#145: How Close Is Close?

145.1 …not very close, as it turns out. It’s one thing to say 1st cousins are related by 1/8, and 2nd cousins by 1/32…but how close is that really?  How big are 1/8 and 1/32 when compared to say 1/1,000,000 (a millionth)? Here’s where percentages come in real handy.

145.2  Let me pose a question…at what point (1st cousins, 2nd cousins, halfs, removeds, etc.) are 2 relatives 1% related and 99% unrelated? What would you say…5th, 6th, 10th, 20th cousins? If you consult Chart 503*, you will see that the 99% threshold is crossed relatively early on…at 3rd cousins. And perhaps surprisingly, even 1st cousins are within 2½ percentage points of being 90% unrelated.

* If this chart looks familiar, it is Chart 485 from Related How Again? #140, with siblings and half-siblings added at the top in blue…for comparison to the degrees of cousins. And since I brought it up, the one millionth is passed at half-9th cousins or equivalent.

chart 503

145.3  I hope now you can grasp why 5th cousins, unrelated by 99.95%, are for all intents and purposes (and especially genetic ones) as closely related as 2 random people off the street. And I am finding that when a person wonders how closely related they are to somebody else…over and above mere curiosity…it often has to do with someone they are romantically interested in. Perhaps they just met, or have been dating for a while, or are married, with children even…and they discover there is a family connection way, way back.

145.4  It is safe to say that in general, a relationship you didn’t know about is one that has no real relevance to whether you should or shouldn’t be together. Certainly not in a legal sense…nothing beyond 1st cousins is unlawful anywhere in the US, and in the vast majority of cases, a person knows who their 1st cousins are. Grown-up adoptees are a major exception of course, which is why siblings are often “kept together.”

145.5  As far as the “ick” factor is concerned, many people today are a lot more squeamish than folks were just a few generations ago, when as close as 1st cousins marrying was relatively common. Even more troubling today is the tendency in the old days for foster siblings or even guardian & ward to get together, to the approval of all concerned. So if 10th cousins freaks you out, despite the “99.999995% unrelated” you find on Chart 503, I don’t know what I could say to change your mind.

145.6  But here are the latest such questions from this website wiseGEEK, and my answers to them there verbatim.

chart 504

145.7  Since you mention that your grandmother had half-siblings from Bill’s first wife, and you also wonder if your husband might be your “half cousin,” I will assume that Bill’s first wife is your husband’s great great grandmother. In that case you and your husband are half-2nd cousins once removed. This also means you are a half-2nd cousin to one of your husband’s parents. 

About half the states allow marriage between 1st cousins, and all allow marriage between 2nd cousins. You are more distant than that, so you are completely legal. Still, I understand that “half-2nd cousins once removed” might sound close enough to be wrong in your mind. After all, “2nd cousins” sounds close compared to 8th cousins or 10th cousins, right?

So how close are you? By way of comparison, 1st cousins are related by 1/8. In terms of percentages, that’s 12.5%. It’s a quarter of that for 2nd cousins, so about 3.1%. For half-2nd cousins once removed it’s a another quarter, or .78%. This means that you and your husband’s genes are .78% the same and 99.22% different. Yes, you and your husband are related to a small degree, but you are over 99% unrelated. Not very close at all, is it?

chart 505

145.8  There is a mistake in your description of your family. You are correct in saying that your mother Miriam and Christy are 1st cousins, since their mothers Milena and Eless are sisters. But you are wrong in saying that Miriam and Christy are also 1st cousins to Alan. Instead, they are 2nd cousins to Alan, since Alan’s father Phil is 1st cousin to Milena and Eless. 

You are a 2nd cousin of Joe, since your mother Miriam and Joe’s mother Christy are 1st cousins. But you are also a 3rd cousin to Joe, since your mother Miriam and Joe’s father Alan are 2nd cousins. Thus you are related to Joe two ways: 3rd cousin (1/128) and 2nd cousin (1/32 = 4/128) for a total degree of relationship of 5/128.

It is easier to see how distant this is if we convert the fractions to percentages. You and Joe are 3.9% related and 96.1% unrelated. Nowhere in the US are relatives beyond first cousin forbidden by law to marry, which is 12.5% related and 87.5% unrelated, so you’re in the clear legally. And yes, Jeff has nothing whatsoever to do with any of this!

chart 506

145.9  To figure out relationships like this, take it one step at a time. I suggest after each step, stop a moment and think about where you are. And remember, practice makes perfect!

Step 1: What is your grandfather’s niece? It is your parent’s 1st cousin, the child of your grandfather’s sibling.

Step 2: Your parent and your parent’s 1st cousin each have a child. Your parent’s child is you. Your parent’s 1st cousin’s child is this guy’s parent, since your parent’s 1st cousin is this guy’s grandmother.

Step 3: You and this guy’s parent are 2nd cousins, since you two are the children of 1st cousins.

Step 4: This guy is the child of your 2nd cousin, thus you are 2nd cousins once removed. 

Genetically, 2nd cousins once removed are 1/64 related, that is, related by 1.56 percent, and unrelated by 98.44 percent. And that’s pretty distant, I think you’ll agree. 

 145.10  Next week…does Connelly, Burke, Gargan & Fitzgerald  have any significance to you? Could it be a law-firm? Or are you confusing it with Nixon, Mudge, Rose, Guthrie, & Alexander  perhaps?


Copyright © 2013 Mark John Astolfi, All Rights Reserved


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