Jeff at SG
I totally agree with you. In some of my lectures many years ago I had a section with a PowerPoint slide that asked 'who in this room is descended from King David?'
I then went on to show the increasing numbers of people needed in each ancestral generation and showed just like you that it soon exceeded the number of people alive on the planet at that time (leave alone just Jews). Of course that was because the same individuals appeared repeatedly in many different places in the ancestral tree.
I also presented a study by the Yale statstician Joseph Chang (Advances in Applied Probability, 1999) who calculated that if an individual moved into a certain area of the world and had at least one child, then, 800 years later:
=E2=80=94there was a 20% chance that that individual's line had gone extinct. That is, there was no one living in that part of the world descended from him.
=E2=80=94there was an 80% chance that individual was the direct ancestor of everyone in that part of the world.
The final slide in this section then rre-asked the question of who in the room was descended from King David. With my verbal answer, 'probably everyone'.
Another interesting point related to me by Bennet Greenspan is that even though there are several families claiming direct male descent from King David (actually from his descendants, the exilarchs in Babylonia) their Y-DNAs did not match. So they couldn't possibly all be direct male descendants.....
I always though claiming Davidic descent was silly. Even though the British Royal family also makes that claim.