I don't know about alternate universes (though it's a cool theory), but apart from the Berenstein/stain thing, I've also had so-called "false memories" from time to time. I'll bring up conversations I would swear on my life I've had with someone, and they won't have a clue what I'm talking about. It has happened to other family members too; sometimes my mother will bring up a past event or conversation and the rest of the family will assure her it never happened. My sister can remember things from our childhood that none of the rest of us do, and we don't believe her until she breaks out an old diary and it's there in black and white.

Another example of the brain playing tricks: There are so, so many times I get stopped in public or at my job by a customer, someone who swears they know me from somewhere, or that I must be related to so-and-so, when there is no actual connection. Apparently I have "one of those faces" and I seem familiar to many people. One of the most interesting times that happened was when I was 18 and browsing around in the local Head shop, this girl came up and hugged me from behind. I didn't recognize her, but she started asking me when I moved to the little Georgia town we were in, or was I just there to visit her? Despite my protests, she swore I was her high school sweetheart from Oregon, right down to my accent, mannerisms, smile, eyes, and build. I had to show her my license before she could accept I wasn't him. I would have thought she had a mental disorder if not for her best friend right beside her going on and on about how I could be his twin.

I'm sure a geneticist or anthropologist could offer a theory on my uncanny resemblance to her friend in that particular instance (that, or my mother had twins and never told anyone), but it doesn't explain why so many other people see a familiar face when they look at me. Maybe I'm just that plain-faced that it's easy for others to project a known face onto mine.