Exogamy

Exogamy is a social arrangement where marriage is allowed only outside a social group. The social groups define the scope and extent of exogamy, and the rules and enforcement mechanisms that ensure its continuity. In social studies, exogamy is viewed as a combination of two related aspects: biological and cultural. Biological exogamy is marriage of nonblood-related beings, regulated by forms of incest law. A form of exogamy is dual exogamy, in which two groups engage in continual wife exchange. Cultural exogamy is marrying outside a specific cultural group; the opposite being endogamy, marriage within a social group.

In biology, exogamy more generally refers to the mating of individuals who are relatively less related genetically: that is, outbreeding as opposed to inbreeding. This benefits the offspring as it reduces the risk of the offspring inheriting two copies of a defective gene. Increasing the genetic diversity of the offspring is thought to improve their chances of surviving to reproduce themselves.

Scientists surmise that the drive in humans, as in many animals, to engage in exogamy (outbreeding) 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 recessive gene. The genetic principles involved apply to all species, not just humans.

Individuals who breed with more 'exotic' (or distant) partners and avoid incestuous relationships tend to have healthier offspring, due to the benefits of heterosis. Maladapative genetic conditions are more likely to be inherited where inbreeding takes place, or within relatively closed populations over long periods of time. An example is cystic fibrosis, which has developed as a genetic disease inherited chiefly by people of European descent. Another genetic disease specific to certain populations is sickle-cell anemia, for which people of African descent are more at risk; it developed among Africans together with higher immunity to malaria, which is endemic on the continent. Offspring may not always inherit such adaptations that evolved in specific geographic areas. Genetic concerns are not the only cause for exogamy; many social and political aspects support this system of marriage, throughout societies and species.

Cultural exogamy is the custom of marrying outside a specified group of people to which a person belongs. Thus, persons may be expected to marry outside their totem clan(s) or other groups, in addition to outside closer blood relatives.

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