What is Consanguinity?

Consanguinity is the property of having the same kinship as another, or, in other words, having an ancestor in common. There are degrees of consanguinity; for example, sisters are more closely related than cousins, as the former have a common ancestor only one generation away. There may also be different definitions of consanguinity, as is often the case for legal purposes. For example, if a law stipulates that relatives may not marry each other, the definition of relative may be limited to those sharing a parent or grandparent, but not to those with only a great-grandparent in common.

The kinship relations of a group of individuals may be depicted in a consanguinity tree, commonly called a family tree. In a family tree, each generation is usually shown on a separate line or column, with solid lines indicating descent and dashed lines indication marriage. Consanguinity is sometimes taken to include adoptive relationships in addition to genetic ones. Some cultures consider two people to have the same kinship if they share a male ancestor, but not a female ancestor, or vice versa. Kinship relations are sometimes distinguished between consanguinity, or genetic decsent, and affinity, or marriage-based relationships.

In addition to anti-incest marriage laws, consanguinity may be used to determine who inherits the estate of a person who dies without leaving a will. For example, the person with the least generations of ancestral separation from the deceased may be the default inheritor. In the United States, if the deceased has a living spouse, he or she inherits the estate, while any children are next in line. If the deceased has no descendants, the parents of the deceased stand to inherit. If there are no living children or parents, the descendants of the deceased's parents -- i.e. the siblings of the deceased -- inherit the estate, followed by the descendants of the deceased's grandparents.

Genetic consanguinity can also be used to determine a person's risk of inheriting certain genetic disorders. If one's parents both had a genetic condition, or if two or more grandparents had it, there is often a greater risk that person will develop the disorder. Married couples are often tested for the presence of genes responsible for certain disorders to consider the risk that their children will have it.