Polyandry is a marital arrangement in which a woman has several husbands. In Tibet, those husbands are often brothers; "fraternal polyandry". Concern over which children are fathered by which brother falls on the wife alone. She may or may not say who the father is because she does not wish to create conflict in the family or is unsure who the biological father is. Historically the social system compelled marriage within a social class.