Reflectorites
[continued]
On Sun, 20 Feb 2000 17:33:16 -0800, Cliff Lundberg wrote:
[...]
>>CL>Nope, not in our era, that is, since the Cambrian explosion. This was a
>>>mechanism that could only produce viable organisms in a strange benign
>>>ecosystem without well-formed segmented competitors.
>SJ>Does Cliff mean "This was" the only "mechanism..."? If so, he would need
>>to substantiate that. What evidence is there that: 1) parabiosis can *even*
>>"produce viable organisms"; and 2) that it is the *only* mechanism that
>>could produce viable organisms before the Cambrian Explosion?
CL>1) I base my thinking on the fact that the panoply of arthropods and
>vertebrates appeared suddenly in the geological record, and on the
>fact that subsequent evolution in the gross morphology of these phyla
>seems to be a matter of loss and distortion of segments. This implies
>that a mechanism for drastic evolutionary multiplication of segments
>was in operation and was what kicked off the Cambrian Explosion.
>I theorize that parabiosis was the mechanism for this polymerization.
Whenever I see the question-begging habit of evolutionists sticking the
unnecessary word "evolutionary" in front of something, e.g. "drastic
evolutionary multiplication of segments" I regard it as a sign there is
something weak about the argument or evidence, or both.
That there may have been "a drastic ...multiplication of segments" may be
true. That it was "evolutionary" is one of the point in question.
That Cliff does not seem to address the question: "What evidence is there
that...parabiosis can *even* "produce viable organisms", may be because
there is something weak about the argument?
CL>2) I would never say 'only' or 'never' about the action of a particular
>biological mechanism. But we do need a mechanism for the sudden
>generation of all these segmented organisms. This is the best I can
>think of.
OK. I appreciate the amount of thought that Cliff has put into this on his
website. It is truly *awesome*. But Cliff needs to do more that just *think
of* "a mechanism for the sudden generation of all these segmented
organisms". He needs to show: 1) that it is a *viable* mechanism, i.e. it
*could* have happened; and 2) that it fits all the known facts, i.e. it *did*
happen.
>SJ>Sorry, but it is mere question-begging to say that there is "no particular
>>reason why a predisposition to Siamese-twinning should not be heritable".
>>Is there any *positive* evidence that it is heritable? And how would it
>>work in a sexual species? Somehow the two Siamese-twinned phenotypes
>>arising from one genotype has to be encoded in the genotype of one of the
>>twins.
CL>Siamese-twinning is a simple thing; it is the failure of multiple embryos to
>differentiate normally. Any sort of monkey wrench in the works could cause
>this truncation of developmental process. As to positive evidence, I suppose
>there might be drosophila mutations for this phenomenon, but that would prove
>nothing about pre-Cambrian evolution.
Siamese twins are not "the failure of multiple embryos to differentiate
normally" but *one* embryo which differentiates at an early stage, but not
completely:
"If the separation of the embryo were to come between the formation of
the chorion on day 5 and the amnion on day 9, then the resulting embryos
should have one chorion and two amnions (Figure 5.31B). This happens in
about two-thirds of human identical twins. A small percentage of identical
twins are born within a single chorion and amnion (Figure 5.31C). This
means that the division of the embryo came after day 9. Such newborns are
at risk of being conjoined ('Siamese") twins." (Gilbert S.F., "Developmental
Biology", 1994, p184).
CL>I imagine that sex would be prior to the agglutination into segmented
>organisms.
Cliff needs to clarify this vague point. It is not enough just to imagine
something. He needs to show (even in outline) how Siamese-twinning is
heritable, so that a Siamese twin thereafter produces Siamese twin
offspring.
Cliff needs to show how in his hypothetical pre-Cambrian archetype, a
Siamese twin thereafter had Siamese twin offspring.
CL>Each segment would have its own set of gonads, possibly
>hermaphroditically, as well as its own set of the other organs.
Cliff needs to clarify this, and explain how these gonads would, in a
Siamese twin, start producing Siamese twin offspring.
CL>Evolution then
>would tend toward specialization of segments, with one or a few segments'
>vital organs eventually serving the whole body; thus the formation of
>paired organs, lobed organs, multiple-chambered hearts and such.
That once this was encoded in the genome, it would reproduce itself,
providing it was viable and not selectively disadvantageous, there is no
argument.
The problem is explaining how a phenotypic change can get into the
genotype.
And since Siamese-twinning is a non-inheritable *development* disorder,
there may be no place in the genome for it to be encoded.
>SJ>In sexual reproducing species, the sex cells are just ordinary cells of one
>>phenotype, located within the gonads or ovaries, and in the case of the
>>female they divide early in the embryo's development while it is still in the
>>womb or egg. Cliff needs to explain detail how this could happen for his
>>parabiosis theory to be viable.
SJ>It's just another mutation, no matter which sex it arises in originally. Do
>I have to explain how a mutation could be favorable and be selected for?
Maybe. But first Cliff needs to explain (even in outline) how the parent's
Siamese twin development disorder, which may not be encoded in the parent's
genome, gets passed on to the offspring so that they too have Siamese-twin
offspring.
>SJ>There is as yet AFAIK no positive evidence for "a brief formative period
>>that kicks off the Cambrian". There are some trace fossils which are
>>disputed and of course there are fossils of prokaryotes and eukaryotes.
CL>Right, and then suddenly there is a multitude of new segmented organisms,
>comprising a whole new ecosystem. If one is an evolutionist, one must
>posit a formative process qualitatively different from gradualism; others
>may see this as a case of divine intervention.
Agreed! The problem for Darwinists is that no matter what the solution, it
doesn't look like it will be Darwinian. That makes Darwinism not a general
theory since it cannot explain one of the most important events of life's
history.
A fairly recent major SCIENCE issue on Evolution confirmed that
scientists still have no naturalistic explanation of the Cambrian Explosion:
"Understanding both the onset and the termination of such bursts is a major
challenge. Critical tests for the trigger or damper of the Cambrian
explosion have been difficult. Potential mechanisms are plentiful and fall
roughly into an extrinsic set of ecological or physical triggers and brakes
(10) and an intrinsic set of thresholds in the increasing complexity and later
stabilization of developmental systems. However, without a time machine
to perform reciprocal transplant experiments between Cambrian and
modern seas, the rival hypotheses so far have resisted falsification..."
(Jablonski D., "The Future of the Fossil Record", Science, vol 284, 25 June
1999, p2114).
>SJ>Some Precambrian fossils known as Ediacaran fauna have been found in
>>the immediately prior Vendian but AFAIK they are not regarded as
>>ancestral to the Cambrian phyla.
CL>Underscoring the point that the Cambrian biota were formed in a
>revolutionary phase of evolution. There is symmetry and segmentation
>of a sort in the Vendian organisms. I presume this too to be the result
>of parabiosis. But Cambrian evolution involved calcareous organisms;
>this made it special, as it involved protective casings for complex
>physiological systems; segmentation made organisms like suits of
>armor, combining hardness with flexibility.
There's that `e' word again! That it was "revolutionary" is agreed.
That it was "evolution" is the major point at issue.
But before Cliff claims it was "the result of parabiosis" he needs
to explain how Siamese-twinning can become heritable. Since parabiosis
is a devlopmental disorder, it may not even be encoded in the genome.
>SJ>Also, now exceptionally well-preserved fossils of two different species of
>>fully developed non-segmented vertebrate fish have been found in the Early
>>just after the Cambrian Explosion:
CL>I wonder how a non-segmented organism can be identified as a vertebrate.
>But the process of reduction could have been drastic early on in the Cambrian,
>in some lineages, producing amphioxus-like creatures.
Cliff would need to explain why and produce some evidence that is
*testable*.
CL>These of course will
>be seized upon as precursors, by those who favor a simple-to-complex model
>of gradual elaborative evolution. These may well have been the first vertebrates
>to radiate widely and leave fossil evidence, while lineages with more complex
>skeletons (such as gnathostomes) took longer to evolve into broad-ranging
>successful forms. These fossil finds do not prove that there was a process of
>gradual elaboration. The evidence for gradual reduction in segmented organisms
>is relatively overwhelming.
Cliff needs to state what that "overwhelming" "evidence for gradual reduction"
is and how it applies to Precambrian *vertebrate* ancestors.
>SJ>The problem is that polyploidy works (albeit only limited) because
>>genotypic changes produce phenotypic changes. There is AFAIK no
>>evidence that phenotypic changes produce permanent inheritable genotypic
>>changes. That is Lamarckism.
CL>I don't know why my suggestion about mutations producing Siamese-twinning
>should be interpreted as meaning phenotypes produce genotype changes,
>except in the Darwinian sense that natural selection bears upon the phenotype,
>which affects the 'success' of the genotype that produces the phenotype.
Then Cliff needs to explain how the genotype changes produce developmental
phenotype changes, namely Siamese twinning. Especially when there is no evidence
AFAIK that Siamese twinning is inheritable.
>SJ>That there are mechanisms for "generating...segments" is undisputed. That
>>parabiosis, ie. Siamese-twinning, is one of those mechanisms, may perhaps
>>be granted for segmented organisms like arthropods, subject to a
>>satisfactory explanation of how it would work at the genotypic level, That
>>parabiosis is *the* "mechanism for generating trains of segments" in all the
>>100 or so phyla which made up the Cambrian Explosion would require a
>>*lot* of evidence.
CL>It's a theory. Theories about the early Cambrian aren't going to be supported
>by a lot of evidence. This theory is the simplest. It'll be much harder to show
>that new segments are added through a process of gradual elaboration. The
>reduction and specialization of serial homologs is an established pattern,
>a fact of nature.
Cliff has yet to show that his parabiosis theory even works at all. He needs
to take us, step-by-step, showing how a Siamese-twinning developmental
disorder can get into the genotype of the Siamese twin's offspring, so it
becomes inheritable in the ordinary way.
>SJ>Third, even if "Darwinian gradualism" or Cliff's parabiosis theory, was
>>found to be true, it still would not explain "why eukaryotes originated ~ 1.2
>>bya and then nothing much happened for nearly 600 mya, and then in ~ 5
>>million years between ~ 575 and ~570 mya, *everything* happened". IOW,
>>it would not explain what caused the cause, i.e. what was the *ultimate*
>>cause of these chain of events. IMHO no purely naturalistic theory can
>>explain why eukaryotes did nothing for ~ 600 myr and then to suddenly
>>explode in the event known as the Cambrian Explosion. This is Gould's
>>point against Darwinian gradualism, but which Gould himself has no
>>answer:... We have had, instead, vast stretches of little or no change
>>and one evolutionary burst that created the entire system." (Gould S.J.,
"Ever Since Darwin", 1991, p118)
CL>You seems to be protesting the irregularity of history. Why should
>history have to be smooth and gradual? Eukaryotes appeared suddenly
>and so did the Cambrian fauna. The evidence implies that these organisms
>did not form gradually. The challenge for science is to discover what
>happened and to explain how it happened.
It is not just not "smooth and gradual". There are *enormous* tracts of
time when nothing happens. For example, if the 4.6 billion year history of
Earth is expressed as a year, then Prokaryotes, which appeared in the fossil
record about 3.8 bya would be on 5th March. Then Eukaryotes, which
appear about 1.7 bya would be on 19th August, a gap of 5 1/2 `months', or
nearly half the Earth's history. Then if complex animal phyla first appeared
in the Cambrian Explosion about 550 mya that would be on 18th
November, another 3 `months' or a quarter of the Earth's history. This
graph might make it clearer:
aaaa
eeeeeeeeeeeeeeeeeeeee
pppppppppppppppppppppppppppppppppppppppppppppppppppppp
J.....F.....M.....A.....M.....J.....J.....A.....S.....O.....N.....D
4.6 3.8 1.7 .55
Darwinism, and indeed any naturalistic theory of evolution needs to explain
this enormous *stasis*, which ID and Mediate and Progressive Creationist
theories can easily explain.
>SJ>I will predict that there never will be a satisfactory fully naturalistic
>>theory which can explain life's episodically progressive pattern, of which the
>>Cambrian Explosion is the most spectacular example.
CL>Why does the episodic pattern require special explanation, while
>presumably a smooth gradual pattern of change would not? I would think
>a mechanism that involves random events in an irregular landscape would
>naturally produce an episodic pattern; it may take a gradual process to
>reach a new plateau of adaptation, but once reached, radiation into the
>new plateau could be explosive.
These are IMHO just hand-waving *words*. Gaps of this magnitude: 3.8 -
1.7 = 2.1 bya between prokaryotes and eukaryotes and 1.7 -0.55 = 1.15
bya between eukaryotes and the animal phyla is not just an "episodic
pattern". If evolution is supposed to be the result of random mutations and
environmental change then why didn't it happen in those 2.1 and 1.15
*billion* years? If Siamese twinning was what caused the Cambrian
Explosion, then: 1. why didn't it happen earlier? 2. why did it happen when
it did? and 3. why did it then happen all at the same time in 50+ phyla?
[...]
[continued]
Steve
--------------------------------------------------------------------
"But although the logic seems inescapable, the importance of identifying
the concept of relationship through descent from common ancestors as
hypothesis is immediately obvious once one makes a statement like: "fish
gave rise to amphibians." How can one show that such a statement is
correct or false, which is a scientifically reasonable thing to want to do?
Although "finding ancestors" is the traditional paleontologists' "proof,"
such "historical events" cannot be tested by assembling nice series of fossils
without discontinuities, because the evolutionary hypothesis is superficially
so powerful that any reasonably graded series of forms can be thought to
have legitimacy. In fact, there is circularity in the approach that first
assumes some sort of evolutionary relatedness and then assembles a pattern
of relations from which to argue that relatedness must be true. This
interplay of data and interpretation is the Achilles' heel of the second
meaning of evolution [organisms are related by descent through common
ancestry]." (Thomson K.S., "The Meanings of Evolution", American
Scientist, Vol. 70, September-October 1982, 529-531, 529-530)
Stephen E. Jones | sejones@iinet.net.au | http://www.iinet.net.au/~sejones
--------------------------------------------------------------------
This archive was generated by hypermail 2b29 : Wed Feb 23 2000 - 16:34:42 EST