Re: An epigenetic model of loss and vestigialization of limbs in

On Mar 9, 4:51 pm, CNCa...@xxxxxxx wrote:
On Mar 9, 12:11 am, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:

<CNCa...@xxxxxxx> wrote in messagenews:789baeac-261b-406e-90f9-d8ef3be439a0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Mar 7, 10:40 am, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:

<CNCa...@xxxxxxx> wrote:

[snip]

I see it differently for two reasons:

1. The whole process of early development is an epigenetic
process directed not by genome or zygotic genes, but by
the epigenetic information. This is what standard books
of the developmental biology and  leaders of the field say
(I don't consider it necessary to repeateddly cite them always
here). Even John believes that the development is epigenetically
regulated.

2. (Related to the "enigma of heredity"). The development of
the nervous system is an epigenetic process, based on
epigenetic information, which implies selective use of the
genetic information in the process of cell differentiation,
growth and reproduction.  Formation of the first operational
CNS at the phylotypic  stage is determined by the epigenetic
information deposited in gametes (cytoplasmic factors,
centrioles, centrosomes and the microtubular and cytoskeletal
structures that form under their control without which no
reproduction of genetic material and its ordered & equal
distribution in daughter cells can occur).

I see it necessary to remind the fact that for erecting the
complete CNS structure of billions/trillions of bits of higher
vertebrates, e.g., is invested an amount of information of
quadrillions of bits, which exceeds the amount  of the total
information in the whole human genome by six orders
of magnitude and is generated by the functioning CNS
after the phylotypic stage.

The only increase in "information" in the CNS is stored environmental
information, that is, the information which the organism "learns"
during its lifetime. The neural system itself is formed by a growth
of cells under a set of simple rules for growth, typically followed by
paring back under other simple rules (use it or lose it being one such
rule). More cells does not result in an increase in "information".
Each differentiated neural cell (like *all* differentiated cells) uses
only part of the genetic information available in the genome and thus
represents a *loss* of previously available information.

Think of it as a cellulose sponge. The sponge is formed by simple
chemistry. Some sponges are bigger. Some are smaller. But the
information required to make them is simple and does not change
between bigger and larger sponges. But you can add colored drops of
water one at a time to the sponge, producing a complex color scheme
(until diffusion occurs, but pretend that the drops stay where they
are placed). At the end you would have a much more "information"
complex system than you started with. The rules for connecting a
simple neural system are not significantly different from forming a
more complex one. Just more.

Evidently any idea that a genetic model can better
account for the erection of the CNS is fictional  not
only due to the above quantitative impossibility but
also for a qualitative one that there is no imaginable way
how the triplete code for amino acids could determine
the establishment of quadrillions of  SPECIFIC connections
betwen neurons (~10,000 for each neuron).

Neural connections are not rigidly *planned* or present as some sort
of rigid blueprint. The connections form by virtue of the following
of simple growth rules. The connections that form by these simple
rules then *become* further specified by useage. That is, by
*learning*. That is, more of the same (cells and connections), allows
storage of more information. It is this flexibility that allows stroke
victims to sometimes regain speech and function. And why, after you
burn your finger, you wind up with sensation after recovery.

The point that you fail to understand is that all that *environmental*
stored information acquired by *learning* during the life of the
organism will be lost when the organism's soma dies (unless they teach
it, nongenetically or culturally, to the next generation) because
there is no general mechanism that transmits *acquired* information
between generations (maternal effects excepted, but those are
Mendelian (aka genetic) factors). Organisms can transmit,
genetically, the *capacity* to learn by *genetically* being able to
generating an organ like the brain and CNS that is capable of
"sensing" the environment and, chemically, that can take this
environmental information and can produce appropriate changes in
organismal behavior, biochemistry, or even morphology. There is no
general mechanism to heritably transmit such precise learned behavior
through the gametes however. The history of trying to find a
mechanism for the inheritance of acquired characteristics has
uniformly been one of failure.

Neurobiologists tell us  that these specific connections
are determined experience-independently by the
spontaneous activity during the whole post-phylotypic
development and experience-dependently fine tuned
during the whole postnatal life.
Is there any visible reason to think they are wrong?

That is what I described. The initial connecting is done by following
simple growth rules, largely generated by mutual induction of nerves
and tissues to be innervated. Subsequently, we have activation of
some connections and loss of others. This is done by tissue that is
using only a fraction of its potential genetic information (because
that information must also be capable of producing *both* male and
female anlagen, liver cells, stomach lining, dermis, cardic muscle,
etc).

[snip]

.

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