what is the difference between 2nd cousin and 1st cousin once removed
In: Biology
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.
Latest Answers