A Segmentology TIDBIT
My Ancestor 14M was John William CAMPBELL, born 1856 NY; died 1916 WV. His parents were Samuel CAMPBELL and Ann CLARK who were married 1851 in Scotland and immigrated to the US in 1853. This 1/8 of my ancestry is the only known part to come from Scotland. Several cousins have done Y-DNA testing and the CAMPELL line is the Argyll CAMPBELLs.
I have over 125,000 Matches at AncestryDNA. I have identified Common Ancestors with over 4,500 Matches – only 5 of them are on my CAMPBELL line. About 12.5% of my DNA is from my CAMPBELL line, and, all other things being equal, about 12.5% of my Matches should come from my CAMPBELL line. But all things are not equal – this CAMPBELL line is relatively small, and there are no known Ancestors before 1850, and there are no known links to any Ancestors in Scotland.
This doesn’t mean that none of my other Matches are cousins from this CAMPBELL line. However, it does result in me not being able to find any more links. I have tens of thousands of Matches with no Trees; I’ve even found some with a CAMPBELL surname – but no way to determine if I am related to them (other than the few who have matching Y-DNA at FamilyTreeDNA).
So, I drop back and relook at the big picture: exactly 1/8 of my Ancestry came from Scotland (well, maybe not going way back, but probably within a genealogy timeframe); roughly 1/8 of my DNA came from/through Scotland; and if not 1/8, perhaps 10,000 of my Matches should be on this part of my Ancestry– certainly more than the five close cousins I already knew about.
I decided to turn this lemon into lemonade. The lemon is recent Scottish immigrant ancestor – the lemonade is Scotland ethnicity. If this is the only part of ancestry from Scotland, maybe I could use that information. When I Cluster my AncestryDNA Matches at the 20cM Threshold (the lowest cM amount with Shared Matches to each other) I get about 160 Clusters. 1/8 of those is 20 Clusters – a manageable number. So when I see some solid looking Clusters without any hints of other ancestry, maybe they are from my Scotland line.
Here is one such Cluster. I clicked on the link for each Match and checked their ethnicity:
Every Match in this Cluster has 14% to 62% Scotland ethnicity. A few scattered Matches with Scotland ethnicity might be expected randomly, but for all of them to have significant amounts of Scotland ethnicity is a strong clue.
I think I can safely assume this CL149/14/[Scotland…] Cluster represents my Ancestor, John CAMPBELL – Ahnentafel 14M. If I knew the DNA segment, I could Paint this Cluster. I have several others that also show a pretty clear Cluster “picture”. Next I’ll be looking a some other Clusters which may even have a ThruLines Common Ancestor in them, but also have a lot of Scotland ethnicity – the ThruLines CA may be the outlier… With only one ThruLines CA I don’t have a high confidence that it’s right. But with high concordance of Scottish ethnicity, that’s a strong clue the Cluster is on my CAMPBELL line.
The next step is studying any Trees in these Scotland Clusters to see if those Matches have some Common Ancestors among themselves… That will be the sweetest lemonade of all.
[22AU] Segment-ology: Using Ethnicity to Identify a Cluster TIDBIT by Jim Bartlett 20200612