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.
When the People's Republic of China annexed Tibet, political systems in many regions of Tibet remained unchanged until, between 1959 and 1960, political reforms changed the land ownership and taxation systems. Professor Melvyn Goldstein believed this affected Tibet's traditional marriage system. With the change in social stratification the du-jung and the mi-bo lower classes were the first to avoid the forms of marriage that characterized the older society.
However, as part of its population control measures, the Chinese government later forbade polyandrous marriage altogether under family law. Even though it is currently illegal, after collective farming was phased out and the farmed land reverted in the form of long-term leases to individual families, polyandry in Tibet is de facto the norm in rural areas.
Studies have attempted to explain the existence of polyandry in Tibet. One reason put forward in traditional literature is that by not allowing land to be split between brothers, Tibetan families retained farms sufficiently large to continue supporting their family. Another reason for polyandry is that the mountainous terrain makes some of the farm land difficult to farm, requiring more physical strength. Women take multiple husbands because they are strong and able to help tend their land.
The Tibetan social organization under Lhasa control from the 17th century on was quasi-feudal, in that arable land was divided and owned by families, religious organizations, and the central government and the population was subject to those district divisions. The population was further divided into social classes:
These wealthier family units hereditarily owned estates leased from their district authority, complete with land titles. In Goldstein's research about the Gyantse district specifically, he found them owning typically from 20 acres (81,000 m2) to 300 acres (1.2 km2) of land each. Their primary civil responsibility was to pay taxes (tre-ba and khral-pa means "taxpayer"), and to supply corvée services that included both human and animal labor to their district authority. According to Goldstein, the entire family structure and marriage system were subordinated to serve the land and corporate family unit.