Shocking triangulations

[Frederator]

For any match large enough to interest me, my practice is to attempt to independently draw up trees based on public sources. It's incredibly time consuming, but necessary as an occasional significant error has turned up.

But it shocks me how often my matches separately share ancestry that is not relevant to the specific MRCA I share with them. Sometimes there is even a hornet's nest of shared relationships pertaining to the same segment (e.g., Donors A and B both descend from Ancestor #1, Donors B and C descend from Ancestor # 2, Donors C and A descend from Ancestor # 3, and these ancestors lived thousands of miles apart at different times and probably weren't even from the same ethnic group, etc.). On one single DNA segment I found something like 5 of these 'non-operative' (i.e., mutually inconsistent) relationships.

Sometimes it makes me wonder how confident a person can be about conclusions. Almost everybody has significant brick walls in some recent branch or other.

[ltd-jean-pull]

Maybe their trees are wrong?

We have a match (known relationship, 4th cousin) who is descended from a couple who married in Yorkshire in 1818. There's two useful matching segments.

Most of the people who:
1) match on either of the segments
2) haves trees and/or surname lists with locations
3) reply to e-mails
....and not many have that trifecta....have Yorkshire ancestry. One had concentrated on her mother's line, and just had a name and "England" for her grandfather, so I've built a bit of a tree for him. I've found his birth in the same city my gtgt-grandmother & her male line back to the 1750s or so were from.

There's another mutual match in Canada with ancestors from England and Scotland. None are from Yorkshire. I can tell that he thinks my suggestion that there could be a Yorkshire connection is preposterous. There's certainly nothing in his paper trail to suggest it.

[Frederator]

Maybe their trees are wrong?.
. .

That's why I added the point about my independent verification procedures. These particular branches are not wrong, not unless there has been a tidal wave of unreported NPEs, which, coincidentally, only affect these particular families. Which is probably the only thing I could imagine weirder than the pattern I've already observed.

Obviously I have no way of estimating the extent of these types of coincidences in the general population, but my sense is it is higher than most people think. I doubt most people have the time or willingness to expend the level of effort I have.

[Frederator]

. . . There's another mutual match in Canada with ancestors from England and Scotland. None are from Yorkshire. I can tell that he thinks my suggestion that there could be a Yorkshire connection is preposterous. There's certainly nothing in his paper trail to suggest it.

I don't get too worked up about individual anomalous cases where at least there is some shared ancestry from the same country or a region that spans neighboring countries.

But then again I haven't had any luck at all on my single English line. The best I've had to date--and given the remoteness of my English ancestry I suppose I'm lucky to have gotten this at all--is a single segment shared by a handful of English-born people. I can say that the region generally is "North-ish", but no interesting patterns beyond that.

I know this one segment is not a reasonable basis for this opinion, but sometimes I feel as if there is somehow something "meaningless" about English DNA, as if these ancestors were not real people with individual identities, but instead just get swallowed up in this amorphous "English" identity.

My Irish matches have something of this quality. I don't even trust in my attempts to triangulate to a particular county or region within Ireland any more. But at least there the shortcomings of the documentary record and unusual demographic history (e.g., 18th century population explosion) help this make sense.

Maybe if the segment size of the anomalous match was >20 cM I might get curious. But very few are. Plus I've seen 13 cM segments turn out to be bogus.