Why dose laughter seem to qualify as a biological function?

Laughter is part of the universal human vocabulary. All members of the human species understand it. Unlike English or French or Swahili, we don’t have to learn to speak it. We’re born with the capacity to laugh.

One of the remarkable things about laughter is that it occurs unconsciously. You don’t decide to do it. While we can consciously inhibit it, we don’t consciously produce laughter. That’s why it’s very hard to laugh on command or to fake laughter. (Don’t take my word for it: Ask a friend to laugh on the spot.)