An Orangutan laughing
While our reasons for laughing can be more complex than our primate cousins, studying the laughter of these other species can give us insight as to why a hominid would laugh in the first place. These studies have shown that laughter is a social tool, used to communicate and express feelings to others. For example, chimpanzees will use "play pants" (inhaling and exhaling rapidly which is their form of laughter but almost sound like screeches to us) when tickled or playing with a mate to encourage the action. While laughter is not necessary for our survival as a species, its very important in building a community, connecting with other people, and giving us a way to better understand the world. When searching Google for images about the evolution of laughter, I came across this Calvin and Hobbes comic which I think summarizes a lot of my thinking about laughter and why it came about in the first place.
There are actually two types of laughs that humans express: Duchenne and non-Duchenne laughter. Duchenne laughter is a genuine laugh at something funny and used by our ancestors at times when they felt safe from predators and could socialize. This was the first type of laughter which scientists think our human ancestors started to develop 2 to 4 million years ago. The more complex non-Duchenne laughter is thought to have developed a couple hundred thousand years later. This laughter is not dependent on something actually being funny, but is a response that's purpose is to manipulate others in "aggressive, nervous, or hierarchical context, functioning to signal, to appease, to manipulate, to deride or to subvert"(Gervais and Wilson, 2005). That quote is a bit complicated but it is explaining a type of laugh that we are guilty of doing everyday and its not that there is anything wrong that, its not just the genuine type of laughter when we really find something funny. We do it in the midst of conversation even if something isn't that funny, even when we are simply greeting or saying goodbye to a friend. Its a mimic of Duchenne laughter to gain the effects that laughter gives which we can use to manipulate people in beneficial ways, or in some cases to take advantage of them. Using laughter in this way shows that this form of non-Duchenne laughter developed from humans with more complex behavior and cognitive abilities. Laughter has provided humans with a way to express joy to others without saying a word. It amazes me how long the use of laughing has come: from our early ancestors communicating to one another that it was alright to relax to people today telling jokes for the enjoyment of others.
Want to know more about the evolution of laughter and laughing in general? Check out these links:
Did Early Humans have a Sense of Humor?
Reconstructing the Evolution of Laughter in Humans and Great Apes
Our Primate Ancestors have been laughing for 10M years
How laughter works
Why do Humans Laugh
Gervais M, Wilson DS. 2005. The evolution and functions of laughter and humor: a synthetic approach. Q Rev Biol 80:395–430.