Good question! Laughter is involuntary and it always happens as a reaction to something…in a way, its evolutionary significance comes from the fact that it is one of the essential mechanisms for socializing. By laughing you are basically expressing your emotions without speaking, but everyone will understand what you mean (if is of fun or making fun of, maybe just a panic laughter, or even to be sarcastic!) and is a universal language! Also you laugh since you are born so it is innate to us, and it helps the parents understand if all is good with the baby….from that point on, the baby understands (even if not consciously) that by laughing it is communicating. It is also really connection to our emotions, and in the brain it is related to both the hippocampus and the amygdala, as well as the production of endorfins that make you happy! So, from communication to expression of feelings, laughing is innate to humans and essential for social interaction!