“Laughter is an honest social signal because it’s hard to fake,” Professor Provine says. “We’re dealing with something powerful, ancient and crude. It’s a kind of behavioral fossil showing the roots that all human beings, maybe all mammals, have in common.”What's So Funny? Well, Maybe Nothing (John Tierney, New York Times, March 13, 2007)
The human ha-ha evolved from the rhythmic sound — pant-pant — made by primates like chimpanzees when they tickle and chase one other while playing. Jaak Panksepp, a neuroscientist and psychologist at Washington State University, discovered that rats emit an ultrasonic chirp (inaudible to humans without special equipment) when they’re tickled, and they like the sensation so much they keep coming back for more tickling.
He and Professor Provine figure that the first primate joke — that is, the first action to produce a laugh without physical contact — was the feigned tickle, the same kind of coo-chi-coo move parents make when they thrust their wiggling fingers at a baby. Professor Panksepp thinks the brain has ancient wiring to produce laughter so that young animals learn to play with one another. The laughter stimulates euphoria circuits in the brain and also reassures the other animals that they’re playing, not fighting.
“Primal laughter evolved as a signaling device to highlight readiness for friendly interaction,” Professor Panksepp says. “Sophisticated social animals such as mammals need an emotionally positive mechanism to help create social brains and to weave organisms effectively into the social fabric.”
When the going gets weird, the weird turn pro. - Hunter S. Thompson