The average four-year-old laughs 300 times a day, a 40-year-old, only four.
Humor is serious business. Sure, there's simple comedy like a pie in the face or an Adam Sandler movie, but a lot of jokes display real intellect, and despite much reflection and experimentation—both in labs and on stages—no one has yet discovered a unified theory of hilarity.
Laughter serves weightier purposes than turning noses into milk spigots. More than merely a side-effect of mirth, it acts as a sophisticated social signaling system, helping people bond and even negotiate status.