On Sun, 08 Dec 1996 21:13:32 -0600, Steve Clark wrote:
RL>Natural selection does not explain how life evolved from nothing.
SC>...However, if your comment means that natural selection does
>not provide a MODEL for evolution from nothing, then the statement
>is not entirely correct. First, the earliest steps of abiogenesis,
>or the formation of biomolecules, may not need to follow any rule
>of natural selection.
Unless blind chance is postulated, some form of "natural selection'
would be needed to bring abiotic chemicals up to the 'formation of
biomolecules":
"Even the simplest replicating macro is far from simple, however, a
composition with thousands or millions of parts, depending on how
we count the raw materials that go to make it. The alphabet letters
Adenine, Cytosine, Guanine, thymine, and Uracil are bases that are
not too complex to arise in the normal course of prebiotic affairs.
(RNA, which came before DNA, has Uracil, whereas DNA has
Thymine.) Expert opinion differs, however, on whether these blocks
could synthesize themselves by a series of coincidences into
something as fancy as a self-replicator. The chemist Graham Cairns-
Smith (1982, 1985) presents an updated version of Paley's argument,
aimed at the molecular level: The process of synthesizing DNA
fragments, even by the advanced methods of modern organic
chemists, is highly elaborate; this shows that their chance creation is
as improbable as Paley's watch in a windstorm. "Nucleotides are too
expensive" (Cairns-Smith 1985, pp.45- 49). DNA exhibits too much
design work to be a mere product of chance, Cairns-Smith argues..."
(Dennett D.C., "Darwin 's Dangerous Idea: Evolution and The
Meanings Of Life", Penguin: London UK, 1995, p157)
SC>This would only come into play with the first replicating gene
>that conferred a particular phenotype that could be acted upon by
>the environment.
Sorry, but the *bare minimum* is know thought to be a *system* of
256 genes:
"Arcady Mushegian and Eugene Koonin of the National Center for
Biotechnology Information reasoned that any genes such diverse
species hold in common are likely essential for basic cell function.
That number adds up to 240. To cover certain enzyme functions
critical for cell survival. they add 22 genes, for a total of 262,
then they trim out 6 genes that appear redundant or specific to each
bacteria's adaptation for feeding on its specific host. Their final
figure, then, for the minimum genome to support cell function and
reproduction is 256. (Mushegian A.R. & Koonin E.V. , "A Minimal
Gene Set for Cellular Life Derived by Comparison of Complete
Bacterial Genomes," Proceedings of the National Academy of Sciences
USA, volume 93, 1996, pp10268-10273). Referring to their
calculation as preliminary, Mushegian and Koonin realize they may
have overlooked some critical function(s) not covered by the 256
genes. Clearly, the bacteria do have to find and attach to suitable
hosts, and some level of genetic redundancy appears essential for
species' survival. When complete genome analysis for more species,
including humans, becomes available in a few months, a more accurate
estimate of life's minimal chemical complexity will also be
available. But in the meantime, Mushegian and Koonin's work
provides a ballpark figure for determining the magnitude of the
"spontaneous generation" problem. Anyone proposing a naturalistic
interpretation for life's origin must be able to explain how 256+
genes, plus all the other chemical components and structures for
survival and reproduction put themselves together via mindless,
purposeless, non-organic processes." (Ross H, "Simplest Bacterium
Not So Simple", Facts & Faith, Reasons To Believe: Pasadena CA,
Vol. 10, No. 4, Fourth Quarter 1996, p5)
SC>Viewing the gene as the unit of selection, then the subsequent
>evolution of living forms would conceivably follow the constraints
>of natural selection. For a critique of this, see Sterleny and
>Kitcher, J of Philosophy, July, 1988 pp339-61.
Unfortunately, there is no evidence of this. Natural selection is
only supposed to work when resources are limited. I would have
thought that it would have taken a long time (if ever) for "naked" genes
to run up against resource limitations on the early earth. Besides, when this
has actually been tested, the tendency has been to devolve, ie. to
lose complexity in favour of speed of replication:
"The DNA of an organism is not self-replicating; it is not an
independent 'replicator'. The only way in which the DNA can be
accurately and completely replicated is within the context of a
dividing cell; that is to say, it is the cell that reproduces. In a classic
experiment, Spiegelman in I967 (Spiegelman, S. "An in vitro analysis
of a replicating molecule", American Scientist 55, 1967, pp221-64)
showed what happens to a molecular replicating system in a test-tube,
without any cellular organization around it. The replicating molecules
(the nucleic acid templates) require an energy source, building-blocks
(i.e. nucleotide bases), and an enzyme to help the polymerization
process that is involved in self-copying of the templates. Then away it
goes, making more copies of the specific nucleotide sequences that
define the initial templates. But the interesting result was that these
initial templates did not stay the same; they were not accurately
copied. They got shorter and shorter until they reached the minimal
size compatible with the sequence retaining self-copying properties.
And as they got shorter, the copying process went faster. So what
happened was natural selection in a test-tube: the shorter templates
that copied themselves faster become more numerous than the
slower, while the larger ones were gradually eliminated. This looks
like Darwinian evolution in a test-tube. But the interesting result was
that this evolution went one way: towards greater simplicity. Actual
evolution tends to go towards greater complexity, species becoming
more elaborate in their structure and behaviour, though the process
can also go in reverse, towards simplicity. But DNA on its own can
go nowhere but towards greater simplicity. In order for evolution of
complexity to occur DNA has to be within a cellular context; the
whole system evolves as a reproducing unit. So the notion of an
autonomous replicator is another spot on the leopard that turns out to
be an incorrect abstraction and it fades out. Weismann's dualism as a
general biological principle is incorrect. All unicellular organisms, all
plants, and many animal species, including mammals, have no
separation of germ plasm from somatoplasm. The capacity to
reproduce is a property of the whole organism, not a special
replicating part that is distinct From the rest of the reproducing
body." (Goodwin B., "How The Leopard Changed Its Spots: The
Evolution of Complexity", Phoenix: London, 1994, pp34-35)
SC>Note, I do not say that this is known fact. Rather, I simply
>wish to point out that the theory of evolution can, in fact,
>include a model for prebiotic evolution.
Unless some sort of detailed mechanism is specified, it is vacuous.
For example, if "evolution" means simply "change through time", as
the California Science Framework defines it (Johnson P.E., "Darwin
on Trial", 1993, p145), then by definition it is true, even
tautologous.
RL>Neither does it explain how mutation could explain evolution
>upward to higher more intelligent life.
SC>I don't know why you say this because this is precisely what the
>neoDarwinian synthesis explains.
Not really. The evidence is that "mutation" at best merely
"explains" "evolution" *sideways* (ie. microevolution), not
"upward" (ie. macroevolution). If Steve disputes this, please give
us *one* example of a "mutation" leading "upward to higher more
intelligent life".
BTW arch-Darwinist Dennett admits that the AIDS virus has undergone
more mutation in the last decade than the entire history of
primate evolution:
"The AIDS virus has undergone so much mutation in the last decade
that its history over that period exhibits more genetic diversity-
measured in codon revisions than is to be found in the entire history
of primate evolution! " (Dennett D.C., "Darwin 's Dangerous Idea:
Evolution and The Meanings of Life", Penguin: London UK, 1995,
p195)
Yet, despite this, it is still the AIDS virus!
[...]
RL>"what else is there besides pure chance and how can these
>something elses be creative".
SC>Natural selection is there besides chance. Chance means that any
>event has a the same probability of success as any other event.
>Natural selection says that only certain events can be successful
>in a given environment. This is the opposite of chance.
I agreed about *selection* being "the opposite of chance". But I
disagree that it should be called "natural *selection*", except
metaphorically. Nature doesn't really "select". Only intelligent
designers select. All there is is differential survival: those
individuals who survive pass on their genes to the next generation;
those who don't survive don't pass on their genes to the next
generation. Darwinism needs to dress this up in metaphorical (ie.
mythical) language to make it sound like it is the work of a
intelligent designer:
"'Natural selection'...has become not just biology's unifying
principle, but its mantra: a phrase embodying a kind of spiritual
power. Darwin himself endowed it with an almost metaphysical
quality:
'Natural selection is daily and hourly scrutinizing...every
variation, even the slightest; rejecting that which is bad,
preserving and adding up all that is good; silently and insensibly
working...at the improvement of each organic being.'
Ernst Mayr compared it to a sculptor, Gavin de Beer called it a
master of ceremonies, George Simpson thought it like a poet or a
builder, Theodosius Dobzhansky said it was similar to 'a human
activity such as performing or composing music'. But is the phrase,
at heart, empty? Is it anything more than a statement of the
obvious? Survivors survive. It seems to have been the geneticist T.
H. Morgan, pioneer of fruit fly research, who first spotted the
problem. He wrote early in this century: 'For it may be little
more than a truism to state that the individuals that are best
adapted to survive have a better chance of surviving than those not
so well adapted to survive.'" (Hitching F., "The Neck of the
Giraffe: Where Darwin Went Wrong", Ticknor & Fields: New York,
1982, p104)
RL>And where else but God does creation come from?
SC>Most of us here would agree wholeheartedly with this point.
Good. We agree on that at least! :-)
Happy New Year!
Steve
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