Bifurcate merging

Iroquois kinship (also known as bifurcate merging) is a kinship system. Identified by Lewis Henry Morgan in his 1871 work Systems of Consanguinity and Affinity of the Human Family, the Iroquois system is one of the six major kinship systems (Eskimo, Hawaiian, Iroquois, Crow, Omaha, and Sudanese).

The system has both classificatory and descriptive terms. In addition to gender and generation, Iroquois kinship also distinguishes 'same-sex' and 'cross-sex' parental siblings: the brothers of Ego's (the subject from whose perspective the kinship is based) father, and the sisters of Ego's mother, are referred to by the same parental kinship terms used for Ego's Father and Mother. The sisters of Ego's father, and the brothers of Ego's mother, on the other hand, are referred to by non-parental kinship terms, commonly translated into English as "Aunt" and "Uncle".

The children of one's parents' same-sex siblings, i.e. parallel cousins, are referred to by sibling kinship terms. The children of Aunts or Uncles, i.e. cross cousins, are not considered siblings, and are referred to by kinship terms commonly translated into English as "cousin". In some systems, the kinship terms applied to cross-cousins are the same as those applied to brothers-in-law and sisters-in-law, due to preferential marriage practices (see below).

Ego (the subject from whose perspective the kinship is based) is encouraged to marry his cross cousins but discouraged or prohibited from marrying his parallel cousins. In many societies with Iroquois kinship terminologies, the preferred marriage partners include not only first cousins (mother's brother's children and father's sister's children), but more remote relatives who are also classified as cross cousins by the logic of the kinship system. Preferential cross-cousin marriage can be useful in reaffirming alliances between unilineal lineages or clans.

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