Why we laugh?

"So this suggests strongly it's hard-wired in the brain and this raises an interesting question. Why did it evolve in the brain, OK, how did it evolve through natural selection? When you look at all jokes and humour across societies, the common denominator of all jokes and humour despite all the diversity is that you take a person along a garden path of expectation and at the very end you suddenly introduce au unexpected twist that entails a complete re-interpretation of all the previous facts. That's called a punch-line of the joke. Now obviously that is not sufficient for laughter because then every great scientific discovery or every "paradigm shift" would be funny, and my scientific colleagues wouldn't find it amusing if I said their discoveries were funny.

OK, the key ingredient here is, it's not merely sufficient that you introduce a re-interpretation but the re-interpretation, the new model you have come up with should be inconsequential, it should be of trivial consequence. It sounds a bit abstract so let me illustrate with a concrete example. Here is a portly gentleman walking along, he is trying to reach his destination, but before he does that he slips on a banana peel and falls. And then he breaks his head and blood spills out and obviously you are not going to laugh. You are going to rush to the telephone and call the ambulance. But imagine instead of that, he walks along, slips on the banana peel, falls, wipes off the goo from his face, looks around him everywhere, and and then gets up, then you start laughing. The reason is I claim is because now you know it's inconsequential, you say, oh it's no big deal, there's no real danger here. So what I'm arguing is, laughter is nature's false alarm. Why is this useful from an evolutionary standpoint? So what you are doing with this rhythmic stocatto sound of laughter is informing your kin who share your genes, don't waste your precious resources rushing to this person's aid, it's a false alarm everything is OK. OK, so it's nature's OK signal."

Picked from Reith Lectures 2003 on Emerging Mind by V S Ramachandran, world renowned brain scientist

They are available (both text/audio clips):
http://www.bbc.co.uk/radio4/reith2003/lectures.shtml