Re: [asa] Two questions... (biological bottlenecking with Adam and Eve)

> It seems to me that the DNA code would change very subtly over time. I don't understand how any individual DNA change would differentiate a human from a non-human parent. It seems to me, to think otherwise, is to think as a progressive creationist. Is that the problem in accepting the idea that a first biological human is impossible- due to left-over baggage from progressive creationist thinking (they think different species were made by God by fiat at different times in history through the eons)?<

The genome can change relatively abruptly (e.g., large-scale
duplication) or gradually, and the rate of mutation is variable both
over time and in different places in the genome.

> What do you mean by "short interval?" I think in the common vernacular it means a few years, but you are meaning maybe hundreds of years and a few generations (biologically a "short time" is a very long time in the common vernacular?), correct?<

It is not absolutely impossible that a single mutation affected a
number of genes in a critical fashion related to our mental abilities,
but in general, as my grad degrees are in geology, my idea of a short
time is indeed longer than average.

> The way I see evolution is like looking at a scale from white to black, which passes through many grey-scales. If one asks "where is it black or white," it is obvious on the ends. But if you ask "where did it first turn black" no one can tell, because the change is so subtle. The same with evolution- going from apelike creature to human is like going from white to black. All the intermediates are grey-scale, so it is impossible to say there's a first black (or first human- Adam and Eve). When you and George say there is a possibility for a first biological human couple, that is saying it is possible to determine that first black from the grey-scale. That's my disagreement. Here is a picture of what I mean:
> http://www.sciencelovesreligion.com/images/grey-sc1.JPG

What I am is saying is that, if you decide for some reason that
55.68723% black is the dividing line, you can pin that down fairly
well. It's also probable that the greyscale continuum is not entirely
smooth-there would be "brief" intervals and possibly even single
individuals showing distinct changes relative to what's before.

> I think you are referring to the merging to make human chromosome #2. How could that happen? It is very unlikely (so unlikely it is impossible?) that this happened at the same time with a male and female, as if it was Adam and Eve. Therefore- there must have been some cross-breeding with merged and unmerged chromosomal creatures- correct?<

The most likely setting for it getting established would be in a very
small, inbred population (it happens in mice in isolated valleys in
the Alps). Someone anxious to have a more literal interpretation of
the text could manage things with miraculous construction of Eve from
Adam's rib. Otherwise, the most likely scenario would be for it to
arise in one individual and persist by breeding between descendants of
that individual. I don't know of any ethical way to directly
investigate the effects of the chromosome fusion in humans, but
typically the problem caused by such events is that when chromosomes
are supposed to pair up and then sort out during meiosis (production
of gametes), the mismatched ones have a hard time going to the right
places. As a result, individuals with one parent with fused
chromosome and one parent with unfused will have reduced fertility
(not counting the option of asexual reproduction in many cases of
chromosome mismatch in other organisms). A familiar example of the
same type of problem is that many seedles fruits are triploids. The
inability to properly sort out the chromosomes into pairs leads to
failed development of seeds. (The invasive freshwater Asian clam,
Corbicula, is the only more or less sexually reproducing triploid I
know of).

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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