Where Two or More Brothers Are Married to The Same Wife

Monogamy is probably the most common system of marriage throughout the world; it involves one man married to one woman. Polygyny, however, is the marriage of one man to more than one woman (like some Mormon sects), and polyandry, is the marriage of one woman to more than one man.
Fraternal polyandry is the most common type of polyandry. This is a type of marriage in which several brothers share one wife. This social practice has, and still sometimes does, occur in certain villages in Tibet, Nepal, and Northern India.

The custom of fraternal polyandry is believed to have come about as a way to make the inheritance of property easier and to prevent the break up of plots of land into smaller portions, by preserving large parcels of land. In doing this, families have a means to maintain resources, wealth and social standing, by a group of fathers passing a farm to a group of sons. If the farm was divided between all the sons, the land would become smaller and smaller and poverty would be the result.

The South American Yanomamö people who live in the Amazon Rainforest along the borders of Venezuela and Brazil practice polyandry as well as monogamy and polygyny. 

In the Himalayan regions of Tibet and Nepal, Fraternal polyandry is a solution to the lack of land available to some of these communities. Here a woman's husbands, who are usually brothers, will share the wife and the property and also share the children, with each brother being expected to treat all the offspring of the marriage as his own. 

In India, fraternal polyandry exists among various groups like the Khasa of Dehradun. Non-fraternal polyandry exists among some other groups, like the Kota people of the Nilgiri Hills in South India. In this society, a man’s brothers are free to have sexual relations with his wife, and when the husband is ill or incapacitated, or in any way unable to fulfil his duties as a husband, his brothers take his place. Basically, the brothers become secondary husbands.

If a husband from the Kota tribe is away overnight, he will appoint one of his brothers to sleep with his wife so that sorcerers from a nearby tribe cannot take advantage of the lone woman. Husbands from this tribe also learn not to be jealous of the relationship between their brothers and their wife.