FIGURING OUT RELATIONSHIPS

The two co-managers of this web page are sixth cousins once removed. What in the world does that mean? And why do we need to define relationships like this anyway? Who invented these definitions?

The two most widely used systems for defining "degrees of consanguinity" between individuals are the Canon and the Civil systems. They commonly differ in the number they generate for a given pair of cousins. What is a "degree of consanguinity"?

I know and you know, you can do a search on the Internet and read all sorts of authoritative tomes on these subjects. Maybe you should – it will be interesting. But since most people are in a hurry nowadays, I am writing this simplified overview. Keep in mind, it IS simplified!

The "degree of consanguinity" is the measure of how closely two people are considered to be related by blood (i.e. genetically.) The catch is that "are considered to be" part, because it depends on who is doing the considering. There is in fact a very scientific way to look at the closeness of the blood relationship, and that is to determine what percentage of their genes came from their nearest common ancestor. No one seems to have developed a system on that basis yet. (If you do so, please post it here!)

The earliest systems for determining degree of consanguinity were religious in origin, and applied to who could and who could not be married to each other. As usual with early religions, the rules (Canons) are expressed clearly and the reasoning behind the rules are barely expressed at all. They are all implementing God's will, which has always made me wonder why God had a different will for different religions in these matters. Eventually civil government got into the picture, and the Roman system became what we tend to call the Civil system today.

Even closely related religions can differ in their rules about what degree of consanguinity forbids marriage, because there are two conflicting descriptions of the origin of Adam and Eve in the Book of Genesis. According to one, they were made separately out of the elements of the Earth, so relate to each other only as "non-sanguinous" mates. In the other, Eve was cloned from Adam's rib, presumably involving throwing out the Y-chromosome and replacing it with a second copy of the X-chromosome so she would be female. In this case she was his twin sister. The Roman Catholic Church, for example, considers them brother and sister.

We must first define "common ancestor". Two people have a "common ancestor" when the same individual, male or female, appears relative to them as a parent, grandparent, great grandparent, etc. in both of their family trees. That individual does not have to have the same named relationship in both cases; it could be a great grandmother of one and a great, great grandmother of the other for example. Surnames are irrelevant in this - it does not matter how many times one has to branch from a male line to a female line to get there. Whether or not a given pair of parents were legitimately married or not is also irrelevant. We are concerned with the passing on of genetic information (DNA), not inheritance rights.

The Civil system is fairly easy to describe. For a given two people whose degree of consanguinity is to be determined, one starts back from one of them. One counts the steps backward, for example to father, grandfather, great grandfather, and so on, until one comes to their first common ancestor. Let's say it took four steps. Then count back from the other one until you get to the same ancestor; suppose it takes three steps. Add the two numbers together (I get seven), and you get the Civil degree of consanguinity. Then civil law (different in different countries) will specify that the number must be greater than (whatever) in order for those two to marry.

The Canon system changed many times through history, but at present in the Roman Catholic version one only counts the number of steps from one of the two back to that common ancestor, whichever of the two takes more steps. In the case above, the degree of consanguinity would be "of the fourth degree."

What about when you have to branch into a line that connects by marriage? Suppose to get to a common ancestor you have to go back father to grandfather to great grandfather to great, great grandmother to her father, to her father's mother. The surname changed twice. That makes no difference. Just count those steps (I get six.)

So much for the easy part. Suppose you don't have a common direct ancestor, but you can step sideways to your grandfather's brother's wife and follow back from there to a person in the other direct line? There is no blood relationship, no degree of consanguinity. This is called an "affinal" relationship, and at least in the United States is not an impediment to marriage no matter the number of steps involved.

In the Uniat Eastern Churches second cousins can not marry without special dispensation and third cousins are to be discouraged from marrying (seven degrees of consanguinity – Civil System.) The Roman Catholic Church forbids marriage of third cousins (four degrees of consanguinity – Canon System.) Russian Orthodox churches forbid marriage of first cousins, and the National Greek Church of second cousins. All the religious proscriptions can be set aside if a petition for a special dispensation is granted.

How about descendants of half-siblings (same mother, different fathers; or same father, different mothers)? In general the religious systems treat half-siblings as equivalent to full siblings in the calculations. Here is one area in which the Civil system may differ from country to country, and you will probably need a lawyer to figure out what the rules are.

Cousins? The closest blood relationships have been given specific names, like father, mother, son, daughter, sister, brother, uncle, aunt, nephew, niece. To go on from there in a direct line we add "grand" and then an endless series of "great". But that's as far as anyone wanted to go in inventing unique names. Any two people who share a common ancestor but do not have one of the specifically named relationships above, are cousins of one sort or another. To distinguish between cousins of different degrees of consanguinity we add simple prefixes like 2^nd, 3rd and so on. The calculation is similar to that for the Canon above, with two changes. Count the steps back to the common ancestor for the individual who has the smaller number of steps involved, and subtract 1. That is because if your father is the common ancestor you are siblings instead of cousins, so that step doesn't count. The number you wind up with matches the 2nd, 3rd or whatever cousins they are.

For example if the shorter route back to the common ancestor is father to grandfather to great grandfather to great, great grandfather, that makes them third cousins (four steps, minus 1.) Now do the same thing for the other person. Suppose this time it takes six steps. Subtract the smaller number of steps from the larger number of steps. I get two. Then they are "third cousins twice removed" where "removed" means they are not considered members of the same generation relative to that common ancestor. They are two generations removed from each other. If one line leads to the common ancestor through one of his children and the other through a half-brother of that child, the original two people would be "half-third cousins twice removed."

So to answer the first question in this article, Gloria Albro Silverman and I are sixth cousins once removed because our closest common ancestor is my great, great, great, great, great grandparent (or, to use another genealogical convention, my 5th great grandparent, seven steps), and her 6th great grandparent (one more great than mine, one step removed.) That makes us the XVth degree of consanguinity in the Civil System, 8th degree in the Canon System. I'm sure this is now perfectly clear.

Recommendations for further reading:

The Catholic Encyclopedia – Consanguinity (available on-line at http://newadvent.org/cathen/04264a.htm)

The Columbia Encyclopedia, Sixth Edition, 2001, consanguinity (available on-line at http://www.bartleby.com/65/co/consangu.html)

For an excellent chart that makes calculating cousin relationships easy see:
http://www.cswnet.com/~sbooks/genealogy/cousins/cousins.htm

Phil Albro, 09/29/2001