If you can't keep your second 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.
Family reunions are often filled with confused people scratching their heads, ticking off fingers and mumbling, "If my mother's aunt was her father's grandmother, then what does that make us?" The more steps there are connecting two relatives, the harder it can be to decipher.
What is a cousin?
To understand the terms of an extended family tree, it is useful to begin with the basics. The term "ancestor" refers to people who share a direct line, according to the journal PLOS Genetics. Examples of these are your parents, grandparents, great-grandparents etc. Ancestors don't include the siblings of these people. This means that while uncles and aunts (the siblings of a parent) are blood relatives, they don't count as ancestors.
Other than aunts and uncles, any other blood relative that isn't an ancestor is a cousin of some sort. The most common use for the term "cousin" is to refer to a first cousin. This is the child of your uncle or aunt.
What is a second cousin?
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.) denotes the number of generations between two cousins’ parents and their nearest common ancestor.
Click on the arrows in the image below to see where a second cousin is positioned on the family tree:
When does a cousin become "removed"?
The term "removed" refers to the number of generations separating the cousins themselves, according to ancestry.com (opens in new tab). So your first cousin once removed is your parent's first cousin, or the child of your first cousin. Your second cousin once removed is the child of your second cousin or the parent of your third cousin. And your first cousin twice removed is the grandchild (or grandparent) of your first cousin or the cousin of your grandparent.
Clearly, it doesn't take many generations before your family tree is a bit unwieldy. Case in point: In 2007, it was revealed that vice president Dick Cheney and presidential hopeful Barack Obama are eighth cousins. Cheney's wife, Lynn Cheney, discovered this tidbit while researching her husband's genealogy for a memoir she was writing, the BBC reported (opens in new tab).
Parallel vs cross
If these distinctions aren't confusing enough, first cousins can be further parsed into parallel and cross cousins. Parallel cousins are the children of same-sex siblings, according to the journal American Anthropologist (opens in new tab) — for example, the children of your mother's sister are your parallel cousins. Cross cousins are the offspring of opposite sex siblings, such as your mother's brother's children, or your father's sister's children.
And in case you were wondering, the two relatives at the family reunion (A's mother's aunt is B's father's grandmother) are second cousins once removed.
Find out about the evolution of families and marriages in this book by SAGE Publications (opens in new tab). Want to explore your own family tree? Websites such as ancestry.com (opens in new tab) allow you to trace your lineage.
"What is ancestry?". PLOS Genetics (2020). https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1008624 (opens in new tab)
"Complementarity and the Structures of Parallel-Cousin Marriage". American Anthropologist (1986). https://www.jstor.org/stable/679082 (opens in new tab)