Why Is That Funny? How evolution made us laugh.

Dunbar said this evolved originally as a form of chorusing. We took what had been just a, “Hey, do you want to play?” kind of vocalization between two individuals, to something being repeated endlessly between a group, one that’s perhaps sitting around a campfire. “It’s kind of like good old-fashioned round the campfire songs that everybody knows, because it doesn’t really matter what the words are,” Dunbar said. “We go through the motions of producing the words, but they become submerged and secondary to just the activity. It creates this sense of bonhomie, of belonging to a community.”

He thinks it evolved in that context because one of laughter’s hallmark signatures is its social spontaneity. “If somebody else laughs, it’s very difficult not to laugh with them. And if you get stuck in a conversation with good old Mr. Spock from Star Trek, bless him, who never smiled, never laughed, you’d go crazy. How do I get out of this? This is a terrible conversation that’s going on, because there’s no little jokes and one-liners being thrown about to make you smile and laugh,” Dunbar said. “So, laughter is important in our everyday conversations, and makes the conversation flow, in a very musical sense of flow. It has this same intimacy that social grooming has, in terms of creating these bonded relationships. And it does that by triggering this pressure on the diaphragm and the chest wall muscles when you empty the lungs, and stress the lungs, and then the musculature triggers the endorphin system just in the same way that grooming does, but better.”