that is absolutely not what selective breeding is
none of the habsurgs spouses have been selected for any of their traits
none of the habsurgs spouses have been selected for any of their traits
Why would you think that?
(rot13: gurl jrer nyy fryrpgrq, sbe gurve crqvterr)
Why else would XVII aristocracy have been so concerned with their family lines?
(as late as the XX, we can find fictional characters referring to Burke's Peerage* as "the stud book". I rather doubt that usage arises just because both were to use abbreviations and black type.)
* back in print! I guess the XXI is bound and determined, not only to repeat the mistakes of the XX, but also those of the XIX.
Just because they turned out to be in error about the value of their selections doesn't mean they hadn't been selectively breeding.
(an example in cattle: we had local bulls who had been bred for conformation for a long time, and luckily the breeders in the US instead were breeding for "liters of milk produced by the bulls' daughters", so now many [most?] locals inseminate with straws from the US lines)
While, yes, “good blood” was the social narrative, I think it was a lot more about institutional power (both wealth and connections) than what we would consider “genetic traits”.
At the moment, the best I can think of is to look at how important older ancestors were in a pedigree: if one cares only about institutional power, then one probably only cares about two* generations at most; if one cares about showing sustained evidence of good breeding, pedigrees would include ancestors who are dead and hence hold no temporal power whatsoever.
How does that sound?
* maybe 3 if you had a 15, 30, and 45 year old all as warlords in their own rights, but that's not a generic situation. My understanding is that the usual tenure was to have a single generation holding as much as possible, with the older generations retiring to monasteries to keep the land in the hands of military-age men.
EDIT: the balance of these concerns probably change between peace and war. https://en.wikipedia.org/wiki/William_the_Conqueror had trouble early in his career due to his illegitimacy, but by Nov 1066, he had a clear argument that, in matters of logistics and manoeuvre, he was puissant.
We'd look at the existence of things like “corruption of blood” as an imposed social consequences of non-compliance with institutions of social power and and how formally acknowledged vs. well-known but unacknowledged illegitimate children were treated and recognize that “blood” is really code for instititutional position (even if associated with a mythology of some kind of, more lamarckian than darwinian, inheritance as a rationalization.)
EDIT: upon reflection, I think we're talking about different things. I'd agree with you that the underlying, possibly hypocritical, calculations are done with an eye to current temporal power; I am trying to explore the models they used and how they attempted to frame realpolitik-based decisions in socially-acceptable manners.
Consider realpolitik in The Republic, where it's explicitly stated that the gold, silver, bronze races are a convenient fiction and there has to be movement between them; in 1984, where it's explicitly stated that IngSoc (and the others) are all pure meritocracies in principle and practice, but there's still not much social movement; in the language of US mobsters "cut in the smart boys from the opposition, so that they can't set up a racket of their own."; in the language of marxists "utilization of potential leadership cadres from historically superseded classes"; and in the language of Vilfredo Pareto "capture of the rising elite".
(last three examples were st^H^Hliberated from Linebarger: https://www.gutenberg.org/files/48612/48612-h/48612-h.htm )
I maintain that they understood breeding domestic animals very well, and they tried their best, with the resources they had, to selectively breed "better" (aristo) people. (Much of feudalism makes way more sense if you start with the axiom that human society should reflect barnyard large domesticate societies) Even we don't know what would be "good genes" for being a successful warlord, so their approach of looking at past performance and hoping for future results (a noble is someone whose family has exclusively extracted rents for a certain number of generations; a royal is someone whose family has sat upon a throne) seems reasonable to me.
In particular, Charles II (like the Ptolemies and Cleopatras of Egypt: https://en.wikipedia.org/wiki/Ptolemaic_dynasty#Family_tree ) has clearly been line bred. (He is his own cousin — in multiple ways. We might quibble over the distinction between line- and inbreeding, but [a] I was trying to be charitable to the Habsburgs, and [b] I don't think that distinction is relevant to this discussion, so I'm happy to call anyone with too few ancestors "linebred")
If you think people would do better with early-20th century Eugenics than aristocratic societies have done over the last thousands of years, we can have that discussion, but I think it's a different one than I had intended. Along those lines, see https://news.ycombinator.com/item?id=39681181 for the problems I would be likely to bring up.
Does that make sense?