Not replying in full at this time, because I have 9 more Spanish Succession write-ups to go :P, but just pulling out the one part where I have something to contribute:
If that marriage had produced offspring, said offspring would have topped his father in genetic inbred-ness.
I'm...not convinced of this. The algorithm is complicated enough and their family trees complicated enough that I was unable to work out the math on the back of a napkin during lunch, but I would be surprised. I'm not saying it's impossible, but I would need to see a mathematical proof to believe it. Because from eyeballing it, it looks like the hypothetical offspring would be less inbred than Charles II.
Rationale:
Charles II had an inbreeding coefficient of 0.254. Source: this paper, where the numbers were computed using a database containing 3000 people, that ran to 16 generations of ancestry. (See also: things I couldn't do on the back of a napkin during lunch.)
That's slightly worse than if his parents had been siblings. (They were in fact most recently uncle and niece.)
Marie Louise's inbreeding coefficient was 0.078. Same source. Higher than the the average population, but less than one third of Charles's.
Furthermore, through the genealogical site that is Wikipedia, I've only been able to find two places where Charles II and Marie Louise's family trees merge. Their closest relationship to each that I found was first cousins once removed, through common descent from Philip III of Spain. And other than that, third cousins once removed through common descent from Ferdinand I, HRE.
That doesn't convince me that their offspring is going to be more inbred than the offspring of siblings.
Open to counterarguments and counterevidence, as always! (Either I missed some genealogical links between Charles and Marie Louise, which is possible, or when you work out the math rigorously, the final number is higher than I'm guessing, due to the sheer amount of inbred common ancestors.)
ETA: Building on my work last time, I calculated a value for the hypothetical offspring of Charles II and his first wife, based purely on the data set in the genealogy pasted in my original post. The problem is that the smaller your data set, the more likely you are to miss evidence of inbreeding. Since I can't go 16 generations back with 3,000 individuals, my numbers are too low.
However, I used my method on Charles II as a control, because we know a more accurate value for him based on a larger data set, and this is what I came up with:
0.18 for Charles, compared to a more accurate value of 0.254.
0.045 for hypothetical offspring.
So the more accurate value is surely higher, but not likely to be higher than 0.254, not if my method gets me a higher value for Mr. "My parents were uncle and niece and also first cousins once removed" Charles than for his "My parents were first cousins once removed and my mother wasn't all that inbred" offspring.
Caveat that when I learned this algorithm back when I was studying genetics, I didn't have to work it out on anything nearly as complicated as the Habsburgs, so I may be missing something and am open to corrections.
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timeasmymeasure
Re: Gossipy Sensationalist annotations
Date: 2021-05-17 09:34 pm (UTC)If that marriage had produced offspring, said offspring would have topped his father in genetic inbred-ness.
I'm...not convinced of this. The algorithm is complicated enough and their family trees complicated enough that I was unable to work out the math on the back of a napkin during lunch, but I would be surprised. I'm not saying it's impossible, but I would need to see a mathematical proof to believe it. Because from eyeballing it, it looks like the hypothetical offspring would be less inbred than Charles II.
Rationale:
Charles II had an inbreeding coefficient of 0.254. Source: this paper, where the numbers were computed using a database containing 3000 people, that ran to 16 generations of ancestry. (See also: things I couldn't do on the back of a napkin during lunch.)
That's slightly worse than if his parents had been siblings. (They were in fact most recently uncle and niece.)
Marie Louise's inbreeding coefficient was 0.078. Same source. Higher than the the average population, but less than one third of Charles's.
Furthermore, through the genealogical site that is Wikipedia, I've only been able to find two places where Charles II and Marie Louise's family trees merge. Their closest relationship to each that I found was first cousins once removed, through common descent from Philip III of Spain. And other than that, third cousins once removed through common descent from Ferdinand I, HRE.
That doesn't convince me that their offspring is going to be more inbred than the offspring of siblings.
Open to counterarguments and counterevidence, as always! (Either I missed some genealogical links between Charles and Marie Louise, which is possible, or when you work out the math rigorously, the final number is higher than I'm guessing, due to the sheer amount of inbred common ancestors.)
Re: Gossipy Sensationalist annotations
Date: 2021-05-19 07:08 pm (UTC)However, I used my method on Charles II as a control, because we know a more accurate value for him based on a larger data set, and this is what I came up with:
0.18 for Charles, compared to a more accurate value of 0.254.
0.045 for hypothetical offspring.
So the more accurate value is surely higher, but not likely to be higher than 0.254, not if my method gets me a higher value for Mr. "My parents were uncle and niece and also first cousins once removed" Charles than for his "My parents were first cousins once removed and my mother wasn't all that inbred" offspring.
Caveat that when I learned this algorithm back when I was studying genetics, I didn't have to work it out on anything nearly as complicated as the Habsburgs, so I may be missing something and am open to corrections.