The reasons we laugh, including ‘contagious’ laughter, may be products of evolution. Natural laughter is a two-part, spontaneous, response to humor, that has physiological, psychological, and physical benefits. Most agree that we laugh when we find something to be humorous, though different reasons exist for what we find to be humorous. Additionally, different things are humorous to us at different stages of life.
Laughter, a physiological response to humor, can be broken down into two parts. The first is a set of gestures, and the second is the production of sound. The brain forces to conduct both responses simultaneously.
From a physiological standpoint, a ‘sensor’ in the brain responds to laughter by triggering other neural circuits in the brain, which, in turn, generate more laughter. Oddly enough, laughter is an orderly response, and almost occurs spontaneously during pauses at the end of phrases, earning it the name the ‘punctuation effect’. Human beings are the only species capable of laughter, and an average adult does so approximately 17 times per day.
Scientists say that laughing is a great exercise and estimates that laughing 100 times is equivalent to a 10-minute workout on a rowing machine, or 15 minutes on a stationary exercise bike.