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Archiver > GENEALOGY-DNA > 2009-12 > 1260226112


From: "Alister John Marsh" <>
Subject: Re: [DNA] R-U152 and R-L21 on the European Continent
Date: Tue, 8 Dec 2009 11:48:32 +1300
References: <59915.56775.qm@web81103.mail.mud.yahoo.com><06F79C98-398C-4200-8D9C-5BA976ABD233@vizachero.com><ea3bd9560912061730y581da805v54dec4a73733efee@mail.gmail.com><006701ca76ef$d0ab50b0$7201f210$@org><ea3bd9560912071008k310d198dre58efe3f4d2676cc@mail.gmail.com>
In-Reply-To: <ea3bd9560912071008k310d198dre58efe3f4d2676cc@mail.gmail.com>


David,

You said....

>>>>>>>
Perhaps it is necessary to turn to the chemistry of the system to understand
why it is a weak assumption to take a snapshot of what is evident from today
(e.g., via father - son observation of mutation rates), and say that it must
have been so in the past. The more I learn about the process of
methylation, and the role of histones in gene expression and other genetic
mechanisms, the more it becomes apparent that environmental factors (which
of course have not been constant over the eons) can impact on what occurs at
the genomic level. Basically, in my view, without considering epigentics
the snapshot is going to be very blurry and the interpretation of what is
seen could be out and out wrong. Mutation rates may have to consider both
time and place. Boil it down and what I am saying is that the confidence
interval of any interclade date proposed is likely so large as to afford a
very high probability of being vastly off the mark when sailing in the
waters beyond "genealogical time" (e.g., 1300 AD or so when surnames were
adopted).

Dr. Zhivotovsky has at least offered one approach that would compensate to a
degree for the above, but I would argue that using a single figure for such
a complex process may "work" some of the time and for some locations, but
surely it is not able to capture the spectrum of change from the "Dark Ages"
through the mists of early time (e.g., Paleolithic).
<<<<<<<

My views are similar to yours on this.

Recently I was rewatching a programme on plagues and mutations which
provided resistance to plagues. There was statistical evidence given that a
population hit drastically by one plague incident many hundreds of years ago
had selected certain mutations for survival above others in those
communities, and those mutations were more common today in that isolated
community than in neighbouring communities which missed that severe plague.


All or most Y-DNA mutations may seem benign in a comfortable environment,
and may be passed on for hundreds of years. But if a major stressor hits a
population, plague, famine, tsunami, volcano, war or whatever, it may place
for the first time evolutionary pressures on the survival of some mutations
which have seemed benign for hundreds or thousands of years. Using
father-son mutation rates to infer long term rates "may" be risky.

In the case of mtDNA SNP mutations, one study involving Iceland suggested
that when part of a population moved from the ancestral environment to quite
different environment, the rate of accumulation of SNP mutations differed
between the home population and the relocated population, where different
evolutionary pressures were present.

I wonder if it is possible that some seemingly benign Y-DNA STR mutations
might be either advantageous or disadvantageous in the face of "severe"
population stressors. We would not detect this effect in father son studies
in a comfortable environment.

Even social structure might affect survival of Y-DNA mutations to some
degree. In polygamist societies where a dominant male has many wives, Y-DNA
STR/ SNP mutations may be involved to some degree in selecting the alpha
male, if surviving intense competition is necessary to father the bulk of
the next generation.

In a non polygamist society, where modern medicine and science keep the weak
child alive at birth, most males survive, and have an opportunity to breed
and pass on their less favourable mutations. They may even pass on
beneficial mutations which might have been lost had they not survived at
birth with the help of modern medicine. What ever is going on is likely to
be extraordinarily complex.

Some good well dated archaeological Y-DNA would be interesting evidence to
consider.

John.




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