It is apparently an immediate effect of the recognition of the incongruous, just as trembling is of the recognition of danger.

It may have been evolved because an animal which suffered a slight spasm in the presence of the unexpected was more likely to be on its guard against enemies, or it may have been the merely accidental result of some fact in our nervous organisation which was otherwise useful.

Incongruity is, however, so much a matter of habit and association and individual variation, that it is extraordinarily difficult to forecast whether any particular act will seem ridiculous to any particular class, or how long the sense of incongruity will in any case persist.

Acts, for instance, which aim at producing exalted emotional effect among ordinary slow-witted people--Burke's dagger, Louis Napoleon's tame eagle, the German Kaiser's telegrams about Huns and mailed fists--may do so, and therefore be in the end politically successful, although they produce spontaneous laughter in men whose conception of good political manners is based upon the idea of self-restraint.
Again, almost the whole of the economic question between socialism and individualism turns on the nature and limitations of the desire for property.

There seem to be good grounds for supposing that this is a true specific instinct, and not merely the result of habit or of the intellectual choice of means for satisfying the desire of power.
Children, for instance, quarrel furiously at a very early age over apparently worthless things, and collect and hide them long before they can have any clear notion of the advantages to be derived from individual possession.