Many scientists believe laughter is a primitive expression of relief after a moment of danger has passed or a mental uncertainty is resolved. I picture a group of cavemen developing history’s first chuckle after evading a Sabertoothed Tiger.

Perhaps a better example can be found in the anatomy of humor itself. A joke creates a brief inconsistency (or uncertainty) in your mind–then you say “Oh, I get it” and have a good laugh.

I don’t know whether this evolution-based theory is true. How does it explain the people in this video? If anything, these mutant laughers could scare away predators.