Behavior: The Mystery of Laughter

In the second month, the normal human infant breaks into its first smile. The expression is often considered a reflex action, but it soon becomes social, and in the fourth month develops into that explosive, exclusively human breath pattern called laughter. Laughter serves man well. It can relieve his anxiety and tension, pave the way to friendship and enable him to tolerate his own—and life's—absurdities. Laughter is vital in helping to define what is human: its absence is generally taken as a sign of grave psychic stress. Yet laughter itself has never been...

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