Endogamy

Endogamy is the practice of marrying within a specific social group, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close personal relationships.
Endogamy is common in many cultures and ethnic groups. Several religious and ethnic religious groups are traditionally more endogamous, although sometimes with the added dimension of requiring marital religious conversion. This permits an exogamous marriage, as the convert, by accepting the partner's religion, becomes accepted within the endogamous rules. Endogamy, as distinct from consanguinity, may result in transmission of genetic disorders, the so-called founder effect, within the relatively closed community.
Adherence.
Endogamy can serve as a form of self-segregation; a community can use it to resist integrating and completely merging with surrounding populations. Minorities can use it to stay ethnically homogeneous over a long time as distinct communities within societies that have other practices and beliefs.
The isolationist practices of endogamy may lead to a group's extinction, as genetic diseases may develop that can affect an increasing percentage of the population. However, this disease effect would tend to be small unless there is a high degree of close inbreeding, or if the endogamous population becomes very small in size.
Social dynamics.
The Urapmin, a small tribe in Papua New Guinea, practice strict endogamy. The Urapmin also have a system of kinship classes known as "tanum miit". Since the classes are inherited cognatically, most Urapmin belong to all of the major classes, creating great fluidity and doing little to differentiate individuals.
The small community on the South Atlantic island of Tristan da Cunha are, because of their geographical isolation, an almost endogamic society. There are instances of health problems attributed to endogamy on the island, including glaucoma and asthma as research by the University of Toronto has demonstrated.
Examples.
Other examples of ethnic and religious groups that practice endogamy include:
See also.
Cousin marriage:
Marriage systems: