What is a 4th Cousin?

Are those 4th cousin matches actually blood-related?
Marc McDermott

If you’ve taken a consumer DNA test and got a long list of 4th cousin matches, you might be a bit confused. So, what is a 4th cousin and how are they related to you?

When someone has a 4th cousin they share a complete set of Great-Great-Great Grandparents (3rd Great Grandparents).

One of the most confusing aspects of DNA databases such as 23andMe and AncestryDNA are their assumptions of how you relate to a DNA match. While, most of the time, they are not too far off, the data can be skewed. We are going to discuss how to determine whether or not the algorithms that pinpoint your relation to a “4th Cousin” are truly accurate and, if not, how can you go about proving or disproving that relationship? Are you actually blood-related to that 4th cousin match?

When looking at a DNA match who is put under the guise as a “4th – 6th cousin” it is vital to look specifically at the exact amount of DNA you share with that person. The measurement of DNA you share with cousins will be listed in AncestryDNA in cM’s (centimorgans) and on 23andMe as percentages (also cM’s). See what is a centimorgan.

What is a 4th Cousin – 6th Cousin?

When scrolling through DNA matches who are “4th – 6th cousins” it is important that you look into each match independently. Doing so, you will notice that the algorithm which denotes “4th – 6th cousins” does not take half cousins and cousins removed into account. By looking individually at these cousins you are able to depict your most likely relation. There are a plethora of online tools that, using the cM’s or percentages, will tell you the likelihood of your relationship with that cousin.

One of my favorite tools is the Shared cM tool from DNAPainter.com. This tool allows you to input the amount of cM’s (or percentage) and it calculates the most likely scenarios of how you relate to a DNA match. To the consumer, It is a general assumption that a 4th – 6th cousin is indeed a 4th – 6th cousin but, let’s look at the example below. I also created a similar tool that shows how predicted relationships can overlap based on the total shared DNA.

The DNA of 4th cousin matches

Johnny shares 62 cM with a DNA match named Alice who his consumer website lists as a “4th – 6th cousin”. Johnny turns to the shared cM tool to determine how it is they likely relate to one another.  The shared cM tool populates the following:

Johnny, from this tool, is visually able to determine that he is most likely (31%) related to Alice is a 2nd Cousin twice or three times removed or a Half 3rd Cousin or 3rd cousin once removed. Using this data they are able to determine that Alice and Johnny share a set of great great grandparents. Their generations are quite different and, with some family research, they are able to determine they are 2nd cousins 3 times removed. Not a 4th – 6th Cousin. Johnny learned to approach each DNA match independently in order to pinpoint their relationship.

So, why would Johnny’s DNA website display his 2nd cousins 3 times removed as a 4th – 6 th cousin? With such vast data, these company’s algorithms are not able to display the likelihood scenario of DNA matches individually, thus they display them in such vast groupings.

The websites cannot possibly display each DNA match like the above shared cM chart without overwhelming the consumer thus, they display them under 4th – 6th cousins. This also makes the website user friendly and visually pleasing. It would also be very difficult to put each DNA match through an algorithm like DNAPainters Shared cM tool all the while keeping the website from being overtaxed and incredibly difficult to navigate.

The short of it is, the data from DNA matches are already overwhelming. When someone sees the world centimorgan they run for the hills. It is a natural first reaction and, afterall, we are consumers not scientists.

Some 4th – 6th Cousins are truly 4th – 6th Cousins

The lower the cM’s you share with your matches, the likely they are actually 4th – 6th cousins. However, it is still important to approach these cousins individually the way Johnny did with Alice in our example.

What can be done with “4th Cousins”?

“4th cousin” matches, which could be 2nd or 3rd cousins with generational removals, open up a wide range of research opportunities. If they are a half 2nd cousin  X times removed then you know that the shared matches you share with said “4th cousin” come from that one great great grandparent. This is incredibly helpful for grouping and organizing your DNA.

By utilizing and adding these cousins into your family tree, you are using the ultimate source to confirm your ancestry. These DNA connections, whether near or far, are the only once source that cannot be wrong. When it comes to census records, our ancestors could have lied about their age, race, even name all the while, on top of that, the census taker would usually spell it phonetically. The paper trail is only as reliable as long as those records match up and survive the trials of time – fires, wars, floods, etc.

If you are using your DNA matches as an adoptee, it is important to keep hope alive and to understand that 4th – 6th cousins can very well be much closer.  When someone in search of their biological roots doesn’t have any 1st – 2nd cousin matches populated, it often seems that the search is hopeless. However, this is not the case.

Not too Distant After All

4th cousins, though they may seem distant, are not that distant in the scheme of things. I always encourage people to reach out to their DNA matches and ask if they would like to collaborate on family research. Most of the time, if they have taken a consumer DNA test kit and especially if they have a family tree, they will kindly oblige. In making these connections, genealogists are broadening their scope and through this type of team work so much information can come to light. The sharing of family photos, stories, and heirlooms are something that most genealogists have had in forming close relationships with distant cousins, it is just another sense of belonging that genealogy gives us.

Many families have a tale that gets passed down and, most of the time, this tale is immersed in mystery. In making connections with distant cousin matches, a certain family tale brought distant cousins together and solved some answers.

Nathan Rothstein came from Ekatarinoslov, Russia and lived in Alberta where he married and had a son. Nathan died shortly after the birth of his son. This son, Clarence, the first generation Canadian, helped run the shoe store that his father’s brother owned. As time went on, Clarence had his own family and, eventually, he was a grandfather. Clarence did not speak of his childhood or his father because it always made his mother sad but, every so often, he told the tale of his twin Uncles who, on their way to Canada from Russia, vanished.

Quickly, 100 years after Nathan’s death, a decade after Clarence’s death, his own great great grandchild, Sarah, knew this tale of her Great Great Great Uncles who went missing. Sarah decided to take a DNA test and, very suddenly, noticed a distant cousin with the surname Ross who also lived in Canada. This cousin’s tree seemed a bit spotty so Sarah sent a message to the distant cousin and explained her family tale of the lost Uncles.

The distant cousin match responded very suddenly. She was excited to have seen Sarah’s message because her ancestor was one of Clarence’s Uncles and he always talked about his brother that went missing. Her cousin who descended from one of the twins explained to Sarah that they changed their name to Ross to conceal their Jewish faith. She further explained that her ancestors thought their brothers vanished! Evidently, there was only a lack of communication during immigration and the brother’s never saw each other in Canada. They each had their own lives and their own families and because Sarah reached out, the brother’s descendants finally reconnected for the first time since leaving Russia nearly 150 years later.

Final thoughts

Regardless of how distant Ancestry, 23andMe, or any of the DNA websites list your DNA matches, it is your own due diligence to individually look over each match to determine whether or not the algorithm is correct. Within your “distant” cousins, you can uncover so much about your family. Collaboration is a huge step in finding out family mysteries, family secrets, and of course, building relationships and bringing distant family much closer.

About the Author