Consanguinity, literally meaning common blood, describes a family relationship between two individuals. A consanguinity chart (or table), as seen below, is often used to illustrate that relationship.

Consanguinity is measured in terms of the degree of consanguinity, which can be defined in several different ways. In general, the lower the degree of consanguinity, the closer the relationship, and thus the higher the level of consanguinity. The most common definition is the modern civil law definition, which increases by one with each step up or down along the shortest path between two individuals in a family tree; thus, for example, you are one degree from either parent, or from your children; two sibilings are two degrees apart -- one step up to the common parent, another back down to the sibling. This is also the definition used in Roman law.

Various other definitions of degrees of consanguinity have been used at different times in canon law.

In general, the lower the number of degrees of consanguinity, the higher the risk of inbreeding. Most cultures regard sexual relationships between people with high levels of consanguinity as incest, and forbid marriages between such people.

In the Catholic Church, a marriage with a direct line relative or collateral relative to the fourth degree is grounds for an annulment. In other words, you could not marry your 1st cousin (4th degree), grand nephew/niece (4th degree), but you could marry your 1st cousin once removed (5th degree).

Given that most of the nobility of Europe were and still are in-bred to one degree or another, consanguinuity was often used by European nobility as a convenient means of divorce, especially in ages when religious doctrine forbade the voluntary dissolution of a failed marriage.

The succession law known as consanguinity, requires that the next monarch be of the same blood of the previous monarch; allowing, for example, illegitimate children to inherit.

To be covered:

• Lineal consanguinity
• Collateral consanguinity
• Coefficient of consanguinity

See also

• Bloodline
• Blood relative
• Inbreeding
• Mendelian inheritance
• Outbreeding
• Pedigree collapse

External links

• Consanguinity chart showing different schemes for calculating degree of consangunity
• Catholic Encyclopedia article on consangunity
• Mathematics of the coefficient of consanguinity
• Genetic consanguinity