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Archiver > GENEALOGY-DNA > 2002-09 > 1031092980


From: "John F. Chandler" <>
Subject: Re: [DNA] Two Paleolithic Y groups in Europe Before the Third/Neolithic
Date: Tue, 3 Sep 2002 18:43 EDT
In-Reply-To: philr@stanford.edu message <5.1.0.14.2.20020903150206.01acac90@philr.pobox.stanford.edu> of Tue, 3 Sep 2002 16:02:24 -0600


Phil wrote:
> That makes it much clearer. I presume the 60,000 is subject to change as we
> expand the number of samples, but might approximate the time of the
> y-chromosome Adam. Now Annie's original question makes more sense, but
> rephrased as: why did all but one of the male patrilineal lines die out
> between 60,000 years ago and the present, while several female matilineal
> lines survive from 170,000 years ago down to the present? I presume the
> answer is mainly chance,

No, this is a global parameter, and it should be "smoothed out" so that
it says something fundamental about the human condition. Unfortunately,
it's not entirely clear what it says. For one thing, these figures have
both been scaled separately to the presumed underlying mutation rates.
A factor of two error would not be a big shock for the Y STR rate, and
I imagine the calibration of the mtDNA rate is also a bit flexible.

> although perhaps greater males mortality might
> have been a factor--such as in tribal warfare

Note that the diversity age represents an average disaster rate over
the milennia. Yes, tribal warfare plays a part, but it doesn't require
an assumption of selective killing of conquered populations by sex --
the soldiers/warriers naturally have a much higher mortality rate than
non-combatants.

> for Annie's question about those who crossed the Red Sea 80,000 years ago
> (has this hypothesis generally been accepted?), there might have been 2, 3
> or two dozen distinct y-chromosome lines that made the crossing,

That's not the way to think about it. In the same sense, there was only
one Y-DNA lineage at that time, and, just for argument's sake, let's
suppose it was then consistent with roughly the same diversity age that
we see nowadays. There would certainly have been an unending stream
of disasters in the preceding eons, so why should the diversity age
have been different? What happens in a disaster is this: the rare
haplotypes are at risk of dying out completely, while the common ones
survive. As a rule, the haplotypes that have mutated the most from
the ancestral type are the rarest. This is why the term "distinct"
lineage is a slippery one. In 60,000 years, the descendants of any
lineage will evolve in all directions, including (for example) from
hg1 modal haplotype toward hg2 modal haplotype and vice versa. Thus,
when we say that the current level of diversity is CONSISTENT WITH a
run of mutations for 60,000 years from a single individual, this does
not actually imply that all lines today descend from that hypothetical
"Y Adam" -- only that they appear to have done so.

John Chandler

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