Archiver > GENEALOGY-DNA > 2011-10 > 1319037546

From: "Kenneth Nordtvedt" <>
Subject: [DNA] Fw: TMRCA Calculations
Date: Wed, 19 Oct 2011 09:19:06 -0600

-----Original Message-----
From: Mike W

I recognize the true MRCA founder is "unknowable," but it appears that
practically speaking, it is the coalescence age that is important anyway. It
represents the timeframe of significant expansion, to the point where a
certain level of geographic or cultural diversity is reached and survival
probability is enhanced.

Is that a fair understanding of how one could use coalescence ages? Is there
a better way to apply of them?

-----Original Message-----
From: Kenneth Nordtvedt

Coalescence age is qualitatively in words what you describe.

[[I forgot to add that while coalescence age estimate must always be less
than the tmrca estimates, if the tree expands very fast in its early era,
the gap between tmrca and coalescence age gets smaller.

In ancient tree there are coalescence ages which can be evaluated but which
have nothing to do with the "significant expansion" you mention, however.
This happens when a population would consist of two separate populations
with their own coalescence ages, and then long branch lines back to common
node. The mathematical coalescence age in this case would be average of the
ancient common node age and coalescence ages of the separate populations.
This average could be hanging out there in the middle when absolutely
nothing has happened other than two sons carrying the batoons on from their
fathers. Such situations are, however, prime opportunities to apply the
interclade variance. ]]

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