Systems of Consanguinity and Affinity of the Human Family

Systems of Consanguinity and Affinity of the Human Family is an 1871 book written by Lewis Henry Morgan (1818 - 1881) and published by the Smithsonian Institution. It is considered foundational for the discipline of anthropology and particularly for the study of human kinship. It was the culmination of decades of research into the variety of kinship terminologies in the world conducted partly through fieldwork and partly through a global survey of kinship terminologies in the languages and cultures of the world.

It "created at a stroke what without exaggeration might be called the seminal concern of contemporary anthropology, the study of kinship..." In the book Morgan argues that all human societies share a basic set of principles for social organization along kinship lines, based on the principles of consanguinity (kinship by blood) and affinity (kinship by marriage). At the same time, he presented a sophisticated schema of social evolution based upon the relationship terms, the categories of kinship, used by peoples around the world. Through his analysis of kinship terms, Morgan discerned that the structure of the family and social institutions develop and change according to a specific sequence.

Morgan's interest in kinship systems came from his interest in the history and society of the Iroquois league, particularly the Seneca which he knew well. Studying Iroquois social organization, he discovered their matrilineal system of kinship reckoning, and this was what spurred his interests in kinship terminology. The Iroquoian kinship system used the same kin terms for all male blood relatives on the father's side (i.e., a father's brother is mentioned with the same term as father), and all female blood relatives on the mother's side (i.e., mother's sisters are mentioned with the same term as mother). This is a system later called "bifurcate merging" or Iroquoian kinship following Morgan. Having discovered that the typical European way of organizing kin relations was not universal, Morgan came to suspect that other languages in the Americas and perhaps in Asia had similar systems and began an investigation.

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