Consanguinity is the degree of relationship of family members who share at least one common ancestor. It is the blood-relationship (cognatio naturalis), or the natural bond between persons descended from the same stock. When persons are related by a direct line of descendancy from a common ancestor, it is called lineal consanguinity. When persons are related by descendancy from a common ancestor, but not in a direct line, it is called collateral consanguinity.
Degrees of consanguinity sometimes are controlling in rights of inheritancy. In the United States all the states prohibit marriage between lineal descendants; most of them prohibit marriages between uncle and niece, nephew and aunt, and between first cousins.
