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Group marriageis a non-monogamous marriage-like arrangement where three or more adults live together, all considering themselves partners, sharing finances, children, and household responsibilities. Group marriage is considered a form of polyamory. The term does not refer to bigamy as no claim to being married in formal legal terms is made.
The concept reentered popular consciousness in 1974 with the publication of Group Marriage: a study of contemporary multilateral marriage by Larry Constantine and Joan Constantine.
Depending on the sexual orientation and activity of the members, all adults in the family may be sexual partners. For instance, if all members are heterosexual, all the women may have sexual relationships with all the men. If members are bisexual or pansexual, they may have evolved sexual relationships with either sex.
Group marriage implies a strong commitment to be faithful[when defined as?] by only having sex within the group and staying together longterm. The group may be open to taking on new partners, but only if all members of the family agree to accept the new person as a partner. The new person then moves into the household and becomes an equal member of the family.
Currently,[when?] the most common form of group marriage is a triad of two women and one man, or two men and one woman.[better source needed] There are also polyfidelitous families formed by two heterosexual couples who become a foursome and live together as a family.
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In most countries, it is not explicitly illegal for three or more people to form and share a sexual relationship (subject sometimes to laws against homosexuality), though such relational forms risk running afoul of state or local ordinances banning unmarried cohabitation. No Western country permits statutory marriage between more than two people. Nor do they give strong and equal legal protection (e.g., of rights relating to children) to non-married partners — the legal regime is not comparable to that applied to married couples. Individuals involved in polyamorous relationships are considered by the law to be no different from people who live together or date under other circumstances.
- Among the Ancient Hawaiians, the relationship of punalua involved "the fact that two or more brothers with their wives, or two or more sisters with their husbands, were inclined to possess each other in common". Friedrich Ratzel in The History of Mankind reported in 1896 that in Hawaii a kind of incipient polyandry arose by the addition to the marriage establishment of a cicisbeo, known as Punalua.
- In some parts of Melanesia, there are "sexual relations between a group of men formed by the husband's brothers and a group of women formed by the wife's sisters".
- Women of Nair community, a caste in Kerala, India, used to practice polyandry.
- Toda people, who live on the isolated Nilgiri plateau of Southern India practiced adelphic polyandry for centuries, but no longer do so. Adelphic polyandry occurs when brothers share the same wife or wives. Such arrangements have been common in Himalayan tribes until recently.
- In Sri Lanka, Sinhalese people practiced adelphic polyandry in the past, but no longer it is common to do so. The main motive behind this is to protect the wealth undivided. If there were seven or less brothers in a family, younger brothers get acces to the eldest brother's wife. For families with more than seven brothers, the eighth brother will marry a new bride. younger brothers get access to the eighth brothers wife, but not the elder brothers. 
The following instances are cited in Thomas 1906.
- In North America there is "group marriage as existing among the Omahas … adelphic polygyny."
- Among the Dieri of Australia exist forms of spouse-sharing known as pirrauru, in two categories "according to whether or not the man has or has not a tippa-malku wife. In the first case it is, taken in combination with the tippa-malku marriage, a case of bilateral dissimilar adelphic (M. and F.) polygamy. In the latter case it is dissimilar adelphic (tribal) polyandry". The pirrauru "relation arises through the exchange by brothers of their wives".
- Among the Kurnandaburi of Australia, "a group of men who are own or tribal brothers are united … in group marriage".
- Among the Wakelbura of Australia, there is "adelphic polyandry."
- Among the Kurnai of Australia, "unmarried men have access to their brothers' wives."
In modern U.S. practicesEdit
Group marriage occasionally occurred in communal societies founded in the 19th and 20th centuries.
A long-lived example was the Oneida Community founded by John Humphrey Noyes in 1848. Noyes taught that he and his followers, having reached 200 in number, had thus undergone sanctification; that is, it was impossible for them to sin, and that for the sanctified, marriage (along with private property) was abolished as an expression of jealousy and exclusiveness. The Oneida commune lived together as a single large group and shared parental responsibilities. Any given male-female combination in the group was free to have sex, usually upon the man's asking the woman, and this was the common practice for many years. The group began to falter about 1879–1881, eventually disbanding after Noyes fled arrest. Several dozen pairs of Oneidans quickly married in traditional fashion.
It is difficult to estimate the number of people who actually practice group marriage in modern societies, as such a form of marriage is not officially recognized or permitted in any jurisdiction in the U.S., and de jure illegal in many. It is also not always visible when people sharing a residence consider themselves privately to be a group marriage.
Portrayal in literatureEdit
Group marriage has been a literary theme, particularly in science fiction, and especially in the later novels of Robert A. Heinlein such as Stranger in a Strange Land, Friday, Time Enough for Love, and The Moon Is a Harsh Mistress. Stranger in a Strange Land describes a communal group much like the Oneida Society. In at least The Moon Is a Harsh Mistress and Friday it is called "line marriage".
In several of her Hainish Cycle stories, Ursula Le Guin describes a type of four-person marriage known as a sedoretu, practiced on the planet O. In this arrangement, two men and two women are married to each other, but each member of the marriage has a sexual relationship only with one male and one female spouse.
- "Models of Open Relationships by Kathy Labriola". Cat-and-dragon.com. Retrieved 2015-12-22.
- Westermarck 1922, Part III, p. 240
- Ratzel, Friedrich (1896). The History of Mankind. London: MacMillan Press. p. 277. Retrieved 11 April 2010.
- Westermarck 1922, Part III, p. 241
- Mathew, Biju. "Nair Polyandry". Kerala. Archived from the original on 2018-06-18. Retrieved 2018-06-18.
- Polgreen, Lydia (16 July 2010). "One Bride for 2 Brothers: A Custom Fades in India". The New York Times. Malang, India.
- සේනාරත්න,පී.ඇම්.ශ්රී ලංකාවේ විවාහ චාරිත්ර,සීමාසහිත ඇම්.ඩී.ගුණසේන සහ සමාගම,කොළඹ,1999.
- Northcote W. Thomas (1906). Kinship Organizations and Group Marriage in Australia. Cambridge: Cambridge University Press.
- Le Guin, Ursula (2002). The Birthday of the World and Other Stories. HarperCollins.
- Constantine, Larry and Joan (1974). Group Marriage: A Study of Contemporary Multilateral Marriage. Collier Books. ISBN 978-0020759102.
- Dillard, J.M. (1990). The Lost Years. Pocket Books. p. 440. ISBN 978-0-6717-0795-8.
- Emens, Elizabeth F. (2004). "Monogamy's Law: Compulsory Monogamy and Polyamorous Existence". New York University Review of Law & Social Change. 29 (2): 277.
- Heinlein, Robert (1996). The Moon Is a Harsh Mistress. Tom Doherty Associates, Inc. ISBN 978-0-3128-6176-6.
- Murdock, George P. (1949). Social Structure. New York: The MacMillan Company. ISBN 0-02-922290-7.
- Murdock, George P. "Ethnographic Atlas Codebook", derived from Ethnographic Atlas
- Westermarck, Edward (1922). The History of Human Marriage. New York: Allerton Book Company.