In French, the word ‘spirituel’ has two meanings: spiritual, and witty or humorous. In Italian the word for witty or humorous is similar: ‘spiritoso’. And likewise the German word ‘Geist’ has both meanings: spirit and wit. All those people can't be wrong! There must be a connection between spirituality and humour.
A humourless person is a danger to the public as well as to him or herself. It is said that “whom the gods would make bigots, they first deprive of humour.” Of course there is a cruel kind of humour (found even in children) that should not be classed as humour at all but as cruelty. What is humour? It is a leap: you are being carried along on the even tracks of a logical story, when suddenly, on the play of a word or an image or whatever, you are hurled onto a different level of meaning. It is the unexpectedness of it that shakes you up. Humour is the proof that someone around here is alive, that all isn't predictable matter and beaten tracks; that there is a living spirit present. See what it does to an atmosphere: everyone wakes up and makes strange illogical noises in their throats and looks extremely joyful for a moment: we call it laughter. Even the highest of the other animals don’t make these leaps; they can look very pleased at times, but they never make jokes. Humour is a distinctly human kind of leap. It is a leap of intelligence: chimpanzees leap from branch to branch, but we alone can see different levels of meaning and leap from one to another. Someone lacking humour may indeed by intelligent, but there is something mechanical and inhuman about such intelligence. I have not heard that computers make jokes either.
I lived for a few years in a country where people seemed to put humour in a special compartment, all by itself. It was permissible on certain occasions to produce a specimen from that box and exhibit it, at which everyone would laugh in concert for the correct duration, before returning to the “serious” business of life. To the rest of us this is worse than no humour at all. Humour should be like yeast, leavening the whole lump of soggy dough, making air bubbles and lightness everywhere. Deadly seriousness can be a form of anxiety, a desperate clinging to the self and to the objects of its attachment. It is often just plain insecurity and fear. Frightened children don’t leap, they stay stock still.
Don’t measure humour by the amount of laughter you hear. Laughter may be many things besides humorous; it may be cruel, cynical, bitter, taunting, nervous, crude, morbid, or plain mad. But there is a distinctive joy in pure humour. Laughter won't tell you, but the eyes will; like joy, like intelligence, humour is visible in the eyes.
I drew your attention to the French, Italian, and German words; but we didn’t look at the English word ‘humour’. It is related to ‘humid’ (the “bodily humours” were body fluids). So English suggests that humour is fluid - able to flow. (Yes, we do speak of ‘dry wit’; that's a special concoction, and it is dry in the sense that a Martini is dry.) Humour is able to flow, it is not rock solid. It doesn’t see everything as hard and solitary and deadly serious, like a corpse. It is evidence of spirit, a spirit that gives life.