Do you think most generations have more than 30 years' age difference between mother and child? Fine, make it 1500 years. Unless you think women were still having children at age 45.
Just ONE pair of common ancestors, out of countless thousands, would result in millions of descendants by now...as the numbers more than double each generation coming back this way.
So? Explain how current inhabitants of two societies separated from each other for 1500 years are going to have any common ancestors within 33 generations (earlier I was assuming 30 years/generation, but I guess it's conceivable a society could theoretically have generations longer than that; I really doubt any society is going to have generations longer than 45 years).
Well, just going on my own genealogy - in my 33rd generation, for example - let's take Edmund (Ironside) - he was born in 989AD. (1016 years ago. You originally said 1000 years re these societies that separated.... ) No, the average generation isn't 45 yrs - but women did, routinely HAVE children at that age. They had many children back then , not unusual to have 10-12.
a paper from MIT: http://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf has some great charts near bottom
other info
http://groups.msn.com/Evolucionarios/revistadprensa.msnw?action=get_message&mview=0&ID_Message=6763&LastModified=4675494866115736780
"Roberts (Gary Boyd Roberts, noted genalogist/author) also says "anthropologists claim everyone on earth is a 40th cousin"