AncestryDNA has a very large database, second only to 23andme which is why I finally tested my own genome there in 2104, kicking and screaming the whole way.
I received my results back Easter weekend and was very pleasantly surprised to identify a known Carrow descendant, and her brother as my 4th cousin. At some point I realized I had cousins in this database who shared my Kirwan/Sweeny line.
There were other matches, not surprisingly, since I had at that point more than 11,500 matches.Eventually that amount topped out over 13,000 a ludicrous amount.A long anticipated and discussed "correction" of these matches, the majority of which were supposedly "IBS" or Identity by State was to happen late in 2014. IBD means we inherit genes from a parent and IBS essentially means they could be not ancestral at all.
This correction when it occurred left me with 11% of the matches that I had 5 minutes before. This fact is known because Ancestry saved the whole big mess from before as a download. I was able to look and see that one Kirwan cousin was my match #865 and his son #866 prior to the match. After the correction they moved up to #11 and #14 and jumped into my field of vision.
Other persons moved down in hierarchy ( if there is a hierarchy based on relatedness) and of course 89% of those matches disappeared. I sadly waved goodbye to some small Carrow matches and a few Fant from Virginia matches, who I never felt could be real anyway. My Kirwan 3rd cousin with a known ancestral ties to me moved from #24 to #57 and he tells me that I was once quite high on his list and now #27. He is still my third cousin of course but it is important to look at all changes and try to understand them.
AncestryDNA's white paper discusses ancestral "pile ups" and as an attempt to visualize them I went into Gedmatch today and posted the result of MATCHES ABOVE IN BLUE. Some of it I do see here or what I think it is because one of my Kirwan cousins is on here in an area begun and dominated by my Faunt cousin Francis. Odd as I do know that these cousins do not share my Limerick Faunts or my Donegal Dugans with me.
I am concluding at his moment that some of these segments are as a result of very very old DNA from Ireland, surely an example of "by state", in this case the SNPs are pointing to a shared ancestral region shared by many. I also realize that this is not an accurate representation of "pile ups" but since Gedmatch came up today I took a peek at the segments I was questioning.
AncestryDNA does not yet market their product in the UK so it is possible their algorithm has excluded or included certain ancestral populations or is skewed in some other fashion not yet clear to me. 23andme has begin their UK and Canadian marketing push and they will incorporate some of the "nodes" of ancestral couple in their collaboration with My Heritage which has begin it's work.