7.1 Many sites on the internet will take a stab at explaining double cousins, which is to say, double 1st cousins…of those that go onto double 2nd cousins, most (but not all!) realize there are 2 different kinds…reviewing Charts 11 and 12 below. Only one I’ve found adds the third kind…well, actually let’s call it the third basic kind. Some folks include double-half cousins as another kind…as well as the offspring of identical twins, which are genealogically cousins, but genetically much more closely related…something we’ll get into in 2 weeks.
7.2 But really, double half-2nd cousins are not double 2nd cousins…and more than a half-brother is a full brother…so Chart 18 diagrams the third kind, what I call Sesquilineal double 2nd cousins. Sesqui- means one and a half, most commonly encountered in the word sesquicentennial, a 150th anniversary. And this kind is sort of half-way between uni- and bi-…a hybrid if you will.
7.3 But before anything else, we should verify that Abner and Zeke are indeed 2nd cousins 2 ways. As you can see, they’re father’s are 1st cousins, since those grandfathers are brothers…way 1, check. And Abner’s mother is a sibling of Zeke’s father, since those grandmothers are sisters…way 2, check. The question is, what exactly is going on here? Below, I’ve redrawn the charts to highlight a particular feature which will provide the answer.
7.4 In Chart 18-A, Zeke’s father X is a 1st cousin to Abner’s mother C…the mothers of X and C are sisters. In Chart 18-B, I’ve juggled things around to show that Zeke’s father X is also a 1st cousin to abner’s father B…X and B have fathers who are brothers. But here’s the key: these 2 cousins of X‘s are on different sides of X‘s family…B on his father’s side, C on his mother’s side. B and C are not related to each other…they are cousins to X on opposite sides of X‘s family…and we all have, unless a parent is an only child, 2 sets of unrelated 1st cousins…children of our father’s siblings and children of our mother’s siblings.
7.5 Looked at from the point of view of B and C, they happen to share a 1st cousin…but they share nothing else…no aunts, uncles, or grandparents in common. Now from where Abner sits, his father’s uncle married his mother’s aunt…unusual, but again, this uncle and aunt are not related. And from Zeke’s viewpoint, one of his father’s paternal cousins married one of his father’s maternal cousins…cousins on opposite sides of his father’s family…as seen in Chart 18-C, rearranged yet another way.
7.6 Similarly, the 3 ways of being double 3rd cousins diagrammed in Chart 17 can be expanded to 6 ways, in Chart 17-A. Once again, notice the “crossover”…now it’s split between 2 different generations. And if you were to move Abner and Zeke up into the position of their parents’ generation, you would have the corresponding double 2nd cousins versions…uni-, bi-, and sesqui-lineal. So far, I don’t have names for all these double 3rd cousins arrangements…and there’ll be even more, for double 4th cousins and so on…maybe someday!
7.7 Now technically speaking, there is a fourth way you could have double 2nd cousins…but I don’t count it, and for a very important reason. When analyzing kinship connections, I take the relationships that are given to be as such…and by that I mean, these relations exist but no others. For example, if Abner and Zeke are 1st cousins, and Alice and Zelda are 1st cousins, I assume they are related in no other ways…each is related to his or her cousin by a CR of 1/8. Were Alice and Zelda double 1st cousins, it would be 1/4…twice as close as Abner and Zeke…but if that’s not stated, that’s not assumed.
7.8 Thus the 4th way to have double 2nd cousins is if single1st cousins were to marry each other. In this case, Abner’s father and Zeke’s mother are 1st cousins…so the boys are 2nd cousins one way…but also Abner’s mother and Zeke’s father are 1st cousins, so they are 2nd cousins a second way. Trouble is, they are also siblings. Their CR is not that of double 2nd cousins…1/32 + 1/32 = 1/16…but instead 1/32 + 1/32 + 1/2 = 9/16. That these “four” parents are actually the same 2 individuals doesn’t matter…CRs are cumulative…another word for it is “additive,” which means you add them together.
7.9 Reminds me of a bar bet…Abner and Zelda are 2nd cousins…both are of legal age and neither is married. In all 50 states 2nd cousins can get married, but Abner and Zelda cannot…why not? The answer of course is that they’re also siblings!
7.10 And this gets around to why sibling marriages are frowned on…the offspring are not only siblings, but double 1st cousins…CR of 1/2 + 1/8 + 1/8 = 3/4. You’ve heard I’m sure that such inbreeding results in offspring that are “too closely related.” Now you know how much is “too close”…busy bees, nez pah? Next week, cousins who aren’t your cousins…because they’re removed…peace out…
So anywho…last week I showed you what Abner and Zeke looked like…what about Alice and Zelda? Why not…just be careful what you ask for, that’s all’s I’m sayin’…
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