Hence Asimov's positronic brain? Topical if not hilarious - I submit.

What is a joke? Yes I crack jokes all the time. I even invent them - but, you know, some upstart inventers got there before me all too often. - And when they didn't? Well only because no one told me. But the laws of probability are such that my best chance of that is getting to a new meaning first.

Context is all in humour. The joke before, the joke after, the precise words relative to the lexicon of the listener. Hey this is a serious business - being funny.

Frued reckoned that a joke was as effective as a glass of sherry in the conviviality stakes so, contrary to popular Viennese middle class society mores, he delivered a joke as friends entered Chateau Frued instead of booze. Having seen one of his jokes I feel he worked at it too hard - & he was no natural. However "drunk with laughter" is a phrase that comes from somewhere.

I usually reckon that jokes rely on duality, stout pomous party, the banana skin the collapse; the duality of "him (thank goodness) not me (ouch)"; the duality of predicted scenario, all change, rethink. And the duality of jokes that don't fit that mould. Gerrard Hoffnung, most well known source story of "Paddy's Sick note (etc etc)" - we all can work out what is coming next but still laugh- except that the twists and turns are so numerous and well thought-out we don't spot them all - the duality of surprise. In the split second we see the new meaning/situation we carry conflict in our heads which is a puzzle which we solve and feel good about ourselves. Humour stereo-types have men as better joke-tellers but then men are by nature problem solvers first, women more likely visit their feelings first - hence the skew in male jokers/comedians. (Disclaimer - this is a statistical artefact not a person by person value judgement :)

In the social context humour has a very demonstrable benefit (and evolutionary function I am sure) in that it binds a society. You can't stay mad at people if you are laughing with a common target. Tribes and families need that at times. And we are very much a herding pair-bonding species. It is very definitely NATURE though I will acknowledge it can be nutured in most people.