My #3 son has a wonderful girlfriend whom he's been seeing since this past spring. Recently, she sent me a photo of her mother's Uncle Jim. When her mother met my son for the first time, she was immediately struck by the incredible resemblance between these two men who were born decades apart and totally unrelated by blood.
Here is an old photo of my son's girlfriend's great-uncle:
I think it would be so strange to have a doppelganger. I can't imagine what that's like (and when the twins are older, perhaps I can find out from them exactly how it feels to see your mirror image in another person). Back on 3/18/12, I wrote a post about a friend of ours who was sure he'd seen me at Mass on a Sunday when my husband and I were most definitely out of town, but I have yet to see this woman with my own eyes. I have, however, seen the resemblance between my boy and his girlfriend's Great-Uncle Jim. And it is indeed striking.
I guess if you go back far enough, though, we're all related--aren't we?