I prefer to believe that, like the sense of beauty, the love of music, the thrill of admiration for uncalculating heroism, we have here a wondrous aid to us in our life's pilgrimage, but that if we trace it to a sense of our self-interest, we not only vulgarize it, but we turn it into a caricature. For there is in humour this singular property; its aroma is so subtle, delicate and undefinable that the effort to buttress it upon coarse, common utility is doomed to fail, and in the mere attempt humour vanishes. There is something deliciously contagious about laughter that is quite sincere and unthinking; whereas the only people who contrive to be always absurd, but never amusing, are those who laugh from a sense of duty.
Humour, then, in the young is restricted in scope, their experience of life being small; in women it is quicker than in men, but shallower; in the Scotch it is reticent, in the Irish voluble and refined, but cold. But wherever it is found free from counterfeit, wholesome and contagious, it is the offspring of man's heaven-bestowed power of seeing in the meannesses of earth the true presence of the Divine.
Darwin says the causes of humor are legion and exceedingly complex and various disquisitions upon humor and laughter would seem to support him. Its social nature is emphasized by Edwin Paxton Hood:
The sources of all laughter and merriment are in the cordial sympathies of our nature. Laughter is very nearly related to the highest and most instinctive wisdom; it stands at no distant remove from Judgment on the one hand, and Imagination on the other; and it is a proof of a healthy nature, for both thinking and acting.
C.S. Evans in his article "On Humor in Literature" gives a hint of the evolutionary process of its mechanism and its higher refinement:
On the lower plane of humor you get a laugh by the most unimaginative means--merely conceive a recognized humorous situation, or bring several things together according to a recipe, and the thing is done. Every practised comedian, in literature or on the stage, is an adept at it. But the creation of character, the expression--in terms of the words and actions of men and women--of that "social gesture" which is laughter's source, is a much greater thing, for there we touch the symbolism which is the soul of art.