh with. (Some of our best memories are laughing with friends, and the worst are when we are ridiculed so others may laugh. I think this also explains why woman find humor so attractive; after a woman assesses a man for looks, this is how she assesses intelligence)
Laughter is an instinctual behavior that strengthens bonds between like minded individuals, and weakens ties with others.
So keep your wits (synonym for smarts) sharp, your social status (and survival) depends on it.