Exchange marriage
Exchange marriage is a form of marriage involving an arranged and reciprocal exchange of spouses between two groups. In this tradition, a pair consisting of brother and sister are married from one family to another pair of another family. When the process is repeated for generations then it is called cousin marriage.
It is common among the some Australian Aborigines and American Subarctic peoples.
In Pakistan, it is called watta satta, and about a third of all marriages in rural Pakistan are on this basis.
