Why Do We Laugh? – Scientific American

Laughter clearly serves a social function. It is a way for us to signal to another person that we wish to connect with them. In fact, in a study of thousands of examples of laughter, the speakers in a conversation were found to be 46 percent more likely to laugh than the listeners.
We’re also 30 times more likely to laugh in a group. Young children between the ages of 2.5 and 4 were found to be eight times more likely to laugh at a cartoon when they watched it with another child even though they were just as likely to report that the cartoon was funny whether alone or not. 
— Read on www.scientificamerican.com/article/why-do-we-laugh/