Do I remember correctly that they did trace one male lineage back to a common ancestor living at the time of Moses? Jews named Cohen (or variants)?
Answered my own question. Here:
Y-chromosomal Aaron - Wikipedia
http://en.wikipedia.org/wiki/Y-chromosomal_Aaron
Neat stuff.
Ya'd think the CR/IDs would be all over this.
I believe there is a population of Jews who are descended from a common ancestor in historical times. I don't know the details, but it would not be surprising in a small population that restricts marriage outside the religion.