Laughing and crying are normally considered as indicating states of positive and negative valence. I view their evocation as being indicative of, and instrumental in, the modulation of the states of fear and aggressiveness respectively. Laughter as an exapted displacement activity: the implications for humor theory. It seems that I am unable to post a URL, but those who are particularly interested can find it by Googling: basilhughhall *** Mod Note*** This is the link.
I haven't read the full document yet, but I will say this: it's hardly a new idea. Larry Niven loosely described laughter as the result of an "interrupted defence mechanism" in his science fiction novel Ringworld in 1970.
