A bit of background: I have been trying to include DNA as part of my genealogical research and have tested myself, both my parents, my paternal grandmother, and my maternal grandfather on 23andMe. The ethnicity results have generally been consistent with what I expect given my documented family tree. However, there have been a couple of interesting trace ethnicities which have not been consistent. One of these traces is ~0.5% Broadly Central and South Asian in my mother's estimate.
I typically have not put much stake in these ethnicity estimates, instead focusing on matches for DNA confirmation. However, recently I was recently doing a bit of work triangulating some of my mother's matches on 23andMe and stumbled upon an interesting observation. I successfully triangulated a DNA confirmation back to my great great great grandmother Betsey Caroline (Davis) Amadon, and the segment that was used for this triangulation almost entirely consisted of the Broadly Central and South Asian segment found in the ethnicity estimate.
On paper, Betsey's ancestors are 100% English, minus some uncertainty in a few incomplete lines. The way I see it, there are a couple options:
Betsey's tree is incorrect or she has an Asian ancestor further back than what has been researched. I'm not an expert on historical demographics of New England, but it seems there was not a significant Asian population prior to the 1750's* which is the latest I would expect an Asian ancestor for Betsey to exist. As such, I think this option is relatively unlikely.
23andMe's ethnicity estimate is incorrect. My hypothesis is that given the lengthy English presence in India, some of the Broadly Central and South Asian reference population used for the ethnicity estimate had (possibly unknowingly) some English ancestry in common with Betsey. I think this is the most likely scenario.
I would appreciate any input on my findings. Does Betsey look like she might be part Central or South Asian? Is there another option that I am overlooking? Has anyone else stumbled upon a similar case? How would I proceed researching this, and is there any way to update 23andMe with this finding, especially if option #2 is correct?
*I say I believe there was no significant Asian population but I also have an anecdote which refutes this. Another hobby of mine has been metal detecting and in a pasture behind my parent's house in Vermont I found a Chinese coin dating from the late 1600's to early 1700's. I do not believe this was a later replica given other nearby finds (square nails, ox shoes, lead beads possibly for weights or counting). I am not sure if there was actually a Chinese presence at this time or if this was acquire through trade, but this does give a little more weight towards option #1.