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.
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.
If a cousin marriage has accrued in a known ancestral tree of a person, in historical time, it is referred to as pedigree collapse. This may cause relations along multiple paths between a persons autosomal-DNA matches. It creates stronger DNA matches between the DNA matches than expected from the nearest path.
Cousin marriage should not be confused with double cousins, which do not cause a pedigree collapse. Certain levels of sibling marriage and cousin marriage is prevented by law in some countries, and referred to as consanguinity.
A long term pattern of endogamy in a region may increase the risk of repeated cousin marriage during a long period of time, referred to as inbreeding. It may cause additional noise in the DNA autosomal data, giving the impressions that DNA matches with roots in that region are more closely related than they are.
Judaism traditionally mandates religious endogamy, requiring that both marriage partners be Jewish, while allowing for marriage to converts. Orthodox Judaism maintains the traditional requirement for endogamy in Judaism as a binding, inherent part of Judaism's religious beliefs and traditions.
The Knanaya, an endogamous group within the St. Thomas Christian Community of India. The community claims to have arrived to India in the fourth century and have been noted for their historical practice of endogamy.