Stephen E. Jones wrote:
>The two-`Adam' theory is supported by the fact that Genesis 1 and 2 are
>separated by the footer "These are the generations of the heavens and of
>the earth when they were created, " (Gn 2:4a AV), since that means that
>the "man" of Genesis 1:26-27 and the "Adam" of Genesis 2:20ff were on
>two separate source tablets.
Separate source tablets suggests separate authors, which would support
the view that Genesis was a compilation of similar texts, rather than being
one author talking about two different things.
>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.
>
>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?
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.
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.
>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.
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.
I imagine that sex would be prior to the agglutination into segmented
organisms. Each segment would have its own set of gonads, possibly
hermaphroditically, as well as its own set of the other organs. 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.
>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.
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?
>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.
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.
>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.
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.
>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:
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. 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.
>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.
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.
>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.
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.
>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:
>
>"Increasing diversity and multiple transitions seem to reflect a determined
>and inexorable progression toward higher things. But the paleontological
>record supports no such interpretation. There has been no steady progress
>in the higher development of organic design. 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)
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.
>>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.
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.
>"Message theory says life was designed as a biotic message. Life was
>designed to look like the product of a single designer (the unifying
>message). Yet life was also designed to resist evolutionary interpretation
>(the non-naturalistic message)." (ReMine W.J., "The Biotic Message, 1993,
>p261)
How do you tell when something is merely difficult, and when it is actually
designed to defy scientific explanation?
>As a proponent of Progressive Mediate Creation, I have my own
>"explanation for this unacceptable irregularity in the flow of history" and
>unlike naturalistic evolutionary theories, one which *does* explain it. That
>is, I take the pattern of Genesis 1 seriously. It really does depict what
>Daniel Dennett (of all people) correctly identified as "successive waves of
>Creation:
I have to wonder why my model explaining the Cambrian evolutionary leap
would be unwelcome to one who recognizes that there was a leap. The
neo-Darwinian gradualists are the natural enemy of this model.
>Evolutionists of all stripes (including Darwinian, non-Darwinian, theistic,
>etc) all make IMHO one fundamental mistake. They assume that life's
>systems were designed to evolve. When all the evidence is that they were
>designed *not* to evolve!
There is stasis, and there is change. I don't see how to get along without
both.
>In my Mediate Creation general theory, the ultimate cause of why new
>designs appear episodically and progressively in throughout the history of
>life is because the Creator said "Let there be... and there was..." Let there
>be ... and there was..." (Gn 1:3ff).
Then, why get involved in scientific details at all? You've got the final
answer, you're all set. There's no point in learning science so you can
teach theology. When you get around to your final ID-argument, the
scientists will tune out, insofar as they are scientists.
>Unlike "the arrangement of rocks on the surface of the moon",
>which are random and unstructured, a gene (like the 200 nucleotide
>base-pair Hist4 gene which codes for Histone-4) has a precise
>"rung" structure, held in place by hydrogen bond "fixings" within a
>sugar-phosphate "ladder" backbone (correct me if I'm wrong Mike!).
>...
>Since there are only about 10^80 elementary particles in the whole
>universe, and there have only been about 10^18 seconds since the Big
>Bang 15 bya, it is vastly improbable that even *one* string of 200
>nucleotide base pairs came into existence to form a gene by chance.
This mathematical objection ignores the basic evolutionary concept
of bootstrapping, of complexity being conserved and facilitating the
accretion of further complexity. This argument demands that complex
patterns fall into place all at once, which is hardly the evolutionary
position.
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com
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