21 Jan 95 14:30:38 -0600

> 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
When the Magna Carta was displayed on a tour perhaps 20 years ago, they had a
list of many well known people, I think including Kennedy, who were descended
from, I think, King John. I think you are looking at less than 1000 years
ago. In a random mating population, the expected time since a common ancestor
of two individuals is about N generations where N is the population size.
However, many pairs of people will have shorter times. Also, the prominent
people throughout the ages probably form a somewhat isolated subpopulation
of the entire human population, thereby providing a shorter time since common

R. Campbell