system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do humans laugh? How did it originate and for what purpose?

How did laughing develop among early hominids, and what purpose does it serve now, sociologically and biologically?
gpt
Chimps grin and snuffle as submissive expressions or when they're nervous. It's likely our ancestors had something similar going on, which over time became a response to humour, as opposed to tension. We still find awkwardness and tension very effective as components of humour, and the 'nervous laugh' is a trope for a reason. 

The response to tickling, for instance, is instinctive and submissive. It's a mock attack, and our first experience of it is generally at the hands of our big giant pack-leader parents. As we develop, it's a mock fight with familiar people; think of how you'd react if your girlfriend/boyfriend tickled you, and then think how you'd react if a stranger randomly started doing the same thing. Again here, laughter grows out of a defence/submission instinct. Being tickled is not, of itself, particularly funny. 

Much as words drift semantically, social mores can grow and develop. A shared response to tension becomes a more intimate expression of solidarity. That's why we find things funnier in groups, too. Think of how often you laugh at a funny TV show when on your own versus how often you'd laugh at the same show when watching it with friends.