Re: Date for Last Common Ancestor?

Stephen Barnard (steve@megafauna.com)
Mon, 12 Aug 1996 03:56:03 -0800

Susan S. Chin wrote:
>
> Stephen Barnard (steve@megafauna.com) wrote:

> : I also have to point out (reluctantly) that you are wrong about the claim that
> : "Eve" is actually a population of more than one. We all *do* descend from a
> : single female individual, which is trivial to prove. This is precisely why the
> : "Eve" hypothesis is so devastating to the "theory of multiple and separate
> : evolutionary roots of mankind per geographic regions".
>
> : Steve Barnard
>
> Well, I know that initially when the theory of an Eve came out, that was
> the popular understanding, that we all descended from this one female.
> But tell me if I'm wrong here, but aren't we getting awfully close to
> Creationism here? If there was an "Eve," there must've been a male who
> contributed his genes towards creating that first generation of humanity
> (this sounds pretty ridiculous to me, but who am I to argue with
> science?). We therefore theoretically are also descended from that one
> male, but unfortunately his mitochondria is of no use to us. Well, it's
> getting late, so maybe it'll make more sense tomorrow.
>
> I did read about my Eve as a population and not an individual
> ancestor recently, but don't recall the source.
>
> What are you basing your one ancestral Eve idea?
>
> Susan
> --
> susansf@netcom.com

I've been called a lot of nasty things, but never before have I been
called a creationist. :-) I'm just kidding. It's a good question.

Just because "Eve" was our last *female* common ancestor, that by no
means implies that her mate was our last *male* common ancestor. In
fact, the liklihood that he was is extremely small. Since one man can
produce many more offspring than one woman, it is not unlikely that our
last male common ancestor has a much more recent date than the
mitochondrial Eve.

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