Who is called first cousin?

The term “first cousin” refers to the children of someone’s aunt or uncle. Specifically, your first cousins are the children of your parent’s siblings. So the children of your mother’s sister or brother are your first cousins on your mother’s side. And the children of your father’s sister or brother are your first cousins on your father’s side. First cousins share a common set of grandparents. You and your first cousins have the same grandmother and grandfather on one side of the family.

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Key Facts About First Cousins

First cousins are the children of someone’s aunt or uncle.
Your first cousins are the children of your parent’s siblings.

First cousins share a common set of grandparents.
You and your first cousins have the same grandmother and grandfather on one side of the family.

Some key questions about first cousins include:

Questions About First Cousins

What is a first cousin?
What is the relationship between first cousins?
How are first cousins related?

Do first cousins share grandparents?

Let’s explore the answers to these questions in more detail.

What is a First Cousin?

As mentioned, a first cousin is the child of someone’s aunt or uncle. Specifically:

Your first cousins on your mother’s side are the children of your maternal aunts and uncles.
Your first cousins on your father’s side are the children of your paternal aunts and uncles.

So your mother and father’s siblings each have their own children. And those children are your first cousins. For example:

Your mother’s sister’s children are your first cousins on your mom’s side of the family.
Your father’s brother’s children are your first cousins on your dad’s side.

The “first” in first cousin indicates that these cousins are the closest cousins you have. First cousins are distinguished from second cousins, third cousins, and so on. Second cousins would be the children of your parents’ first cousins.

Some key facts about what a first cousin is:

Key Facts on What a First Cousin Is

A first cousin is the child of your aunt or uncle.
Your first cousins are the children born to your parents’ siblings.

“First” indicates these are your closest cousins.
First cousins are distinct from second, third, etc. cousins.

So in summary, your first cousins are simply the children of your aunts and uncles. They are your closest cousins in the family tree.

The Relationship Between First Cousins

The relationship between first cousins is that you share a common set of grandparents. Your parents are siblings, meaning they have the same parents. And you and your first cousins have those same shared grandparents.

Specifically:

You and your first cousins on your mother’s side share your maternal grandparents.

You and your first cousins on your father’s side share your paternal grandparents.

This means you and your first cousins are part of the same extended family. You’re both in the same “branch” of the family tree.

You could visualize the relationship between first cousins in this way:

You	Your parent	Your aunt/uncle	Your first cousin
You	Your mother	Your mother’s sister	Your first cousin (aunt’s child)

In this example, your parent and your aunt/uncle are siblings. They share the same parents as one another and as you. So you and your first cousin are part of the same family branch and share grandparents.

Some key facts about the relationship between first cousins:

Key Facts on the Relationship Between First Cousins

First cousins share a common set of grandparents.

Your parents are siblings with your aunt or uncle.
You and your first cousins are part of the same family branch.
You share the same grandparents on one side of the family.

So in summary, first cousins have a close familial tie of shared grandparents and position within the extended family tree. You’re connected through one generation to the same lineage.

How are First Cousins Related?

First cousins are related by being the children of siblings. Specifically:

Your mother’s sister’s children are your first cousins on your mom’s side.

Your father’s brother’s children are your first cousins on your dad’s side.

This means first cousins have parents who are siblings. To visualize how first cousins are related:

You	Your parent	Your aunt/uncle	Your first cousin
You	Your father	Your father’s sister	Your first cousin (aunt’s child)

In this example:

Your father and his sister share parents.
You and your cousin share grandparents (on your dad’s side).
Your fathers’ sibling relationship makes you and your cousin first cousins.

Some key facts on how first cousins are related:

Key Facts on How First Cousins Are Related

First cousins have parents who are siblings.
Your parent and your aunt/uncle share parents.

You and your first cousin share grandparents on one side.
Your parents’ sibling relationship makes you first cousins.

So first cousins are related by being the children of siblings. You’re connected by one generation through your shared grandmother and grandfather.

Do First Cousins Share Grandparents?

Yes, first cousins always share a common set of grandparents. Specifically:

You and your first cousins on your mom’s side share your maternal grandmother and grandfather.
You and your first cousins on your dad’s side share your paternal grandmother and grandfather.

This is because first cousins have parents who are siblings. And those siblings (your parent and aunt/uncle) share the same parents as each other. Visually:

You	Your parent	Your aunt/uncle	Shared grandparents	Your first cousin
You	Your father	Your father’s brother	Your paternal grandparents	Your first cousin (uncle’s child)

So you and your first cousin are both grandchildren of your shared grandparents. This is the definitional blood relationship of first cousins.

Some key facts about first cousins sharing grandparents:

Key Facts on First Cousins Sharing Grandparents

First cousins always share a set of common grandparents.
You share your maternal grandparents with your first cousins on your mom’s side.
You share your paternal grandparents with your first cousins on your dad’s side.

You’re both grandchildren of those same grandparents.

In summary, having a shared grandparent connection is inherent in what makes you and your first cousins related. This grandparent relationship is what defines first cousins.

Other Questions About First Cousins

Some other common questions about first cousins include:

Can You Marry Your First Cousin?

In most states in the U.S., it is legal to marry your first cousin. However, there are some states that prohibit marriage between first cousins. Globally, opinions are divided on whether first cousins should marry. Some cultures approve of first cousin marriages, while others prohibit it.

Those opposed believe marriage between first cousins leads to higher risk of congenital defects in children. Proponents argue this risk is small and not a good reason to prohibit cousin marriages. Cousin marriage remains a controversial issue, but it is legal in much of the U.S.

What is a First Cousin Once Removed?

A first cousin once removed is the child of your first cousin. So your first cousin’s son or daughter is your first cousin once removed. This person is one generation below you and your first cousins. Visually:

You	Your first cousin	Your first cousin’s child
You	Your first cousin	Your first cousin once removed (your cousin’s child)

The “once removed” indicates there is a one generation difference between you and your cousin’s child. Your cousin’s kids are your first cousins once removed.

How Much DNA Do First Cousins Share?

On average, first cousins share about 12.5% of their DNA, but it can range from 7-14%. First cousins have 25% of DNA from shared grandparents, but only pass down half to their kids. Compared to other relationships:

Relationship	Amount of shared DNA
Parent/child	50%
Full siblings	50%
Half siblings	25%
First cousins	12.5% (average)

So while you share grandparents with first cousins, only around 12.5% of your actual DNA overlaps since you each inherit different combinations from grandparents.

Differences Between First, Second, and Third Cousins

The differences between first, second, and third cousins are:

First cousins – Your parents are siblings
Second cousins – Your grandparents are siblings
Third cousins – Your great-grandparents are siblings

Some key differences:

Relationship	Shared ancestors	Generational difference	Amount of shared DNA
First cousins	Grandparents	1 generation	12.5% (avg.)
Second cousins	Great-grandparents	2 generations	3.13% (avg.)
Third cousins	Great-great grandparents	3 generations	0.781% (avg.)

So the increasing numerical cousin terms reflect increasing generational differences between you and the most recent shared ancestor.

Conclusion

To conclude, first cousins are the children of your aunts and uncles. They are your closest cousins. You share the same grandparents on one side of the family. Your parents are siblings with your aunt or uncle. This makes you first cousins with their children through this shared grandparent relationship. First cousins have a special family connection and legal ability to marry in much of the U.S. Understanding the first cousin relationship provides insight into how extended families are structured.