In article <71hqv9$kco at ux.cs.niu.edu>,
rickert at cs.niu.edu (Neil Rickert) wrote:
(note-comp.ai.philosophy deleted)
>flefever at ix.netcom.com(F. Frank LeFever) writes:
> >In <71cqlh$gol at ux.cs.niu.edu> rickert at cs.niu.edu (Neil Rickert) writes:
>> >>The DNA does not construct either the pancreas or the brain. DNA is
> >>a set of specifications for making proteins. A blueprint does not
> >>construct a house or anything else, but carpenters and bricklayers
> >>may use the blueprint in carrying out their construction. DNA
> >>doesn't construct anything. The machinery of the living cell
> >>constructs, and uses the DNA in the construction.
>> >I suspect that Ray understands what you are TRYING to say, better than
> >you do yourself. Certainly, I do.
>> No, Scanlon does not understand, as his sarcastic response
> indicated.
>> However we all know that LeFever understands. After all, he is a
> world expert, as he has been so clear to tell us himself.
> Personally, I always had a low opinion of people who feel that they
> can win arguments merely by declaring credentials.
>> >Homunculus reinvented? The little-man-in-the-cell "using" a blueprint
> >while IT ("he") constructs more cells and eventually a person?
>> The homunculus is your invention. I was giving an analogy for the
> process.
>
Actually, the old battle between preformation and epigenesis hasn't ever
stopped, it has just taken on a new guise. The "homunculus" may relate to the
notion that the "blueprint" is preformed in DNA (or cytoplasm). Epigenetics,
as a view of developmental processes, emphasizes cell-cell interactions and
downplays direct involvement of the genes. These interactions result in cells
expressing only a subset of their DNA as they reach their final phenotype.
The interplay at the somatic level dictates what will transpire at the
genetic level. In this view, genes, although still the bottom line, are
ancillary, kind of like grunts fighting in the trenches, while the generals
discuss higher level strategies.
My understanding of development is incomplete. I'm approaching development
from the evolutionary standpoint, which has interesting repercussions, which
I'll have time to explore further when this term is over.
>> >Poor metaphore. How about this one (it has its own flaws, but at least
> >it is different): is the cell like a computer "using" DNA like a
> >program? or is the program "using" the computer? (Not QUITE the same
> >question as "is a chicken an egg's way of making another egg?", but
> >reminds me of it...)
>> Neither of those works. They naive oversimplifications. I suggest
> "Lifelines: Biology Beyond Determinism" by Steven Rose for a more
> realistic view of the relation between DNA and organism.
>
I'm assuming these ways of thinking shadow Richard Dawkins' gene-centric
approach in _The Selfish Gene_ (1976), where organisms are vehicles shuttling
genes through the generations. This issue is far too complicated to delve
into right now, but I think the organism's phenotypic integration overrides
"selfish gene" effects. This is more of a Mayrian approach. I suggest reading
Ernst Mayr's chapter about development in his book _This is Biology_ (1997).
It is quite a cogent approach and he begins to delve into evolutionary
implications of development. An in depth book is Brian Hall's _Evolutionary
Developmental Biology_ (1992). He goes into the preformation versus
epigenesis dichotomy and covers a lot of ground in many other topics. I'm
presently trying to find time to read Brian Hall's book _The Neural Crest_
(1988) with a special treat (Sven Horstadius' monograph on the neural crest)
included. The neural crest issue touches on another problem (the germ layer
theory) but we won't go into that right now :-) It is sufficient to say that
the development of the neural crest has had profound evolutionary
implications.
>> >Bottom line: no substitute for the painstaking moment by moment
> >analysis of develomental interactions. Those who undertake this
> >analysis are not the strawmen Rickert imagines.
>> LeFever can't read. I have not used the term "strawmen" to refer to
> actual persons. My criticism has been of the extreme version of
> genetic determinism that Scanlon has been preaching, not of people
> doing genuine research.
>>
Aren't vertebrates indeterminate or regulative in their development? BTW, I
prefer the term "influence" to the term "determinant". I see things from a
multifactorial perspective.
I think the "developmental interactions" are very important. It is possible
that the "blueprint" or what some call the Bauplan (e.g.- Wallace Arthur in
_The Origin of Animal Body Plans_ (1997)) or what Ernst Mayr calls the
"somatic program" (see _This is Biology_(1997) or Mayr's 1994 paper
"Recapitulation reinterpreted: the somatic program".The Quarterly Review of
Biology. (69): 223-232) drives the development of an individual, with the
genetic program playing second fiddle.
The somatic level (or epigenetic) view does not negate the role of genes, it
just emphasizes the role of a cell's interaction with its environment (other
cells, extracellular matrices, growth factors, etc.). Some genes may be more
significant than others in aiding the generation of body plans, with a
temporal consideration of gene effects. I'd like to explore the homeobox
angle, but it will have to wait. I'd also like to take a look at the
pharyngula, with its wondrous dorsal hollow CNS rudiments.
Sorry for jumping in on this thread, but it started to touch on some issues
I've been reading lots about, and still have lots more to read. When I get
more time (Christmas break) I'll immerse myself in evolution/development and
try to bring some neuro into the picture. -- Scott Chase (note followups at
anthym at webtv.net)
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