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Exogamy is thesocial norm of mating or marrying outside one'ssocial group. The group defines the scope and extent of exogamy, and the rules and enforcement mechanisms that ensure its continuity. One form of exogamy isdual exogamy, in which two groups continually intermarry with each other.[1]
Insocial science, exogamy is viewed as a combination of two related aspects: biological and cultural. Biological exogamy is the marriage of people who are notblood relatives. This is regulated byincest taboos andlaws against incest. Cultural exogamy is marrying outside a specific cultural group; the opposite beingendogamy, marriage within a social group.
Exogamy often results in two individuals that are not closely genetically related marrying each other; that is,outbreeding as opposed toinbreeding. This may benefit offspring as it reduces the risk of the offspring inheriting two copies of a defective gene. Nancy Wilmsen Thornhill states that the drive in humans to not reproduce or be attracted to one's immediate family is evolutionarily adaptive, as it reduces the risk of children having genetic defects caused by inbreeding, as a result of inheriting two copies of a deleterious recessive gene.[2]
In oneOld Order Amish society, inbreeding increases the risk of "neonatal and postneonatal mortality."[3] In French populations, the children of first cousins developcystinosis at a greater rate than the general population.[4]
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Cultural exogamy is the custom ofmarrying outside a specified group of people to which a person belongs. Thus, persons may be expected to marry outside theirtotem clan(s) or other groups, in addition to outside closer blood relatives.
Researchers have proposed different theories to account for the origin of exogamy.Edvard Westermarck said an aversion to marriage between blood relatives or nearkin emerged with a parental deterrence ofincest. From a genetic point of view, aversion to breeding with close relatives results in fewer congenital diseases. If one person has a faulty gene, breeding outside his group increases the chances that his partner will have another functional type gene and their child may not suffer the defect. Outbreeding favours the condition ofheterozygosity, that is having two nonidentical copies of a given gene.J. F. McLennan[5] holds that exogamy was due originally to a scarcity of women among small bands. Men were obliged to seek wives from other groups, includingmarriage by capture, and exogamy developed as a cultural custom.
Émile Durkheim[6] derives exogamy fromtotemism. He said that a people had religious respect for the blood of a totemic clan, for the clan totem is a god and is present especially in the blood, a sacred substance.
In some forms ofHinduism such asShaktism, people can only marry outside theirgotra which is a traditional group of people who may be distantly related but have been living in the same area or have an ancestral home in the same area.
Morgan[7] maintains that exogamy was introduced to prevent marriage between blood relations, especially between brother and sister, which had been common in an earlier state of promiscuity. Frazer[8] says that exogamy was begun to maintain the survival of family groups, especially when single families became larger political groups.
Claude Lévi-Strauss introduced the "Alliance Theory" of exogamy,[9] that is, that small groups must force their members to marry outside so as to build alliances with other groups. According to this theory, groups that engaged in exogamy would flourish, while those that did not would all die, either literally or because they lacked sufficient ties for cultural and economic exchange, leaving them at a disadvantage. The exchange of men or women served as a uniting force between groups.
Dual exogamy, in which two groups continually intermarry with each other, is a traditional form of arranging marriages in numerous modern societies and in many societies described in classical literature. It can be matrilineal or patrilineal. It is practiced by someAustralian tribes,[10] historically widespread in theTurkic societies,[11][12] Taï societies (Ivory Coast),[13]Eskimo,[14] amongOb-Ugrians[15][16] and others. In tribal societies, the dual exogamy union lasted for many generations, ultimately uniting the groups initially unrelated by blood or language into a single tribe or nation.
Linguistic exogamy is a form of cultural exogamy in which marriage occurs between speakers of different languages. The custom is common among indigenous groups in the northwestAmazon, such as theTucano tribes.[17]
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