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.
The Function of Humor
In an article entitled "Why Do We Laugh?" William McDougall discusses scientifically the value of laughter:
Laughter of man presents a problem with which philosophers have wrestled in all ages with little success. Man is the only animal that laughs. And, if laughter may properly be called an instinctive reaction, the instinct of laughter is the only one peculiar to the human species....
We are saved from this multitude of small sympathetic pains and depressions by laughter, which, as we have seen, breaks up our train of mental activity and prevents our dwelling upon the distressing situation, and which also provides an antidote to the depressing influence in the form of physiological stimulation that raises the blood-pressure and promotes the circulation of the blood. This, then, is the biological function of laughter, one of the most delicate and beautiful of all nature's adjustments. In order that man should reap the full benefits of life in the social group, it was necessary that his primitive sympathetic tendencies should be strong and delicately adjusted. For without this, there could be little mutual understanding, and only imperfect cooperation and mutual aid in the more serious difficulties and embarrassments of life. But, in endowing man with delicately responsive sympathetic tendencies, nature rendered him liable to suffer a thousand pains and depressions upon a thousand occasions of mishap to his fellows, occasions so trivial as to call for no effort of support or assistance. Here was a dilemma—whether to leave man so little sympathetic that he would be incapable of effective social life; or to render him effectively sympathetic and leave him subject to the perpetually renewed pains of sympathy, which, if not counteracted, would seriously depress his vitality and perhaps destroy the species. Nature, confronted with this problem, solved it by the invention of laughter. She endowed man with the instinct to laugh on contemplation of these minor mishaps of his fellow men; and so made them occasions of actual benefit to the beholder; all those things which, apart from laughter, would have been mildly displeasing and depressing, became objects and occasions of stimulating beneficial laughter....
For laughter is no exception to the law of primitive sympathy; but rather illustrates it most clearly and familiarly; the infectiousness of laughter is notorious and as irresistible as the infection of fear itself.... The great laugher is the person of delicately responsive sympathetic reactions; and his laughter quickly gives place to pity and comforting support, if our misfortune waxes more severe. Such persons are in little danger of giving offense by their laughter; for we detect their ready sympathy and easily laugh with them; they teach us to be humorous.
H. Merian Allen in his essay "Little Laughs in History" says "The relaxation of a full laugh clears the brain, restores fit contact with one's fellows, and so smoothes the way for the solving of knotty problems."
Linus W. Kline, Ph.D., further elucidates the psychical office of humor as follows:
The psychical function of humor is to delicately cut the surface tension of consciousness and disarrange its structure that it may begin again from a new and strengthened base. It permits our mental forces to reform under cover, as it were, while the battle is still on. Then, too, it clarifies the field and reveals the strategetic points, or, to change the figure, it pulls off the mask and exposes the real man. No stimulus, perhaps more mercifully and effectually breaks the surface tension of consciousness, thereby conditioning the mind for a stronger forward movement, than that of humor. It is the one universal dispensary for human kind: a medicine for the poor, a tonic for the rich, a recreation for the fatigued and a beneficient check to the strenuous. It acts as a shield to the reformer, as an entering wedge to the recluse and as a decoy for barter and trade.
Humor is as necessary to our mental and spiritual life as are vitamins to our physical well-being. Ruskin has called our attention to the tendency of rivers to lean a little to one side, to have "One shingly shore upon which they can be shallow and foolish and childlike, and another steep shore under which they can pause and purify themselves and get their strength of waves fully together for due occasions," and has likened them to great men who must have one side of their life for work and another for play. Action and reaction must be balanced: seriousness and lightness. "Men who work prodigously must play with equal energy," says one commentator. "Humor is the gift of the deeply serious man," remarks another. "There have been very few solemn men, but their solemnity was evidence, not of their gifts, but of their defects; as a rule greatness is accompanied by the overflow of the fountain of life in play." "The richly furnished mind overflows with vitality and deals with ideas and life freely, daringly, often audaciously."