Erland Gadde (
Fri, 20 Jan 1995 16:12:13 GMT

In article <>, (Steve Hayes) wrote:

> The number of avid genealogists is quite small, and in many societies people
> have no idea who they are related to beyond their great grandparents and
> their descendants. Even those societies that do keep track of ancestry
> usually keep track of one line only - direct patrilineal or matrilineal
> descent. So there are many fourth, fifth, sixth and seventh cousins who
> intermarry, and have no idea at all that they are related. Perhaps the
> increasing popularity of genealogy will make it possible for people to
> calculate an average of marriages to cousins at each generation.

This makes me think of a problem I have been thinking of for a long time:
Given two arbitrary persons, how far back must we go (in average) to find
a common ancestor? What if they live in the same country, the same city, etc.
I think this number is much smaller than one might think; Some ten years ago I
saw in a newspaper that someone had found a common ancestor to Queen
Elisabeth, J. F. Kennedy, Ronald Reagan, Fidel Castro, and some other
famous people. If I remember correctly, this common ancestor lived in
Ireland about 1000 years ago.

Does anybody know anything about this?

Erland Gadde