Consanguinity or how do you determine which relationship is closest?

+5 votes

Long before we had DNA testing and a scientific understanding of genetics, there were secular and religious laws based on one person's degree of consanguinity with another. Laws governing marriage, inheritance and other areas looked at a person's degree of consanguinity which may also be thought of as one's degree of kinship or blood relatedness.

The simple cases are easy. We know intuitively that we are more closely related to a sibling that we are to a first cousin but the "closeness" of our kinship can quickly become more difficult to discern. Am I closer to my second cousin or to my first cousin, once removed? Now throw in generational differences and half relationships and it becomes very problematic.

What I am looking for is an analytical approach to determining the “degree of consanguinity” between myself and any other individual in my family tree.

Consanguinity is derived from the Latin and refers to the property of being from the same bloodline as another person. You share bloodline relationships with anyone who descends from a common ancestor. The degree of consanguinity is a measure of this shared bloodline and it should correlate closely to the amount of genetic material you share with someone related to you.

These consanguineous relationships can be lineal, which are straight forward and deal only with straight line direct relationships like you, your parents, grandparents, great-grandparents, children, grandchildren, etc. or collateral which can become quite complex. Additionally there is a third type that takes into account half relationships.

I would like to be able to quantify multiple bloodline connections to an individual to determine the degree of consanguinity. I assume the multiple comnnections are additive but probably not always in the same proportion. I would also like the ability to take half aunts, uncles and cousins into account and to factor in whether a cousin who is “removed” is younger than I and hence farther away from our common ancestor or older than I and therefore closer to our common ancestor. I'm not sure if this makes difference or not.

There are several charts available that that illustrate the consanguinity problem simplistically but I was unable to find anything in the literature that would help me calculate what I was after. So I was really just curious to see if anyone had knowledge of a program or system that would let one quickly determine a numeric value for consanguinity for purposes of comparison.

Yeah, I know, I have way too much time on my hands. {GRIN}

Here are a few general examples of the types of relationships I have been puzzling over:

  • Would I be more closely related, i.e., have a higher degree of consanguinity with my 1st cousin thrice removed or my 2nd cousin, once removed? Now what if one or the other was younger than I rather than older?
  • Say Bill is my 3rd cousin, twice removed two different ways through one line and my 4th cousin, once removed through another line. Another ancestor, Bob, is my half 2nd cousin, twice removed and my 3rd cousin, three times removed. Given those relationships, am I more closely related to Bill or to Bob?
  • If my grandparents were descended from a common ancestor, I'll call Ezekiel, do I have a "double dose" of Ezikiel's genes, i.e., am I more closely related to Ezekiel than I am to my other grandparents of that same generation or are the genes from him not replicated in some manner? What if there were a different spouse for Ezekial for one of my granparents?

It’s not rocket science but neither is it intuitively obvious. I was hoping that someone had already developed a quick and easy little program that would have enough flexibility to let me do some similar and some more complicated degree of consanguinity calculations.

The degree of consanguinity has had both civil and religious ramifications over the millennia. There are statutes in every state that use consanguinity to resolve matters involving inheritance, marriage, custody, employment rights, etc. Additionally Canon Law has long used some degree of consanguinity calculation to determine who may and who may not marry within the church.

Churches of different faiths and denominations have used different measures and methods for determining who may or may not marry within their church and these ecclesiastical laws are by no mean consistent or unchanging.

 DNA testing could theoretically help answer all my questions but that isn't really feasible. Just for your information, at present only about 8% of the US population, or 26 million people out of 329 million, have availed themselves of the home testing kits designed for genealogical purposes.

Please post here or contact me if you know of a computer program that does what I am seeking. My email address is and yes I am fully aware of possible negative consequences associated with posting one's email address on a public site and I assume full responsibility. Thanks in advance to anyone else who might take an interest in this genealogical puzzle.


in The Tree House by Anonymous Magyar G2G6 Mach 1 (19.2k points)
There are charts that show what the theoretical % of shared DNA is for all sorts of relationships to see where they fit.  You don’t need the DNA to know that the percents are  50% for parents and siblings,  25% grandparents, aunts, uncles, double first cousins, 12.5% for first cousins, great-grandparents or grandaunts, etc. , but all those numbers (except for parents or an identical twin) are just an average or expected amount and can vary from all to nothing.  Just google shared autosomal relationship chart and you’ll get charts and articles.

Hi Kathie,

I am a big proponent of DNA testing and I've taken the Y-DNA, the mitochondrial and the autosomal tests offered by Family Tree DNA and also the test.

These tests have allowed me to find many matches with others who have taken the same tests or perhaps uploaded results from a different lab to GEDmatch.

The answers I'm seeking above deal with the relative amount of  "blood relatedness" of ancestors and cousins, many deceased long ago, not the amount of shared genetic material. The cemeteries tend to get a little upset when you try to dig up your 4th cousin, twice removed for a DNA sample. <grin>


1 Answer

+4 votes
This may help to the find the answer to some of your questions  -  - as it gives a relatedness coefficient and a degree of relation which you can compare.
by Samantha Thomson G2G6 Mach 7 (71.3k points)

Hi Samantha,

I communicated with Nolan Lawson shortly after he released his Relatedness Calculator on the web back in 2012. He pointed out that his app did not account for "X times removed" when trying to calculate the consanguinity for a distant cousin. He did offer some work arounds that were too cumbersome for what I am trying to do. There may have been a problem with half and double relationships as well. It is still the closest tool I am aware of that looks at these types of genealogical relationships.


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