Topics: Polygamy - Wikipedia
Of the 1,231 societies listed in the 1980 Ethnographic Atlas, 186 were found to be monogamous; 453 had occasional polygyny; 588 had more frequent polygyny; and 4 had polyandry.  Polyandry is less rare than this figure which listed only those examples found in the Himalayan mountains (28 societies). More recent studies have found more than 50 other societies practicing polyandry. 
Fraternal polyandry was traditionally practiced among Tibetans in Nepal , parts of China and part of northern India, in which two or more brothers are married to the same wife, with the wife having equal "sexual access" to them.  It is associated with partible paternity , the cultural belief that a child can have more than one father. 
In the Indian Himalayas, polyandry may be combined with polygyny to produce a system termed "polygynandry". The system results in less land fragmentation, a diversification of domestic economic activities, and lower population growth.