Laughter

Laughter is, basically, a social activity.  Humans laugh as a way to bond with each other -or to separate from those who belong to another social group. Other animal species also laugh, rats or apes, but the reasons why humans laugh are many and very nuanced.  This BBC article describes laughter and explains some of the reasons why we laugh.
Although the vocabulary in this article is very rich, the text can be accessible to B2 learners.