How Far Back

[blejerh]

My mother has a shared segment of 37.4 cM on Chr. 10 with a stranger. I assumed that he would be 5th to 7th cousin or closer since I have a sixth cousin who has a 31 cM overlap with me and that's from a small village with a lot of intermarriage.

When we compared trees I found that my mother's 8th great grandmother and his nth great grandfather are siblings. That seems rather far back.

Should I look at more recent ancestors on both sides or is it possible that shared ancestor of one of my mother's 9th great grandparents (she's 87) could account for this amount of overlap?

This is early New England not Ashkenazi.

[S9 H9]

You can have quite distant cousins sharing autosomal DNA segments.

Having said that, it is of course possible these two people have a more recent common ancestor too. It is not unusual for colonials with early American ancestors to be multiple cousins.

[PDHOTLEN]

One of my most recent FF matches is from North Carolina. It barely qualifies as strong enough to be included. It points to being a relative of my 5th-level grandparents, they being born around 1757-1760. Relatives earlier than the 18th century would have to be traced via paper/online trails. I put together a plausible online-mythological direct maternal train going back to King John of England, born about 1166, and even earlier. The further back, the more likely for errors.