A lot of common ideas about education, charity and laughter (we laugh because something is funny) are evolutionary useful lies we tell ourselves.
"But while we humans often play by ourselves (e.g., with Legos), recall that we laugh mostly in the presence of others. So what communicative purpose does laughter serve in the context of play? Gregory Bateson, a British anthropologist, figured it out during a trip to the zoo. He saw two monkeys engaged with each other in what looked like combat, but clearly wasn’t real. They were, in other words, merely play fighting. And what Bateson realized was that, in order to play fight, the monkeys needed some way to communicate their playful intentions—some way to convey the message, “We’re just playing.” Without one or more of these "play signals,” one monkey might misconstrue the other’s intentions, and their playful sparring could easily escalate into a real fight"