The following list is by Robert Provine, author of Laughter: A Scientific Investigation

  1. Laughter is an instinctive behavior, produced and recognized by people of all cultures.
  2. Most laughter is not about humor; it’s about relationships between people. We are 30 more times likely to laugh in a social situation than when we are alone (without the presence of TV, books, radio).
  3. Laughter usually follows comments in conversation rather than intentional jokes.
  4. The speaker tends to laugh more than the audience.
  5. In groups, women laugh more than men. Women also laugh more at men more than men laugh at women.
  6. Laughter tends to occur in short bursts of vowel-like sounds such as “ha-ha,”, “ho-ho” or “he-he” which are repeated every fifth of a second.
  7. Most people can’t laugh on command. Laughter is not something we produce consciously.
  8. Laughter is contagious. The sounds of laughter often trigger laughter.
  9. Laughter is believed to have its origins in rough and tumble play, evolving from the panting behavior of our primate ancestors (when tickled, chimpanzees and gorillas pant).
  10. Laughter usually doesn’t interrupt a sentence structure of speech. We really only laugh during the pauses we make for coughing or breathing.