Reflectorites
On Fri, 19 May 2000 11:13:52 -0700, Cliff Lundberg wrote:
Re: The *Fact* of evolution!
>>CL>Wow, a real Darwinian. Huxley's warning against this gradualist absolutism
>>>wasn't heeded by Darwin and isn't heeded by you.
Maybe its because Darwin (and Dawkins) had read Paley's "Natural
Theology" (which I am just finishing)? They realised that *only* tiny, step-
by-step changes could hope to explain the *fantastically intricate* layers of
design that Paley documents.
Saltationists solutions are just `hand-waving'. That's why they are popular
with paleontologists who study bones, but never catch on among biologists
who are intimately aquatinted with the living *details* of life's complex
designs.
>CL>Obviously I didn't make myself very clear. Even very rapid evolution is
>>glacial compared the the span of a human lifetime. "Rapid" can mean 1000
>>years.
And it could mean only 1 year, or even 1 generation!
CL>To me the question is, what can be accomplished in one mutation,
>in one generation, one evolutionary step? Steady microevolution might
>produce geologically instantaneous large changes through Darwin's
>"insensible" gradations, but that is not proof that macromutations
>did not occur.
The problem with "macromutations" is there is no testable scientific
mechanisms to explain them. They are the naturalistic equivalent of
miracles.
CL>Plus there are serious mechanical problems in doing
>certain things gradually, as I outlined in my comments about skeletal
>elaboration, where I pointed out that articulated bones are intrinsically
>discontinuous.
Agreed. There are *huge* problems with "doing certain things gradually".
As Clark points out, most things have to pass through a functionally less
useful (or even totally useless) phase to reach the next island of
functionality. But the problem is that natural selection would weed
out anything that was less well functional:
"In order to build up a structure by natural selection, it is essential that each
stage in the building process must make an animal better fitted to its
environment than the one before it. An eye that is half developed must be
more useful to an animal than an eye that is 49 per cent developed, and this
in turn, than one, the development of which has proceeded to only 48 per
cent, and so on. The graph of usefulness against the extent of structural
organization must show a steady upward rise-otherwise progress must
inevitably stop, hindered by natural selection itself. If the graph is not a
steady upward rise, but has ups and downs, then natural selection (which
selects usefulness and adaptation), working from either direction, will force
the organism to the nearest maximum. Today, with our much greater
knowledge of and familiarity with complex systems, we know that steady
upward rises of the kind demanded by materialistic evolutionists are
unknown to science. Isolated fundamental changes make a machine less
efficient than it was before and may even make it useless, unless, indeed,
numerous other adaptations are made at the same time. The radio
manufacturer cannot turn one model of a wireless set into a larger and
better one by continuous stages-he cannot add a new valve, a condenser, a
piece of wire, etc., in a series of operations, and hope each time to obtain a
model that is slightly better than the one before. All the changes must be
made at once-or not at all! To add an extra valve to a wireless set you must
first cut through wires, disconnect the loudspeaker, etc., and at once the set
becomes useless as a functioning whole. Only after passing through the
useless stage can it be made more useful than before. It is the same with all
arrangements of matter organised as functioning units. To ask for a
gradual, uniform, improvement is, it seems, to ask for the impossible.
(Clark R.E.D., "The Universe: Plan or Accident?", 1961, pp.123-124).
In my biology class the Darwinist lecturer was obviously perplexed when
he got to the gastropod embryos which uniquely twist around 180 degrees
during development:
The most distinctive characteristic of the class Gastropoda is a process
known as torsion. During embryonic development, an asymmetrical muscle
forms, and one side of the visceral mass grows faster than the other.
Contraction of the muscle and uneven growth causes the visceral mass to
rotate up to 180 degrees, so that the anus and mantle cavity are placed
above the head in the adult (FIGURE 33.18). Some zoologists speculate
that the advantage of torsion is to place the visceral mass and heavy shell
more centrally over the snail's body." (Campbell N.A., Reece J.B. &
Mitchell L.G., "Biology," 1999, p.610)
But why would those embryos do it and not others in the Phylum
Mollusca? And if they started twisting one degree at a time for 180
degrees, they would have the worst of all worlds.
[...]
On Fri, 19 May 2000 17:21:03 EDT, Bertvan@aol.com wrote:
>CL>>>How do you explain the origin of cellular complexity, without the
>>>>macroevolutionary step of symbionts becoming genomically integrated?
>SB>>gosh, if I had the slightest idea what you are talking about I might answer
>>>that question.
The "symbionts" already had "cellular complexity". Margulis' serial
endosymbiosis theory (SET) proposes that already complex prokaryotic
cells merged with an already complex larger prokaryotic cell:
"An idea originated by the early twentieth-century Russian biologist C.
Mereschkovsky and developed extensively by Lynn Margulis of the
University of Massachusetts, the hypothesis of serial endosymbiosis
proposes that mitochondria and chloroplasts were formerly small
prokaryotes living within larger cells. (The term endosymbiont is used for
the cell that lives within another cell, termed the host cell.) The proposed
ancestors of mitochondria were aerobic heterotrophic prokaryotes that
became endosymbionts. The proposed ancestors of chloroplasts in early
eukaryotes were photosynthetic prokaryotes, probably cyanobacteria, that
became endosymbionts. Perhaps the prokaryotic ancestors of mitochondria
and chloroplasts first gained entry to the host cell as undigested prey or
internal parasites. ... By whatever means the relationships began, it is not
hard to imagine the symbiosis eventually becoming mutually beneficial. A
heterotrophic host could derive nourishment from photosynthetic
endosymbionts. And in a world that was becoming increasingly aerobic, a
cell that was itself an anaerobe would have benefited from aerobic
endosymbionts that turned the oxygen to advantage. In the process of
becoming more interdependent, the host and endosymbionts would have
become a single organism, its parts inseparable. Almost all eukaryotes,
whether heterotrophic or autotrophic; have mitochondria or genetic
remnants of these organelles. Only photosynthetic eukaryotes, however,
have chloroplasts. Thus the hypothesis of serial endosymbiosis (a sequence
of endosymbiotic events) supposes that mitochondria evolved before
chloroplasts." (Campbell N.A., Reece J.B. & Mitchell L.G., "Biology,"
1999, p.522).
Margulis' endosymbiotic theory explains how cells became *more*
complex, not how they became complex. It's like two companies merging
to form a larger, more complex company. The existing companies were
already complex in the first place. Indeed, like company mergers, the
eukaryote has less complexity in some respects (e.g. no mitochondria of its
own) than it presumably had before.
But there are major problems with SET:
First, the flagella of eukaryotes are radically different from those of
prokaryotes:
"A comprehensive theory for the origin of the eukaryotic cell must also
account for the evolution of 9 + 2 flagella and cilia, which are analogous,
not homologous, to the flagella of prokaryotes." (Campbell, 1999, p.523).
Second, the DNA molecules of prokaryotes and eukaryotes and their replication
are radically different:
"The replication of a DNA molecule begins at special sites called origins of
replication. The bacterial chromosome,
which is circular, has a single origin, a stretch of DNA having a specific
sequence of nucleotides. Proteins that initiate DNA replication recognize
this sequence and attach to the DNA, separating the two strands and
opening up a replication "bubble." Replication of DNA then proceeds in
both directions, until the entire molecule is copied. In
contrast to the bacterial chromosome, each eukaryotic chromosome has
hundreds or thousands of replication origins Multiple replication bubbles
form and eventually fuse, thus speeding up the copying of the very long
DNA molecules. As in bacteria, DNA replication
proceeds in both directions from each origin. At each end of a replication
bubble is a replication fork, a Y-shaped region where the new strands of
DNA are elongating." (Campbell, 1999, p.286).
Third, the mode of reproduction of prokaryotes (binary fission) and
eukaryotes (mitosis and meiosis) are radically different:
"Related to the evolution of the eukaryotic flagellum is the origin of mitosis
and meiosis, processes unique to eukaryotes that also employ microtubules.
Mitosis made it possible to reproduce the large genomes of the eukaryotic
nucleus, and the closely related mechanics of meiosis became an essential
process in eukaryotic sex. Among eukaryotes, sexual life cycles are the
most varied among the protists. Variety in life cycles and the diversity of
protist life in general may reflect the evolutionary "experimentation" that
occurred among the earliest eukaryotes. Let's see how systematists are
dealing with protist diversity." (Campbell, 1999, p.524).
If Margulis' endosymbiotic theory is true, it looks like it was a *very*
special series of events, that only ever happened *once* to only *one* line
of bacteria (remember it had to have happened *twice* in *one line* because
plants have both mitochondria and chloroplasts).
>CL>I was thinking of the not-so-new theory of cellular evolution through
>>the integration of free organisms into one functioning cell. I'm sure
>>you've heard of Lynn Margulis.
>
>>I'm trying to save evolutionary theory, you're making it look silly
>>by insisting on impossibilities and brushing aside objections in
>>defense of a model that was ridiculed by T.H. Huxley from the start.
I find it interesting that "evolutionary theory" is in such a parlous state that
*Cliff* has to try to "save" it!
BV>I am an ardent admirer of Margulis. She once said "Darwinism will one day be
>regarded as a quaint 20th century superstition." or something like that.
Maybe it was this:
"Margulis...wrote last December in American Zoologist, neo-Darwinism
will ultimately be viewed as only "a minor 20th-century religious sect
within the sprawling religious persuasion of Anglo-Saxon biology." (Mann
C., "Lynn Margulis: Science's Unruly Earth Mother," Science, Vol. 252, 19
April 1991, p.380)
BV>Has she written something lately? Do you know a good book or internet material
>on this "not-so-new theory of cellular evolution"?
She mentions it in her 1986 book "Microcosmos" but it is too long-winded
to quote! Probably a modern Biology ot Microbiologytext would be better.
Steve
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"Given the newcomer's ability to grow over its rival and knock it out, a
simple reading of Darwin would predict a speedy victory for the
newcomer. But in recent years, some prominent paleontologists have
questioned whether such competition among animals has all that much to
do with who wins and who loses in the evolutionary wars. High school
biology lessons notwithstanding, it's been difficult to find hard evidence
that interactions among animals matter, they noted, so externalities, such as
the meteorite that did in the dinosaurs, might be more important." (Kerr
R.A., "When Fittest Survive, Do Other Animals Matter?" Science, Vol.
288, 21 April 2000, p.414)
Stephen E. Jones | sejones@iinet.net.au | http://www.iinet.net.au/~sejones
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