Cousins & Cousinhood

It's All Strictly Relative

Disclaimer: The information on this page was extracted from Frank Arduini's site at before the site disappeared. I did not do the work and am not taking credit for it, but believe it is an excellent resource. Ted Cash

It takes very little time before the average genealogical researcher is confronted with the issue of cousins and cousinhood. And for those of us who think we've got it figured out (and therefore dare to use it in conversation) one of the most common phrases we hear is, "What the hell does that 'once removed' stuff really mean, anyway?"

This is my feeble attempt at explaining the issues around cousinhood, how it is measured, and what it means. I believe I've actually got a pretty good handle on the subject, but if I'm wrong please let me know as soon as possible.

Here is a chart I've drawn which illustrates (I hope) the key points. Take a look at the chart, and then let's discuss what it means and how to read it.

How to Basically Read the Chart:

To begin, pay attention to the red rectangle, because that represents you. All the other rectangles represent a blood relative of yours, and within each rectangle the nature of that blood relationship is described.

The first number is your traditional degree of kinship with the person in that block. This is the way we legally define how closely related we are, and it is the degree of kinship recognized by both the civil and religious authorities who are likely to care about such things. It is calculated by counting the number of steps it takes to move on the chart from that person to you. It's one step from you to your parent, so you are kin of the 1st degree. Very simple.

Now, this way of measuring kinship was developed long before anybody had ever heard of Mendelian genetics, so it's actually wrong in a couple of areas, but not enough to really matter to most of us. For working purposes, lets just say that the smaller the number, the more closely related you are.

Next, the block actually names the relationship between that person and you. We'll go into more detail on that in just a moment.

The last number (shown as a percentage) shows the actual genetic degree of relationship, and the number represents the total percentage of your genes that you share with that relative. So, for each of your parents you will share 50% of their genes. Same with your siblings.

Notice that this is different from your traditional degree of kinship. According to the traditional measure you are 1st degree kin to your parents and children, but only 2d degree kin to your siblings. But in actuality, you are equally related to all of them, sharing 50% of your genes with each.

Direct and Collateral Relationships:

We are related to our other family members in one of three ways: We are either direct relatives, collateral relatives, or both.

Direct relatives measure lines of direct descent. Anyone in that line will either be a direct ancestor, or a direct descendant of you, and in the chart I've colored all those folks in green.

Collateral relatives are all others to include siblings, aunts & uncles, nieces & nephews, and all cousins. Collateral relatives share a common ancestor, but are not directly descended from or ancestral to each other.

Now these categories are not mutually exclusive. For example, my great-grandparents were 2d cousins once removed from each other. That means that all their descendants are related to each other more than one way. Some of those relationships are direct, and some are not. I am (for example) my mother's son, her 4th cousin, her 5th cousin, and her 4th cousin once removed.

Okay! What the heck are these "removes" about?:

If you look at the chart again, you'll notice that I've colored one row blue. This row represents all the people on the chart who are members of your generation. Move up one row, and you're looking at your parent's generation. Down one row and you're looking at your children's.

Full siblings and cousins are all members of the same generation! In other words, they've descended the same number of steps from the shared ancestors. Siblings share a set of parents. 1st cousins share a set of grandparents. 2d cousins share a set of great grandparents. And on it goes...

So if you and your 1st cousin share a set of grandparents, then how are you related to your 1st Cousin's children?

They are not in the same generation as you. They are one generation further away from those common ancestors (your grandparents, their great grandparents). They are (Taaa daaaa!!!) one generation removed from your generation.

Now your 1st Cousin's children and your children are in the same generation again, but the shared ancestors are their great grandparents. That means that they are full 2d cousins. And your 1st cousin's grandchildren will be 3d cousins to your grandchildren, 2d cousins once removed to your children, and 1st cousins twice removed from you.

Whoa!!! Hold on here! How come the "cousin number" keeps changing along with the "removed number?" The rule here is that as you count the generations from the shared ancestors along each branch, the shortest branch controls the "cousin number." If the shortest branch only has two generations between the ancestors and the relative in question, then that's the baseline, 1st cousins. So, all the generations "removed" are measured from there.

Another way of thinking of it is to move down each generation until you get to the last generation where both branches are the same length. If that is the 1st cousin generation, then all the remaining links along the longer branch will be 1st cousins, as many times removed as they are farther along the branch.

Great Uncles and Grand Aunts:

One of the most common mistakes we all make (I still make it constantly) has to do with the official name for the relationship between us and the siblings of our grandparents. Most of us tend to call them great aunts & uncles. Well, when we do that we are all WRONG!!!

Officially, those are our grand (not great) aunts and uncles. And the siblings of our great-grandparents are our great-grandaunts & great-granduncles. It's actually very neat and tidy, making much more sense than the wrong way we all insist on using.

I don't expect most of us will find it easy to change this habit, I know I certainly haven't. But I figured as long as I was on the subject.

A Little Bit About Halves and Doubles:

As one final interesting aside, how are we related to our half siblings, half 1st cousins, all that stuff. Well, it's pretty simple and just like it sounds. We're half as related to our half relatives as to our full relatives.

So, we share 50% of our genes with our siblings? Then we share 25% of our genes with our half siblings. We share 12.5% of our genes with our 1st cousins? Then we share 6.25% of our genes with our half 1st cousins.

But where this gets really fun is with doubles. Many of us have these. My grandfather (Francesco Pizzo) had a little brother Salvatore. And my grandmother (Maria la Furia) had a little sister Michela. Francesco and Maria married and had my Uncle Angelo Pizzo. Salvatore and Michela also later married and had a son, Angelo Pizzo. How are the two Angelos related?

They are double 1st cousins, since they share both sets of grandparents, paternal and maternal. This also means that they share twice as many genes as ordinary 1st cousins, fully 25%. They are as closely related as if they had been uncle and nephew.

Of course, this also means that their children are double 2d cousins, and their grandchildren are double 3d cousins. And on and on and on....

A final special case is, of course, identical twins. From the genetic perspective, identical twins are really the same person. They share 100% of their genes. Now the children of an identical male twin are as closely related to their uncle as they are to their Father. And 1st cousins descended through a pair of identical twins are double 1st cousins, just as if their grandparents had been two pair of siblings.

The extra fun comes in when two sets of identical twins marry. When that happens, the 1st cousins are actually quadruple 1st cousins. This makes them (genetically at least) siblings.

Whew! Now I know why lawyers and churches stick with the traditional degree of kinship over the genetic one.

So what practical use is any of this?

I don't know, probably not much until you start fighting over inheritances, and I don't intend to get involved in that. Hopefully though, we can now all begin to feel a little more superior in knowing that when we refer to our 3d cousin 6 times removed, at least we can make the case that what we've said is true, in some cosmic way.