Re: [asa] Dawkins on the fossil record

From: John Walley <john_walley@yahoo.com>
Date: Tue Dec 15 2009 - 15:04:55 EST

I agree that this response is somewhat surprising. I thought from Dennis and several other sources, it was confirmed that we could NOT trace humanity back to a single couple like some groups like RTB say, but only to a small population.

And I think Bernie is astute to point out that the differences between any particular couple and their parents would seemingly be too minute to differentiate them specifically from their overall population. Please clear this up for us.

Also, I haven't heard from Dick on this list in a while but how could we reconcile his historical Adam theory with all humanity tracing back to a single couple amid a larger population if that was the case? Does that mean we can detect a "humanity" or an "imago dei" gene and assess who has it and who doesn't and in what concentrations? 

Due to my theological filter that has been quite exercised lately, the implications of that scenario make it very hard for me to believe that it could be true.

Thanks

John

----- Original Message ----
From: "Dehler, Bernie" <bernie.dehler@intel.com>
To: "asa@calvin.edu" <asa@calvin.edu>
Sent: Tue, December 15, 2009 2:49:00 PM
Subject: RE: [asa] Dawkins on the fossil record

David said:
" Now, if you go back far enough, you will come to a single pair that is ancestral to all modern humans."

I don't see how you could say that, as if this "single pair" didn't also have parents that were nearly identical.  What's the biological big deal between them and their parents???

...Bernie

-----Original Message-----
From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu] On Behalf Of David Campbell
Sent: Tuesday, December 15, 2009 10:26 AM
To: asa@calvin.edu
Subject: Re: [asa] Dawkins on the fossil record

Quick review on mitochondrial Eve, Y Adam, etc.:

Mitochondrial DNA is, with rare exceptions (e.g., most bivalves)
inherited entirely from the mother.  Likewise, the Y chromosome is
inherited paternally.  The rest of our DNA generally undergoes
crossing over, in which the DNA we inherit from each of our parents
gets mixed before it is transmitted to our offspring.  Thus, the
ancestry of the mitochondrial DNA and of the Y chromosome is a simple
pattern of branching and mutation.  If you come up with an estimated
mutation rate (very popular, usually statistically indefensible), you
can estimate how long ago two sequences diverged.  Other DNA, however,
gets inherited as a mosaic, and so is much trickier to trace,
especially as crossing over in various forms can take place within a
DNA region.

The most recent person to be _an_ ancestor of every living human was
estimated to be only a few thousand years ago, but I am suspicious
that the modeling did not adequately take into account geographic and
ethnic isolation.  The error bars on the estimated date for the
genetic "Adam" and "Eve" are large, but they seem not to be at the
same time.  Both would be likely to reflect a time of relatively small
population, but nothing about them indicates that they were the sole
individual of their time-just that, in the course of things, no one
else living at the time has a continuous sequence of descendants of
that same gender.  Surnames are a handy analogue.  If children always
receive their father's surname, then surnames in families that have no
sons will be lost.  If these strictly-inherited surnames never
changed, eventually everyone would have the same surname, given enough
time and random variation in whether someone has sons or daughters.
This would happen faster if the population was relatively small, or if
some males tended to have a lot more sons than did others, or if there
was some sort of pressure favoring certain names.

Now, if you go back far enough, you will come to a single pair that is
ancestral to all modern humans.  However, "far enough" is almost
certainly rather more than 100,000 years, and quite possibly at an ape
grade of evolution.  Again there is nothing to indicate that there
weren't co-existing individuals who were practically the same who
merely ended up as cousins rather than direct ancestors.

Thus, it seems that having an Adam and Eve of some sort within the
past 10,000 years or so requires them to not be the sole physical
direct ancestors of all modern humans.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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Received on Tue Dec 15 15:05:23 2009

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