Text 1024, 178 rader
Skriven 2004-12-15 06:28:00 av Cncabej (1:278/230)
Ärende: Re: Article: Birds of a f
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W.A.>>>One word, Benjamin: Proteins.

N.C.
>>I appreciate your one-word answer. With all due respect, I don't know
>whether
>>anyone in sbe makes anything of  ":Proteins" as an answer to my question
>(How
>>genes determine bird morphology). To me it makes no more sense than other
>>one-word answers ( "God", Lipids", "Atoms", "Environment", etc.) do. No word
>>has ever been used as a substitute for a mechanism, and a mechanism is
>>exactly
>>what my question asks.  
>>
>>However, you have a chance to prove that your answer makes sense: elaborate
>>how
>> a protein or a group of proteins would provide information for the complex
>>and
>>highly specific arrangement of billions of cells of tens of different types
>>of
>>cells in the process of the development of any organ.
>>Please, illustrate with a SINGLE example (don't forget, we are fed up with
>>general unsubstantiated statements).

W.A.  
>Given the level of assertiveness implicit in your insistence that such a
>thing
>is not possible, I'm not sure how much I'm wasting my time by replying.

N.C.
I am sorry to waste your time, but don't blame me (it is your choice to). To
me, discussing with you is not a wasted time, but a real benefit.

W.A.
>Nevertheless, let me try.
>I suspect that you, like a great many other people, are under the impression
>that there is a great underlying "genetical program" ensconced somewhere in
>the
>genome of a species, not unlike the kind of program that an engineer would
>write.

N.C.
Sorry, but your suspicion is not well founded. Contrary to your opinion, I do
not belong to the class of that "great many other people"

W.A.
>But that's not true. Genes actually don't >code for much. They
>certainly
>don't code for grand designs.
>Rather, genes only encode the information on how to construct the little
>things
>of life, the pawls, cogs, screws and fasteners, each of which is a protein.
>Genes certainly don't encode wings or eyes or fingers, at least not in any
>direct sense.

N.C.
On this we generally agree. You see?

W.A.
>The machinery of life is -- perhaps astonishingly -- self-assembling. It's
>been
>that way from the very beginning, from the first bi-lipid membranous walls
>that
>formed the first cellular vessicles to the modern embryological self-assembly
>of an eye or a wing. While this answer may sound on first hearing to verge on
>the mystical, there's nothing magical all about the process.

N.C. 
First, where are your sources that "an eye or a wing" are self-assembled? Do
you have your own data? Substantiation is
absolutely necessary.
Second, help me, how on earth could proteins determine the complex and highly
specific arrangement of tens and probably hundred of different types of cells
in the developing eye or wing; no one has been able to show this.
Where is the mechanism? In the word
"selfassembly"?

W.A.
>Proteins autonomously fold into their conformational shapes based on their
>distributions of electric fields, and they lock onto one another for the very
>same reasons. But proteins are most normally not the product of just one
>gene,
>but often the result of the actions of hundreds of genes. 

N.C. 

And the source is....

>If one of the
>encoding genes is modified just a very little bit, a different amino acid may
>wind up being substituted in the ultimately realized protein, and that
>protein
>may fold in a completely different manner, making it structurally or
>catalytically more or less acceptable to the selective demands of the current
>environment.

N.C.

This is possible, but not relevant to the question on the mechanism.

W.A.
>Selection chooses only among and between the available protein variants, and
>wholly then only on the relative appropriatenesses ("fitnesses") of the
>various
>alternatives to current environmental demands. Selection does not however
>choose among and between the various underlying genes, other than in the most
>indirect manner. 

N.C.
As a statement it is correct. Selection may do all you say but this says
nothing about the mechanism.

W.A.
>As time passes, the machinery of cell inherently becomes more complex for no
>reason more complicated than the evolving phenotype is becoming increasingly
>more appropriate to the environmental demands it encounters and
>simultaneously
>more efficiently exploitive of those same environments. The most salient
>attribute of evolution is that it is a learning algorithm. But evolution is
>not
>a process that operates only through time. As phyletic lineages increasingly
>better learn their environments, they simultaneously become bound to the
>those
>environments as well. Species diversification, the evolution of complexity --
>both behaviorally and morphologically -- and the evolution of intelligence
>are
>all similar questions interwoven onto a biogeographic tapestry.

>But the one word remains: "Proteins."

N.C.
For the sake of argument I would fully agree with your statement, but you have
failed in presenting here something however distantly resembling a mechanism. 

Are you talking for selfassembling of proteins or cells? If the first, that is
not related AT ALL with the process of the development of the multicellular
morphology, with that extremely specific and complex arrangement of various
types of cells that gives rise, in our visual perception, to animal morphology.
 If the second, you have to show where proteins store the information necessary
for assembling supracellular structures and how that information is provided to
the developing structures. It would be indeed a great revelation if some day,
somewhere, someone would present  mechanism, however hypothetical, on how this
may take place. 

 W.A.
>If this explanation is insufficient -- and of course it's very short -- let
>me
>recommend the following sequence of classes at your nearest university:
>
>     one semester of organic chemistry
>     two semester of biochemistry 
>     one semester of enzyme kinetics
>     one semester of comparative anatomy
>     one semester of animal physiology
>
>By the end of this sequence, you will be able to very clearly answer the
>question of how genes (even they don't encode much, certainly not a grand
>design) "encode" the construction of a particular species of bird.
 
N.C.
Sending me back to university? First your suggestion made me laugh, but soon I
felt ashamed and now I doubt about my intellectual qualifications: with my
degree in chemistry (and a Ph.D. in biology) (which imply a little more than
your recommended sequence of classes) earned years ago, I am still far from 
being "able to very clearly answer the question of how genes "encode" the
construction of a particular species of bird".

Thank you,

Nelson R. Cabej
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