Consanguinity

Consanguinity is the quality of being descended from the same ancestor as another person.

The degree of relative consanguinity can be illustrated with a consanguinity table, in which each level of lineal consanguinity (i.e., generation) appears as a row, and individuals with a collaterally-consanguinious relationship share the same row.

The connotations of degree of consanguinity varies by context (e.g., Canon law, Roman law, et al.). Most cultures define a degree of consanguinity below which sexual interrelationships are regarded as incestuous. In the Catholic Church, unwittingly marrying a closely-consanguinious blood relative is grounds for an annulment. Adoption may or may not be considered at law to create such a bond; in most Western societies, adoptive relationships are considered blood relationships for these purposes, but in others, including both Japan and ancient Rome, it was common for a couple with only daughters to adopt a son-in-law, making the marriage one between adoptive siblings.

Historically, some European nobles cited a close degree of consanguinuity when they required convenient grounds for divorce, especially in contexts where religious doctrine forbade the voluntary dissolution of a failed marriage. Conversely, the consanguinity law of succession requires the next monarch to be of the same blood of the previous one; allowing, for example, illegitimate children to inherit.

The word consanguinity is used in the United States Declaration of Independence.

"We have reminded them of the circumstances of our emigration and settlement here. We have appealed to their native justice and magnimity, and we have conjured them by the ties of our common kindred to disavow these usurpations, which, would inevitably interrupt our connections and correspondence. They too have been deaf to the voice of justice, and of consanguinity. We must, therefor, acquiesce in the necessity, which denounces our separation, and hold them, as we hold the rest of mankind, Enemies in War, in Peace Friends."