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Archiver > GENEALOGY-DNA > 2009-07 > 1247398778


From: Vincent Vizachero <>
Subject: Re: [DNA] R1b Origins (was OurEuropeangeographicalblock. . .)
Date: Sun, 12 Jul 2009 07:39:38 -0400
References: <961517.46056.qm@web81108.mail.mud.yahoo.com><4A596878.4000108@san.rr.com>
In-Reply-To: <4A596878.4000108@san.rr.com>


Al,

Using short haplotypes does offer less resolution than longer ones,
but that's not the primary problem with Zhiv et al. in my mind.

Specifically, Zhiv et al. were not trying to do the thing we are
trying to do. That is, they were not trying to estimate TMRCA. They
were trying to estimate some other thing, which they don't really give
a name but which you or I might call a founding event or migration
event. They were attempting to use variance and extrapolate it it to
cover something other than that which it actually represents.

Imagine at some point in the past an island that is uninhabited and
always has been. Now imagine some small group of people arriving on
the island (say 40 men and women). For whatever reason - size or
resources or chance - the population of the island remains small for a
long period of time. If you visit this island 200 generations after
the arrival of these people you'd most likely observe two things.

1. An archaelogical record that would date the arrival to about 200
generations ago.

2. A genetic record that shows the TMRCA for the current inhabitants
to be something less (probably a lot less) than 200 generations ago.
Not because anything was wrong with the genetic record, but because
the TMRCA really is less than 200 generations.

Zhiv et al. were looking for a way to reconcile those two data
points. It is hard to imagine why they chose the procedure they
chose, but I can see the logic behind their decision. What I cannot
see is the logic behind taking an inelegant solution to one problem
and trying to use it to solve a completely different problem.

Zhiv rates should NEVER be used to estimate TMRCA (that's not what
they were originally derived to do) and they should NEVER be used at
all except in the cases of very small, very isolated populations
(which is the limited case in which they were derived). Using them to
estimate TMRCA for R1b1b2 in Europe violates both prohibitions.


VV

On Jul 12, 2009, at 12:37 AM, Al Aburto wrote:

> I think the fundamental problem from the very beginning is the
> geneticists assuming that a 5 or 6 or 10 Y-STR marker set gives good
> and
> accurate resolution in time.

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