[Hawthorn]

>> 10th cousin is pretty remote. <<

Yep, when we say two persons are 10th cousins, it means they share at least one GGGGGGGGGgrandparent (nine “greats”).

But when you trace that far back, you have 2048 9th-great-grandparents (if we ignore the possibility of cousin marriages).

Given this huge number of ancestors, many of whom surely have millions of descendants alive today, I think it’s likely that just about any FReeper is a 10th cousin to thousands and thousands of other FReepers — not to mention being a cousin to at least a few POTI (or POTUSES, for you people in Rio Linda).

[Verginius Rufus]

Yes, ignoring the possibility of cousin marriages (which would be common among people living in small communities--if you include marriages between second cousins or third cousins as "cousin marriages"), two 10th cousins would have two out of 2048 9th-great-grandparents in common.

In fact there is a good chance they would have only 1 9th-great-grand-parent in common, because of ancestors who were married more than once and had children by different spouses. In either case, 10th cousins may not share any DNA, unless they are descended in the direct male line from a common ancestor and share the same Y chromosome.

Normally second cousins would share 2 of 8 great-grandparents in common. In my case I have second cousins with whom I have only one great-grandparent in common, since they are descended from my grandfather's stepmother.