Civil Degree.

The civil degree system was devised by the Romans and used as a formal basis for establishing customary and legal regulations on such matters as property inheritance or incest prohibitions. The Roman/civil system was continued in some European settings after the fall of the Empire and is still used in some contemporary Western legal and social systems. The Catholic Church changed its kinship degree calculation from the canon to the civil system as part of the Vatican II reforms.

In the civil system, kinship degrees are simply calculated by adding the number of links from one of the relatives in question, Ego, to the common ancestor, and those that connect the ancestor to the other relative, Alter.

Figure 24: Counting Kin
According to the Civil Degree System

Civil degree is calculated by counting the links from Ego to a nearest common ancestor and then continuing to count down the generations to Alter.
In this case

Ego is 4 generations removed,
Alter is 3 generations removed, and

the degree of their relationship is 7, the sum of the two components

The following pattern of assigning degree results.

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The civil system has an important advantage insofar as it is equivalent to a genetic measure, the inbreeding coefficient, which predicts the probabilities that each of two intermarring relatives will pass on the an allele (variant form of a gene) inherited from a common ancestor to one of their children, making him/her homozygous for the trait.