Exogamy

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Exogamy is the social norm of mating or marrying outside one's social group. The group defines the scope and extent of exogamy, and the rules and enforcement mechanisms that ensure its continuity. One form of exogamy is dual exogamy, in which two groups continually intermarry with each other. [1]

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In social science, exogamy is viewed as a combination of two related aspects: biological and cultural. Biological exogamy is the marriage of people who are not blood relatives. This is regulated by incest taboos and laws against incest. Cultural exogamy is marrying outside a specific cultural group; the opposite being endogamy, marriage within a social group.

Biology of exogamy

Exogamy often results in two individuals that are not closely genetically related marrying each other; that is, outbreeding as opposed to inbreeding. In moderation, 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 improves the chances of offspring reproducing, up until the fourth-cousin level of relatedness; however, reproduction between individuals on the fourth-cousin level of relatedness decreases evolutionary fitness. [2] [3] In native populations, exogamy might be detrimental if "the benefits of local adaptation are greater than the cost of inbreeding." However, non-native, "invasive" populations that have "not yet established a pattern of local adaptation" may derive some adaptive benefit from admixture. [4]

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. [5]

In one Old Order Amish society, inbreeding increases the risk of "neonatal and postneonatal mortality." [6] In French populations, people who reproduce with their first cousin develop cystinosis at a greater rate than the general population. [7]

Cultural exogamy

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.

Researchers have proposed different theories to account for the origin of exogamy. Edvard Westermarck said an aversion to marriage between blood relatives or near kin emerged with a parental deterrence of incest. 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 of heterozygosity, that is having two nonidentical copies of a given gene. J. F. McLennan [8] holds that exogamy was due originally to a scarcity of women among small bands. Men were obliged to seek wives from other groups, including marriage by capture, and exogamy developed as a cultural custom.

Émile Durkheim [9] derives exogamy from totemism. 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 of Hinduism such as Shaktism, people can only marry outside their gotra 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 [10] 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 [11] 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, [12] 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

Dual exogamy 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 some Australian tribes, [13] historically widespread in the Turkic societies, [14] [15] Taï societies (Ivory Coast), [16] Eskimo, [17] among Ugrians [18] 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

Linguistic exogamy is a form of cultural exogamy in which marriage occurs only between speakers of different languages. The custom is common among indigenous groups in the northwest Amazon, such as the Tucano tribes. [19]

See also

Related Research Articles

Incest is human sexual activity between family members or close relatives. This typically includes sexual activity between people in consanguinity, and sometimes those related by affinity, adoption, or lineage. It is strictly forbidden and considered immoral in most societies, and can lead to an increased risk of genetic disorders in children.

<span class="mw-page-title-main">Inbreeding</span> Reproduction by closely related organisms

Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious recessive traits resulting from incestuous sexual relationships and consanguinity. Animals avoid incest only rarely.

An incest taboo is any cultural rule or norm that prohibits sexual relations between certain members of the same family, mainly between individuals related by blood. All human cultures have norms that exclude certain close relatives from those considered suitable or permissible sexual or marriage partners, making such relationships taboo. However, different norms exist among cultures as to which blood relations are permissible as sexual partners and which are not. Sexual relations between related persons which are subject to the taboo are called incestuous relationships.

<span class="mw-page-title-main">Kinship</span> Web of human social relationships

In anthropology, kinship is the web of social relationships that form an important part of the lives of all humans in all societies, although its exact meanings even within this discipline are often debated. Anthropologist Robin Fox says that the study of kinship is the study of what humans do with these basic facts of life – mating, gestation, parenthood, socialization, siblingship etc. Human society is unique, he argues, in that we are "working with the same raw material as exists in the animal world, but [we] can conceptualize and categorize it to serve social ends." These social ends include the socialization of children and the formation of basic economic, political and religious groups.

Endogamy is the cultural practice of mating—usually in the form of marriage—within a specific social group, religious denomination, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close interpersonal relationships. Whereas endogamy refers to marriage within the group, its opposite, exogamy, describes the social norm of marriage outside of the group.

<span class="mw-page-title-main">Consanguinity</span> Property of being from the same kinship as another person

Consanguinity is the characteristic of having a kinship with a relative who is descended from a common ancestor.

The coefficient of relationship is a measure of the degree of consanguinity between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, and was derived from his definition of the coefficient of inbreeding of 1921. The measure is most commonly used in genetics and genealogy. A coefficient of inbreeding can be calculated for an individual, and is typically one-half the coefficient of relationship between the parents.

Heterosis, hybrid vigor, or outbreeding enhancement is the improved or increased function of any biological quality in a hybrid offspring. An offspring is heterotic if its traits are enhanced as a result of mixing the genetic contributions of its parents. The heterotic offspring often has traits that are more than the simple addition of the parents' traits, and can be explained by Mendelian or non-Mendelian inheritance. Typical heterotic/hybrid traits of interest in agriculture are higher yield, quicker maturity, stability, drought tolerance etc.

<span class="mw-page-title-main">Pedigree collapse</span> Concept in genealogy

In genealogy, pedigree collapse describes how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree of their offspring to be smaller than it could otherwise be. Robert C. Gunderson coined the term; synonyms include implex and the German Ahnenschwund.

Assortative mating is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be expected under a random mating pattern. A majority of the phenotypes that are subject to assortative mating are body size, visual signals, and sexually selected traits such as crest size. The opposite of assortative is disassortative mating.

<span class="mw-page-title-main">Cousin</span> Descendant of an ancestors sibling

A cousin is a relative that is the child of a parent's sibling, this is more specifically referred to as a first cousin.

<span class="mw-page-title-main">Molecular ecology</span> Field of evolutionary biology

Molecular ecology is a field of evolutionary biology that is concerned with applying molecular population genetics, molecular phylogenetics, and more recently genomics to traditional ecological questions. It is virtually synonymous with the field of "Ecological Genetics" as pioneered by Theodosius Dobzhansky, E. B. Ford, Godfrey M. Hewitt, and others. These fields are united in their attempt to study genetic-based questions "out in the field" as opposed to the laboratory. Molecular ecology is related to the field of conservation genetics.

Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding. Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression, though inbreeding and outbreeding depression can simultaneously occur.

Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek roots philo, "liking, loving" and patra, "fatherland", although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds.

A cousin marriage is a marriage where the spouses are cousins. The practice was common in earlier times and continues to be common in some societies today, though in some jurisdictions such marriages are prohibited. Worldwide, more than 10% of marriages are between first or second cousins. Cousin marriage is an important topic in anthropology and alliance theory.

Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity.

The alliance theory, also known as the general theory of exchanges, is a structuralist method of studying kinship relations. It finds its origins in Claude Lévi-Strauss's Elementary Structures of Kinship (1949) and is in opposition to the functionalist theory of Radcliffe-Brown. Alliance theory has oriented most anthropological French works until the 1980s; its influences were felt in various fields, including psychoanalysis, philosophy and political philosophy.

<span class="mw-page-title-main">Cousin marriage in the Middle East</span>

Cousin marriage, a form of consanguinity. As of 2003, an average of 45% of married couples were related in the Arab world. While consanguinity is not unique to the Arab or Islamic world, Arab countries have had "some of the highest rates of consanguineous marriages in the world". The bint 'amm marriage, or marriage with one's father's brother's daughter is especially common, especially in tribal and traditional Muslim communities, where men and women seldom meet potential spouses outside the extended family.

Consanguine marriage is marriage between individuals who are closely related. Though it may involve incest, it implies more than the sexual nature of incest. In a clinical sense, marriage between two family members who are second cousins or closer qualifies as consanguineous marriage. This is based on the gene copies their offspring may receive. Though these unions are still prevalent in some communities, as seen across the Greater Middle East region, many other populations have seen a great decline in intra-family marriages.

Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.

References

  1. ↑ New Zealand Slavonic Journal, Victoria University of Wellington, 2002, Volumes 35-36, p.81 OCLC   297663912
  2. ↑ Helgason A, Pálsson S, Gudbjartsson DF, Kristjánsson T, Stefánsson K (February 2008). "An association between the kinship and fertility of human couples". Science. 319 (5864): 813–6. Bibcode:2008Sci...319..813H. doi:10.1126/science.1150232. PMID   18258915. S2CID   17831162.
  3. ↑ Labouriau R, Amorim A (December 2008). "Comment on "An association between the kinship and fertility of human couples"". Science. 322 (5908): 1634, author reply 1634. Bibcode:2008Sci...322.1634L. doi: 10.1126/science.1161907 . PMID   19074330.
  4. ↑ Verhoeven KJ, Macel M, Wolfe LM, Biere A (January 2011). "Population admixture, biological invasions and the balance between local adaptation and inbreeding depression". Proceedings. Biological Sciences. 278 (1702): 2–8. doi:10.1098/rspb.2010.1272. PMC   2992731 . PMID   20685700.
  5. ↑ Thornhill N (1993). The Natural History of Inbreeding and Outbreeding: Theoretical and Empirical Perspectives. Chicago: The University of Chicago Press.
  6. ↑ Dorsten LE, Hotchkiss L, King TM (May 1999). "The effect of inbreeding on early childhood mortality: twelve generations of an Amish settlement". Demography. 36 (2): 263–71. doi: 10.2307/2648113 . JSTOR   2648113. PMID   10332616. S2CID   26311145.
  7. ↑ Tchen P, Bois E, Feingold J, Feingold N, Kaplan J (September 1977). "Inbreeding in recessive diseases". Human Genetics. 38 (2): 163–7. doi:10.1007/BF00527398. PMID   302820. S2CID   8849012.
  8. ↑ McLennan JF (1888). "The Origin of Exogamy". The English Historical Review. 3 (9): 94–104. doi:10.1093/ehr/iii.ix.94.
  9. ↑ Fraser JG (1910). Totemism and Exogamy Vol. IV. New York: Cosimo Inc. pp. 100–102. ISBN   9781605209814.
  10. ↑ Morgan LH (1871). "Systems of Consanguinity and Affinity of the Human Family". Smithsonian Contributions to Knowledge. Smithsonian Institution. 41 (2).
  11. ↑ Frazer JG (1910). Totemism and Exogamy Vol. IV. New York: Cosimo Inc. p. 95. ISBN   9781605209791.
  12. ↑ "Alliance Theory". Encyclopædia Britannica. Retrieved 15 March 2012.
  13. ↑ Bose JK (1980). Glimpses of Tribal Life in North-east India. Calcutta. p. 52.{{cite book}}: CS1 maint: location missing publisher (link)
  14. ↑ Turkish Studies Association Bulletin, 1982, Volume 6, p.79
  15. ↑ Potapov LP (1969). "Ethnic Composition and Origin of Altaians". Science. Leningrad: 44.
  16. ↑ Effects of the growth of human activities on the Taï forest of the south-west of the Ivory coast (PDF). UNESCO. December 2017.[ permanent dead link ]
  17. ↑ Fainberg L (1967). "On the Question of the Eskimo kinship system". Arctic Anthropology. 4 (1): 244.
  18. ↑ Golovnev AV. "From One to Seven: Numerical Symbolism in Khanty Culture". Arctic Anthropology. 31 (1): 62–71.
  19. ↑ Jackson JE (1983). The Fish People - Linguistic Exogamy and Tukanoan Identity in Northwest Amazonia. Cambridge University Press.
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