Where does the English system of kinship terms for cousins ("Nth cousin K times removed") come from?

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.}

Solution 1:

The degrees of relationship have been around for thousands of years. The more formalised system is somewhat more modern in its terms, but not in its philosophy:

OED:

Removed (adj.) a. Distant in relationship by a certain number of degrees of descent. Now esp. with reference to cousins. Cf. once removed at once adv. 7.In later use also with reference to more general designations of distant relationship, as cousin seven times removed.

The earliest reference recorded is from the early 16th century and concerns Ecclesiastical (and later Common and Criminal) law:

1502 tr. Ordynarye of Crysten Men (de Worde) iv. xiii. sig. v.v The broder and syster make ye fyrst [degree], the chyldern ye whiche ben germayns make the seconde. The chylder of these germayns the whiche ben called remoued maketh the thyrde.

[Brothers and sisters comprise the first [degree], the children that they produce comprise the second . The children of these offspring who are know as removed, make the third.]

The legal aspect was very important as it controlled who could marry whom and thus how property could be kept within a family.

The idea of “first cousin twice removed” was never intended to be a colloquial description, (for the most, “cousin” was good enough). It was, as you have pointed out:

thus good for formal documents

And there is nothing more formal than the law, and there is nothing more important than property.

All the above is based upon The Bible. From the Wikipedia article Incest in the Bible:

Incest in the Bible refers to sexual relations between certain close kinship relationships which are prohibited by the Hebrew Bible. These prohibitions are found predominantly in Leviticus 18:8–18 and 20:11–21, but also in Deuteronomy. Jewish views on incest are based on the biblical categories of forbidden relationships and have been subject to rabbinic interpretations in the Talmud.

So, in answer to your question:

where it comes from or why it works the way it does.

The answer is that someone said that God said it and someone else wrote it down. By the 16th century, (and probably somewhat earlier, the Church courts were giving judgement and had codified Leviticus, etc. into a stable form using the terms "Second cousin twice removed", etc.