The original post: /r/todayilearned by /u/0---------------0 on 2024-12-01 21:31:09.

Original Title: TIL of Sister Exchange, a type of marriage agreement where two sets of siblings marry each other. In order to get married, a man needs to persuade his sister to marry the bride’s brother. It is practised as a primary method of organising marriages in 3% of the world’s societies.