Laughter is very much related to the emotion of fear and uneasiness. The classic act of a man tripping over a banana skin involves the danger of physical injury. The false-alarm theory postulates that laughter has evolved as a mechanism to reassure one's mates when a possibly menacing situation has dissolved. The banana skin act is comic because it hinges upon physical vulnerability, while not being actually damaging.
One is captured by an urge to burst into laughter when one is inherently fearful or uneasy. I vividly remember an example from my own childhood. When I was in the second grade of elementary school, suddenly a "milk scare" seized us boys. This was nothing serious for the health. It was a comic scare.
I don't exactly recall who started it, but I can testify that before knowing it, I was one of the active protagonists. We were served with school meals during lunch time. The idea was to say funny things or make comic gestures while somebody was drinking milk from the bottle. The victim would burst into laughter, and squirt the milk into the air. I remember a particularly effective operation when one of my best friends literally became a white fountain. After the incident, there were stains of white liquids all over. Some of them were on our faces and hands. We the brats shouted merrily in the aftermath, and bursted into peals of laughter.
Although the whole thing was done in good spirits, we were literally scared all the same. Fearing that somebody would make you laugh, you drank up the milk as soon as it was delivered. The enormous peer pressure in the form of forced milk drinking is still clear in my memory. Looking back, I think the milk scare taught me the essence of the origin of laughter, long before I came across any scientific theories of mirth.
When we became third graders, the manner in which the school meal milk was delivered was changed. The milk now came in a "Tetra Pak", with a straw attached. Drinking milk then changed from a savage gulping to a gracious sipping. The days of our milk scare were over, much to our regret and relief, although we would never admit to the relief part before our fellow brats.