Laughter is a form of social bonding because it is contagious and allows us to show that we are non-threatening.
We laugh when we see or hear something funny. We laugh to show that we are being silly.
Many anthropologists believe that language existed and evolved in the past few thousand years, but there is evidence suggesting that laughter arose from millions of years ago because we share the same structure of laughter with the great apes.
From a historical perspective it is ironic that tickling in the modern era is considered to be a way to bond for parents and their children because a few centuries back tickling was a form of punishment.
Thanks to evolution laughter became a way for people to enjoy each other's company without any danger or injuries.