Why do people laugh, you ask. The researchers' conclusion? As with almost all psychology today: Nature & Nurture. First the nature:
(Researchers have) discovered something that eluded Plato, Aristotle, Hobbes, Kant, Schopenhauer, Freud and the many theorists who have tried to explain laughter based on the mistaken premise that they’re explaining humor.
Of course. Evolutionary Psychology. What about nurture? Well, laughter is a way of climbing the social ladder. If we want to be accepted by people in our environment, we laugh at their jokes (Note: It's not a good idea to laugh at people we want to like us. Just their jokes.):
(Laughter is) an instinctual survival tool for social animals, not an intellectual response to wit. It’s not about getting the joke. It’s about getting along...It’s a kind of behavioral fossil showing the roots that all human beings, maybe all mammals, have in common...Primal laughter evolved as a signaling device to highlight readiness for friendly interaction
By the way, the research, you can note, is standard experimentation. Experimental and control groups. Lying to the subjects (Oh, wait, I'm sorry. It's not lying. It's using a cover story to ensure participant blindness [doesn't that sound much nicer than lying?]).
When you’re low in the status hierarchy, you need all the allies you can find, so apparently you’re primed to chuckle at anything even if it doesn’t do you any immediate good.
So that all explains why, at the beginning of the semester, students laugh at my stupid jokes. By the end, when they realize it has no impact on their grades, they've stopped. I need funnier jokes.
*Answer: One. But the light bulb has to really want to change.