what is the difference between 2nd cousin and 1st cousin once removed
In: Biology
Your first cousin once removed is the parent of your second cousin.
“Removed” is the difference in generations between you and the relative. So, anyone “once removed” is part of your parents’ generation of the family.
A second cousin means you share great grandparents as your most recent common ancestor
A first cousin once removed means that either your first cousin is their parents, or your parents are their first cousin.
Xth cousins means you need to go X generations up from their parents to reach a common ancestor. Your first cousins have a common an ancestor the next generation up from your parents (your grandparents) to reach a common ancestor. 2nd cousins require you go up 2 generations from their parents to reach a common ancestor (your great grandparents)
Cousins Y times remove means you are Y generations apart. You are on the same generational step as your cousins, but their children will be another step lower, thats the once removed. From a 1st cousin once removed, the one from the older generation only has to go up one step from the parents to reach a common ancestor (their grandparents) but the one from the younger generation has to go up two steps from their parents to reach that same common ancestor (their great grandparents) so we take the smaller number (one generation up from the parents) and thays out X, and the difference between the two numbers (2-1=1) and that’s our Y
And thus also means cousinhood is also always mirrored, so if A is B’s first cousin once removed, B is also A’s first cousin once removed.
Some weird implications of this, your siblings are your 0th cousins, your parents are your 0th cousins once removed, and you are your own negative first cousin.
The # before cousin and the # before removed are completely different things. The first one is all about the number of generations between you, the other person in question, and your closest common ancestor, which we’ll call CCA. If your CCA is your parents, you’re siblings. If your CCA is your grandparents, you’re 1st cousins. If your CCA is your great grandparents, then you’re 2nd cousins. And so on. It’s very simple if the people you’re comparing (you and your cousin in this example) are in the same generation.
But what if they aren’t in the same generation? What if the CCA is your grandmother but the other person’s great grandmother? That’s where # removed comes into play. So let’s say your first cousin, the child of your uncle, has a kid? What is that kid to you? The CCA, in this case, is still that same set of grandparents as your first cousin. That means that your cousin’s kid is also your first cousin. But they’re a generation down the chain, so you add the Once Removed label to show that you’re not in the same generation. And if that same First Cousin Once Removed has a kid? Well then you’ll be sending a baby gift to your First Cousin Twice Removed.
Unless you’re some type of royalty, I wouldn’t waste much brainpower on anything beyond 2nd cousins and Twice Removals because it probably isn’t relevant. The better term for anyone beyond that is probably “stranger”.
If your first cousin once removed is your parent’s cousin, their child is your second cousin.
(if you first cousin once removed is your cousin’s child, their child is your first cousin twice removed)
I’ll try to give you a more general answer than the others here:
Think of [X] cousin as the ***minimum*** degree of separation between two people and their common ancestor.
* 0th cousin: the closest person in common is a parent to at least one
* Parent to both: “siblings”
* Parent to one, grandparent to another: niece/nephew & aunt/uncle
* Parent to one, great-grandparent to another: grand niece/nephew & great aunt/uncle
* and so on…
* 1st cousin: the closest person in common is a grandparent to at least one
* 2nd cousin: the closest person in common is a great-grandparent to at least one
* and so on…
If the distance to the common ancestor is the same, for 1st and above we just say “[x] cousin” and that’s it.
If the distance to the common ancestor is NOT the same, then the “[y] removed” is the ***difference*** in distance between the two.
* 1st cousin once removed: the common ancestor is a grandparent to one, and great-grandparent to the other
* 1st cousin twice removed: the common ancestor is a grandparent to one, great-great-grandparent to the other
* 2nd cousin once removed: the common ancestor is a great-grandparent to one, great-great to the other
* and so on…
And, while this applies to my family, it doesn’t fully apply to all. For example, due to connections to rural China, my wife has a first cousin who is also a second cousin once removed via another family connection. She also has a second cousin who is also a third cousin via another family connection. Whenever that happens, people tend to use the term reflecting the closest cousin connection, and if more than one at the same level, the closest “removed” connection.
I have two sisters, who married first cousins.
Each sister’s children are first cousins through their mothers.
Each sister’s children are second cousins through their fathers.
Each sister’s children are the nephews and nieces of the other sister’s husband.
Each sister’s children are the first cousins once removed of the other lot’s father.
Your “level” of cousin is determined by your closest common ancestor. If you share a grandparent: first cousins. If your closest ancestor is a great-grandparent: second cousins. However, your grandparent might be a younger relatives great-grandparent, or vice versa. In this case your “level” of cousin is determined by who is closest to the common ancestor. And the difference between how far the two of you are if your level of “removed.”
So if your closest ancestor is your great, great grandparent, but is their grandparent, you will be first cousins, since they are only two away from the common ancestor. And since your common ancestor is your great, great grandparent, that makes it “twice removed.” So they would be your “first cousin, twice removed.”
https://www.ancestry.com/c/dna-learning-hub/cousins-dna-match
Your parents’s siblings are your aunts and uncles. Your aunts and uncles’ children are your first cousins.
Your grandparents’ siblings are your great aunts and great uncles. Your great aunts/great uncles’ children are your parents’ first cousins, and your first cousins once removed. The children of your first cousins once removed are your second cousins.
Many have already answered, but I find [this video](https://youtu.be/PM79Epw_cp8?si=C5cj_uCRAeQV1kKX) from CFP Grey helpful.
Basically, the difference is whether you or your child is being spoken of.
As you know, your first cousin is the child of your parent’s sibling (your aunt or uncle). If your first cousin has a child, that child is your first cousin, one generation removed. The removed cousin takes the lowest applicable cousin number and the number of generations they are from you.
Let’s take the same situation as above; except now both you and your first cousin have children. Basically, those children are second cousins to each other because their parents are first cousins. If these two second cousins each have children of their own, those children will be third cousins.
Here are a few rules of thumb to help you keep things straight:
1. Cousin numbers indicate the number of “Gs” in the title of their earliest shared common ancestor. For example, two FIRST cousins will share a Grandparent; two SECOND cousins will share a Great-Grandparent; two THIRD cousins will share a Great-Great-Grandparent; etc.
2. If you have a removed cousin, the cousin number PLUS the removed number will equal the lowest cousin number for your descendants to the removed cousin. For example, if you have a first cousin (1) once removed (1), your child will be a second cousin to the removed cousin (1+1=2). If your first cousin once removed has a child, they are your first cousin (1) twice removed (2), and your grandchildren would be child’s third cousin (1+2=3).
[Here’s](https://youtu.be/PM79Epw_cp8?si=SwLBUL1QIMBev8oH) a video that explains it pretty well.
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