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Archiver > ALT-GENEALOGY > 1999-07 > 0930895095


From: Silver Bullet< >
Subject: Re: How many ancestors are possible?
Date: Fri, 02 Jul 1999 05:58:15 GMT


In the recent past, Steven Mix wrote:

>I do differ with your above statement, though, because
>the numbers I ran did not show a percentage in the
>single whole number digits until the 19th generation.
>At the 10th, it's still a very small fractional probability
>in England. 1,024 potential ancestors out of a total
>population of several million. That's only 0.03%, not
>3.0%.

No, No No... it's the number of descendants living at a point in time
compared to the population that more reasonably determines the odds of
meeting someone with a common ancestor, not the number of ancestors in
a prior time.

If the living descendants of a SINGLE New England ancestral immigrant
couple in America today are 2,000,000, that's .7% of the total
population (270,000,000 I believe someone said).

If the total number of descendants of a New England ancestral couple
today are 4,000,000; then that's a 1.4% ratio.

The odds for ONE person of the population at random being in that
select group ranges from .7% to 1.5%.

The odds for ANY TWO people, both at random, being in that group, if I
remember my college stat class correctly, are half of that, or .375%
to .75 percent.

I don't recall how statistics would deal with the odds of two people,
selected at random, from the population, one being male and one being
female, belonging in that select group.

Two English people descended from that couple will have even greater
odds of meeting a descendant from that SINGLE couple because of the
lesser population of Britain. It will be probably be a somewhat
different ratio than just the total population ratio, (five to one, I
believe someone said), because the American descendants will have
likely dispersed and the English descendants clustered (ie the English
more likely to have some cousin duplicates in the tree, thus less
total descendants "in body count", even though the number of "boxes"
on the tree might be the same.)

Note, my estimate in number of descendants is less than from my
earlier post based on a more detailed model shown below.

______________

An American (today) will usually have not more than 100-200 New
England immigrants out of those 1,024 you mention to consider as being
descended from, whereas ALL 1,024 of an Englander will likely be
English (yes, I know, disregarding that there were English
immigrants).

What that issue has to do with is the increased odds that two English
people might be BOTH descended from MORE THAN ONE ancestral couple.
Which is a whole different issue.

Since each person of the English couple has 1,024 English forebears at
the 10th generation back, there is a much greater chance that they are
cousins to each other through MORE THAN ONE ancestor than Americans at
the tenth generation.

If you have to deal with the ancestors back in time, consider
comparing 200 possible ancestors for an American versus 1,024 for the
Englishmen. Because that's about all of the possible ancestors an
America will have in America in the 10th generation. You can't guage a
denominator for the American using this form of estimation because the
other pieces of his/her ancestral table are spread all over the globe.

______________

On the number of descendants issue. I have a 1980 genealogy of a 1760
immigrant that has 5,877 descendants (of blood, not counting spouses).
That genealogy was not complete, as it ran into a dead-end in one
major branch off the bat in the first generation, then, of course, a
number of dead-ends after that. Due to this incompleteness, and births
1980-2000, that number could easily, very easily, be well over 10,000
descendants by now.

I have selected at random, New England ancestors in my database with
the following count of blood descendants, not relatives, certainly not
complete in any case, born by 1760, of: 352, 427, 594, 772.

That would project, at 10,000 descendants for each, to a range of from
3,520,000 to 7,772,000 descendants as of today. Let's increase these
figures to 5,000,000 and 10,000,000 because these are very incomplete.
(ie presuming each New Englander had 500-1,000 descendants born before
1760.)

Let's then apply two discounts, completely unscientific in amount:
assume 40% are not living and 20% are descended from cousin marriages.
Taking away 60% from those numbers gives 2,000,000 to 4,000,000
descendants living today (some with more than one line of descent.)

This means the chances of any two Americans at random (sex
disregarded) being descendants of that ONE American New England
immigrant couple, in the year 2000, may possibly be somewhere in the
neighborhood of HALF of .7% to 1.5%, or just say 1 in about 200.

The English probability is much higher because:

1) Virtually all of the 10th generation ancestors of the English
ancestor left cousins and siblings in England who generated progeny as
candidates for cousinhood. Most American 10th Generation ancestors, if
folks even have them, came alone.

2)The smaller population of England leaves a much higher "possibility"
of connection.

3) The "clustering" in England vs "dispersion" in America.

_____________

Norris

EMail: Norris Taylor <>
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