Re: Date for Last Common Ancestor?
T&B Schmal (schmal@firstnethou.com)
Tue, 13 Aug 1996 23:18:48 +0000
In article <3210E8B8.7F5@megafauna.com>, steve@megafauna.com wrote:
> Let S_1 be the set of all people whom are alive today. Let S_2 be the
> set of mothers of the members of S_1. In general, let S_k be the set
> of mothers of S_k-1. The size of these sets is nondecreasing (S_k <=
> S_k-1), because everyone has only one mother, but some mothers have
> more than one child. When the size of the set reaches 1 then we have
> arrived at the mitochondrial Eve.
I am with you until the set reaches 1. At that point we have the LCA, who
may or may not be "mitochondrial" Eve.
Suppose mitochondrial Eve living 200 Kya owned one of fifty possibly
mitrochondria at the time. Other than that she was nothing special. Her
descendants had no particular edge over anyone else and her mtDNA remained
a small percentge of the various kinds of mtDNA in existence. But say
one day 50 Kya a human who happened to have her mtDNA was blessed with the
gift of full speech and that person's descendants quickly populated the
earth. That human would be the "speech" Eve and she would be the LCA, the
set of 1 you calculate. Mitrochondrial Eve would be way out of the
running as the LCA.
I'm not sure if Last Common Ancestor can be defined genetically, but it
certainly can be defined through lineage. My thesis is that if you can
find the LCA you can find the point that true modern man emerged. So where
(when) would be a good place to look?
Tom Schmal
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