A recent question on our sister site made me wonder about something: where does the standard system of distinguishing different types of cousins in English via degrees and removals (as in "Nth cousin K times removed") originate? Did English borrow it from another language, and if so, how far back can we trace it? Did it develop out of an earlier, simpler and/or less regular system, and if so, when, where and by whom?
A quick web search did not turn up a clear answer. I'm finding a lot of resources explaining how the system works, like this Q&A thread here and this Wikipedia page, but not where it comes from or why it works the way it does.
FWIW, this system has a number of features that make me suspect that it was likely deliberately invented (or formalized) for genealogical use:
- It's verbose, and thus good for formal documents but not for casual use. Nobody's going to use it in casual speech to address their relatives ("Hey, second cousin once removed, nice to see you!") the way closer and shorter kinship terms are regularly used.*
- It's symmetric, i.e. if A is B's the Nth cousin K times removed, then B is also A's Nth cousin K times removed. This is quite unlike most other English kinship terms, which are clearly directional: your aunt is not your niece, and your uncle is not your nephew.
- It's also gender-neutral, which also seems rather unusual compared to other common English kinship terms.
- The one thing it does seem well suited for is specifying the consanguinity or relatedness coefficient between two people, which for Nth cousins K times removed (assuming that they're not also related via other paths) equals ½ raised to the power of 1 + 2N + K (minus 1 if they're double cousins, plus 1 if they're half-cousins).
These features seem to make the degrees-and-removals system good for answering the specific question "How closely are A and B related?", but not the more general question "How is A related to B?" (for which one might resort to saying e.g. "She's the granddaughter of his aunt on the father's side" or something similar, depending on how complex the relationship chain is and which parts of it are considered most relevant). Hence my guess that this system seems to have been developed specifically for genealogy, rather than arising naturally from casual use.
But this is only a guess, and a rather vague one at that. Surely the origin of this system must be known, at least to some extent, but I'm having a hard time finding any information about it.
*) OK, I can totally see someone doing that, but only jokingly.