For example:. However, keep in mind that this trick only works if you are both the same number of generations removed from the common ancestor. Sometimes you and your cousin may share a common ancestor,but you each call this ancestor something different.
The number before "removed" will always represent the number of generations you are separated "removed" from the cousin. You, your siblings, and your first, second,and third cousins are all of the same generation. This is because your parents and their generation are 1 above yours. This pattern continues throughout each generation. If you can't keep your third cousins and your first cousins twice removed straight, you are not alone. But there's a simple way to figure out the relationships between relations.
First cousins share a grandparent, second cousins share a great-grandparent, third cousins share a great-great-grandparent, and so on. The degree of cousinhood "first," "second," etc. That puts you at 68 billion ancestors around AD. With a concept called pedigree collapse , which is what happens when people end up with a mate who is somewhat or very closely related to them. So for example, if two cousins had a child, that child would only have six great-grandparents, not eight.
The reason for this is that for most of human history, people spent most of their lives in the same five mile radius, and the other people in that same area tended to be immediate and extended family. So that group of 4, people above? Because of pedigree collapse, if you extended your family tree way, way back, it would begin to get smaller , resulting in a diamond shape:. The widest point of the Ancestor Cone happens for most of us around AD , when our family tree is near the total world population at the time.
From that point on, pedigree collapse becomes a stronger factor than the normal upward x2 multiplier, and the tree converges inwards. The simplest way to think about it is that every stranger in the world is a cousin of yours, and the only question is how distant a cousin they are. The degree of cousin first, second, etc. For first cousins, you only have to go back two generations to hit your common grandparents.
For second cousins, you have to go back three generations to your common great-grandparents. Since a lot of people get confused about cousin definitions, I made a little chart illustrating what a second cousin is. So notice that for you and your second cousin, A your parent is a first cousin of their parent, B you have grandparents that are siblings, and C their parents are your common great-grandparents.
For third cousins, everything just goes up a level—your parents are second cousins, your grandparents are first cousins, your great-grandparents are siblings, and you have a common pair of great-great-grandparents. A straight second, third, or fourth cousin must be on your same generation level. This is assuming that the average family has children and those children grow up to have 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:.
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. There are two excellent ways to discover how many third cousins you have. First, you could take an Ancestry DNA test to receive a list of genetic relatives and their estimated relationship to you. You could also start building your family tree check out my book on Amazon on how to do it.
Since our third cousins are descended from our great-great grandparents, we need to build a family tree. If you want to get a subscription to make things a little easier, I recommend it. With that said, third cousins who do share DNA only share an average of.
Since third cousins share only a very small percentage of their DNA, there is no issue with third cousins dating from a genetic perspective. According to an article by The Spruce, marriage between second cousins and more distant cousins is legal throughout the United States. As you know, third cousins share the same great-great grandparents. The common ancestor shared between Queen Elizabeth and her husband, her third cousin, was Queen Victoria. Other famous third cousin marriages include John Adams, second president of the United States, and his 3rd cousin, Abigail Smith.
There is even some evidence that Thomas Jefferson was third cousin to his wife, Martha Wayles Skelton. I was unable to find a country in the world that has a legal prohibition to third cousin marriages, as there is really no good reason to prevent them.
In many communities, third cousins may marry without even knowing that they are third cousins. 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. This site uses Akismet to reduce spam. Learn how your comment data is processed. Hi Maria, You are second cousins once-removed to your son's third cousin. This is because you are one generation closer to your shared common ancestor, your son's great-great grandparent i.
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