What is a third cousin? Are third cousins genetically related to you? How many third cousins do you have? Find answers to these questions and more in this post.
Most of us don’t grow up knowing our third cousins very well, unless we live in places where we have lots of distant extended family living all around us.
This is why it is no surprise that people want to know more about third cousins and exactly how they are connected on their family tree.
Note: You will find that a genealogical third cousin is often different than a third cousin DNA match: What is a Third Cousin DNA Match?
What is a third cousin?
Third cousins share at least one great-great grandparent, and are descended from different offspring of those great-great grandparents. To put it another way, your great-grandparent and your third cousin’s great-grandparent were siblings.
Visual explanation of third cousins
Sometimes it is easier to understand a visual explanation. It can be tough to keep all of the greats and the great-greats in order in our head!
In the image below, we can see see descendants of Peter and Earlene.
As you can see, the children of Peter and Earlene are siblings, their grandchildren are first cousins, their great-grandchildren are second cousins, and their great-great-grandchildren are third cousins.
Are third cousins considered distant cousins?
Third cousins are not technically considered to be distant relatives. A distant relative is someone who is more distantly related than a third cousin.
One possible criteria that people may use to determine whether they consider someone to be a close or distant relative may be whether they knew their common ancestor personally.
As you know, third cousins share great-great grandparents, but their parents shared great-grandparents. Since the second cousins (the parents of the third cousins) may have known their common ancestor personally (their great-grandparents), they are more likely to raise their children to know their more extended family.
I have a few second cousins on my dad’s side of the family who I knew fairly well growing up. They have their own children now, as do I.
While geography separates us, I expect that someday soon our children will meet each other. They will play and have fun, and hopefully , grow up with fond memories of their third cousins.
What is a third cousin once-removed?
A third cousin once-removed is the child of your third cousin or the third cousin of your parent.
“Cousins removed” can be a confusing concept, especially if you are new to the idea. It’s not too difficult to calculate how whether you are third cousins or third cousins “removed”, however.
First, make sure that you are really third cousins (and not more closely related). Is the person most closely descended from the common ancestor a great-great grandchild of the ancestor?
Then, calculate how many generations the other person (i.e. you, or the other cousin) is from the MRCA (most recent common ancestor), and subtract four.
For example, if you are six generations away from the most recent common ancestor, you would subtract six from four (the number generations the third cousin is from the MRCA). The answer (two) is the number of generations removed you are from your third cousin.
In this example, you and your cousin are third cousins twice-removed.
What is a half-third cousin?
A half-third cousin is technically a third cousin who shares only one great-great grandparent with you instead of two. This type of situation occurs most frequently when the great-great grandparent’s spouse remarried after the death or divorce of their first spouse.
If the great-great grandparent had a child with their first spouse and then has a child with their second spouse, their children are half-siblings. Their grandchildren would be half-first cousins, their great-grandchildren half-second cousins, and finally, their great-great grandchildren would be half- third cousins.
How many third cousins do I have?
On average, we can expect to have about 190 third cousins. This is assuming that the average family has 2-3 children and those children grow up to have 2-3 children, etc.
The exact number of third cousins that you actually have will depend on how many children all of your great-great grandparents had and how many survived to adulthood and began their own families, as well as:
- cultural traditions related to family size
- political and economic situations
It would be very difficult to know the names of all of your third cousins, much less meet all of them personally. However, since third cousins are not considered to be distant cousins, it is a worthy goal to at least know who all of them are.
Are third cousins genetically or blood related?
Third cousins are always considered to be relatives from a genealogical perspective, and there is about a 90% chance that third cousins will share DNA.
With that said, third cousins who do share DNA only share an average of .78% of their DNA with each other, according to 23andMe. The exact amount of shared DNA between third cousins can vary, but it is rare for third cousins to share more than 2%.
I hope that this post has helped you understand more about third cousins, exactly how you are related, and how many third cousins you might have out there in the world.
If you have any questions about something that you read in this post, or if you would like to share your own experience learning about your third cousins, I would love to hear from you in the discussion below.
Thanks for stopping by today – you are awesome!