Are You Related To Everyone?

This is from StraightDope.com:

"If you go back far enough, however, pedigree collapse happens to everybody. Think of your personal family tree as a diamond-shaped array imposed on the ever-spreading fan of human generations. (I told you this was cosmic.) As you trace your pedigree back, the number of ancestors in each generation increases steadily up to a point, then slows, stops, and finally collapses. Go back far enough and no doubt you would find that you and all your ancestors were descended from the first human tribe in some remote Mesopotamian village. Or, if you like, from Adam and Eve in the Garden of Eden.

"These simple facts have given rise to some remarkable displays of statistical pyrotechnics. Demographer Kenneth Wachtel estimates that the typical English child born in 1947 would have had around 60,000 theoretical ancestors at the time of the discovery of America. Of this number, 95 percent would have been different individuals and 5 percent duplicates. (Sounds like Invasion of the Body Snatchers, but you know what I mean.) Twenty generations back the kid would have 600,000 ancestors, one-third of which would be duplicates. At the time of the Black Death, he'd have had 3.5 million--30 percent real, 70 percent duplicates. The maximum number of "real" ancestors occurs around 1200 AD--2 million, some 80 percent of the population of England."

Are You Related to Yourself?