Today's Moment of Science: Laughter is a Social Signal?
Laughter research has found that only a small percentage of laughter, less than 20%, is a sincere response to someone's humor. In fact, laughter is primarily a social signal, as opposed to an emotional outburst. People are thirty times more likely to laugh in a social situation than when they are alone. And other observations about laughter also imply it has a social function. For instance, there's "polite" laughter. How often have you found yourself laughing at someone's attempt at being funny in order to spare their feelings or make them feel good?
Research has also found that women tend to laugh a good deal more than men. And male speakers tend to illicit more laughter than female speakers. Also, laughter may very well be a sign of power dynamics between people, signaling dominance and submission, acceptance and rejection. Certainly, that seems to be the case when someone is laughed at rather than with.