Re: Date for Last Common Ancestor?

Stephen Barnard (
Tue, 13 Aug 1996 12:42:32 -0800

Jane Andrews wrote:
> On Mon, 12 Aug 1996, Stephen Barnard wrote:
> > Susan S. Chin wrote:
> > >
> > > I did read about my Eve as a population and not an individual
> > > ancestor recently, but don't recall the source.
> > > > >
> then stephen replied (amongst other things)
> >
> > Here's the logic that demonstrates that there is a single Last Common
> > (female) Ancestor:
> >
> > 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.
> >
> > Steve Barnard
> >
> >
> I with Susan on this one. Unfortunatly I can't remember the reference
> either (I can go and look it up tomorrow if anyone's interested) but I
> remember reading a paper which idicated that the proposed "eve" could have
> come from an ancestoral population of up to 10 000 individuals. Her
> mitochondrial sequence has been preserved by random genetic drift and all
> the others lost by chance, stochastic processes. This means that there
> is no need to invoke a huge bottle neck reducing, the effective
> female population to one, in order to explain the apparent single female
> ancestor.


> Jane Andrews.

See my later post (and a slight correction) where I flesh out this argument.
I freely admit that there *may* be a flaw in it, but I don't see it, and I'd
really like someone to point it out if it exists.

The argument seems to demonstrate that, except for a chain of circumstances
that would be vanishingly unlikely, there really is a single last common
female ancestor.

Now, whether the date of the "Eve" that was deduced from mDNA is accurate, I
don't know.

Steve Barnard