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From:
Subject: Re: [DNA] How many Ancestral lines do we have?
Date: Fri, 17 Jun 2005 13:40:56 EDT




Certainly pedigree collapse has to be considered. In the overall scheme many
lines go extinct, and catastrophic events increase the rate of extinctions.
Looking in more detail, we would also see episodes of population growth rate
increase: e.g. immigration periods in America.

I suspect that if I could look backward in time in my own lineage, I would
see episodes of growth & decline, my ancestral family size sort of
"oscillating" along it's evolutionary pathway to the present.

Mike ...
==================================================

In a message dated 6/17/2005 10:29:33 AM Pacific Standard Time,
writes:

Louis wrote:
> I was wondering how many Ancestor lines we have, since humans came into
> being?

As Ken already pointed out, the nominal number just grows exponentially.
If we assume "humans" came into being 2 million years ago and allow 20
years per generation since then, this nominal number is 10 to the
30,000th power.

> In calculating the # of total ancestors I have for this process, would I
> have to take into consideration “pedigree collapse”?

If you don't take pedigree collapse into consideration, then you're
stuck with that more-than-astronomical number. If you *do* take it
into account and look back to the dawn of humanity, then there are two
different ways to count lines. If you're interested only in Y-DNA or
mtDNA lines that start somewhere on your pedigree chart and then
continue on back, the collapse goes all the way down to one male and
one female. If, instead, you want to count autosomal ancestors (in
the mating sense, as Ken described it), then you need to pick a
reference time and figure out how many of the humans living at that
time have descendants today. It might also turn out to be two, but it
could be more. Unfortunately, we can't tell how many, and it could
vary a great deal according to the reference time you pick.

John Chandler





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