Relationship/family tree question - need answer soon-ish

This stuff always confuses the heck out of me.

If Mary Lou and Betty Jean are sisters, how are their grandchildren related to each other?

Their children are first cousins, right? But what are the children of the first cousins…?

This chart seems to say “second cousins,” but I’m not 100% sure.


Second cousins is correct.

You can think of it this way (if it helps) - the common ancestor is Mary Lou and Betty Jean’s mother. Mary Lou and Betty Jean’s grandchildren are three generations away from the common ancestor. Subtract one, and that’s the “number” of cousin relationship, i.e. second. They have to be the same number of generations away from the common ancestor, and strictly speaking devoid of any complications like half-sibling relationships in the ancestral line.

Mary Lou’s children and Betty Jean’s grandchildren are first cousins once removed. The “removed” part deals with descendants who aren’t the same number of generations away from the common ancestor.

Sorry, that’s all a bit pedantic. It’s very clear in my head.

Yep, second cousins. Because? I say so. Why? I have literally dozens of these relations, they are everywhere I go. Seemingly no end of them, it’s exhausting.

As I understand it - if the number of generations is different:
Take the person with the least number of generations - that’s the cousin count. Difference in generations is the removal.

Mary Lou’s children would be first cousins with BJ’s children. So they would be first cousins once removed with BJ’s grandchildren, and first cousin twice removed with BJ’s greatgrandchildren… and vice versa.

ML’s grandchildren would be second cousins with BJ’s grandchildren
(and see above, 1st once removed with BJ’s children)
ML’s grandchildren and BJ’s great-grandchildren would be second cousin once removed. and vice versa. and so on…

The ambiguity with “X removed” is that it does not specify who is the one fewer generations from the common ancestor(s) the way uncle/niece does.

But then, many jurisdictions allow first cousin marriages, all(?) allow seconds. So at a certain point, this counting becomes less relevant. Plus I imagine in close villages in the good old days, beyond niece and nephew relations and first cousins, it became too convoluted and irrelevant to track with specific relationship names.

I agree with the nomenclature as presented above, but where I grew up, we’re just all cousins. Doesn’t matter what number or how far removed…and none of us are married to each other.

Thanks! Y’all are the best!

Exactly! Much like close villages in the good old days - too complicated and who cares?

Yep; #2, #3, #4 are correct. Half-siblings don’t matter except for the common ancestor(s) themsel{f,ves}. If the people are descended from different spouses of a common ancestor, I suppose they’d be ‘half-cousins’ though I don’t think I’ve ever heard the term used.

Suppose Adam Smith marries Alice Jones and and Adam’s sister Betty marries Alice’s brother Bob. The child of Alice & Adam will be ‘double cousins’ with the child of Betty & Bob. I suppose the grandchildren of those two couples would be ‘double 2nd cousins.’

Using the arithmetic formulae given in earlier posts, terms like ‘brother, sister, sibling’ can be obsoleted — just call yourselves ‘zeroth cousins.’ Aunt, uncle, nephew, niece —these are all ‘zeroth cousins once removed.’ (Following this model your father is your ‘minus 1’th half-cousin once removed’ though some might disparage this terminology as arithmetic run amok.)

My late husband’s parents were divorced. When his mom’s sister died, mom married her widowed brother-in-law. So my H and his first cousin became step-siblings when they were well into adulthood. When comparing notes with this cousin/step-sister’s daughter (still following?), we decided we were step-second-cousins-in-law. And left it at that.

My Grandfather and his brother married a pair of twins sisters. So I have ‘special’ double cousins. It’s not much different than regular cousins, in everyday life. My oldest brother has a huge Facebook ‘thing’ with all these cousins. I don’t do Facebook so I ain’t sure how it works, but he’s always telling me who’s getting married and who’s had a baby. I can’t EVEN keep it all straight. I gave up many moons ago.

If you want to take it a step further: Your parents are negative-second-cousins to each other, because they have an ancestor of degree -1 in common.

I feel like mentioning here that N. K. Jemisin and W. Kamau Bell are first cousins once removed. They are approximately the same age. (Apparently they share a family preference for an initial for a first name…)

Each of their wiki pages mentions the relationship, but it’s not made clear which of them is the grandchild of the common parents and which is the great-grandchild.

First cousins each get roughly 25% of their DNA from their common ancestor; how much they share could be as little as 0% or as much as that 25%. Considering how relatively inexpensive DNA tests are these days, perhaps it’s time to change those laws that prohibit first cousin marriage to make it dependent on DNA test results. I suppose the tests would have to be supervised, not the random mail-in kind.

It bothers me that removal can happen in two directions. There should be separate terms for that.

But in fact unless there’s a known problem (or some seem inherent in the family tree) the odds that their children would inherit anything detrimental would be fairly low. Even if they have 25% in common, their children would inherit 25% to 0% (average 12.5%). if the common genes were average, 12.5%, children of first cousins would have maybe on average 6.25% common genes.

I believe that bans on first-cousin marriage are in the minority. It’s generally allowed in the United States and most of the world.

Around these parts I figure 50% of the marriages are between distant cousins. Everyone seems to be related to each other. My Daddy moved us here later so my only blood relatives ( sibs) have all moved on. My Mothers family was small and has basically all died off. So I am positive I am not related to Mr.Wrekkers family. Everyone else is suspect, IMO.

It doesn’t come up in my tiny family, but in a large and complicated family I know, they’ve pretty much quit trying to map it all out. Non-immediate relatives become cousins, aunts/uncles, or nieces/nephews based on the age difference.

My formulation above, however perverse, had the property that people related only as A’th (Half-) cousins B-x removed had (1 + 2A + B + H) as their consanguinity degree, where H is 1 or 0 according as ‘Half’ is present or not. Yours deviates from this.

Here ‘consanguinity degree’ is **-**log[sub]2[/sub](probability of sharing rare gene).

I live in a densely-populated rural area with historically low mobility. Relationships can get intricate; it’s not unusual for people to be cousins on both father’s and mother’s side.

In Thai, words for sibling, child, grandchild and even great-grandchild are each single syllables. Nephew is a 2 syllable compound word: ‘child sibling.’ The word for 1st cousin is 4 syllables: it’s built up from the simpler words as ‘child sibling child sibling.’ Note that this could immediately lead to simple 4-syllable words for 2nd cousin (‘grandchild sibling grandchild sibling’) or even for 2nd cousin 1x removed. But when I try to explain to villagers that they’re 2nd cousin 1x removed with another villager (and tell them this new Thai word :smack: ) they look at me like I’m from Mars and say ‘Our word for that is not relatives.’

Yet in my inquiries I’ve never encountered an actual case of incestuous marriage — not even of 2nd cousins, let alone 1st.