Text 130, 222 rader
Skriven 2004-09-22 13:39:00 av Anthony Cerrato (1:278/230)
Ärende: Re: Self-Organization and
=================================


Great article--and comments. Much room for thought.
.....tonyC

"Michael Ragland" <ragland37@webtv.net> wrote in message
news:cipq83$1gqt$1@darwin.ediacara.org...
>
>
> Computational Geneticists Revisit A Mystery In Evolution
> Science Daily ^  | Date:Posted 8/8/2002 | Editorial Staff
> Posted on 08/16/2002 10:27:48 AM PDT by vannrox
> Reprinted from ScienceDaily Magazine ...
> Source: Stanford University
> Date Posted: Thursday, August 08, 2002
> Web
> Address:
http://www.sciencedaily.com/releases/2002/08/020807065302htm
>
> Computational Geneticists Revisit A Mystery In Evolution

[snipped article]

> Comment:
> This is an article which flirts with self-organization of
complex
> biological systems although the term isn't used. It
acknowledges, "That
> doesn't mean natural selection doesn't play an important
role. Continues
> Petrov: ''Natural selection has shaped the genetic
networks of complex
> organisms so that they produce appropriate phenotypes -
the more highly
> interconnected these networks are, the more robust the
corresponding
> phenotypes are. The importance of this result is that it
shifts the
> focus of the field away from abstract models of natural
selection and
> toward actual genetic networks. In so doing, it will
provide a new
> perspective for analyzing and understanding the current
outpouring of
> genetic data in model organisms.''
>
> But the article states, "Second, modeling has shown that
if nature
> ''selects'' a trait, canalization evolves - but very, very
slowly, over
> millions and millions of generations. ''When you start
thinking about
> time scales like that,'' Siegal says, ''you have to wonder
whether any
> evolutionary force can be consistent over that amount of
time to
> actually cause the outcome that you see.'' To back this up
the article
> states, "And third, what's ''optimal'' today may not be
optimal
> tomorrow. Says Bergman: ''As [scientist Stephen Jay] Gould
said, as the
> environment changes what was once fit may not be fit
today, and with
> further change in the environment could become fit
again.'' IMHO this is
> nonsense. I would argue that for millions and millions of
years despite
> intermittent dramatic changes in environment there were
traits which
> were naturally selected (in conjuction with developmental
genetic
> regulatory networks) which were canalized and conserved
across species.
> Some animals became extinct for various reasons but these
traits were
> canalized and conserved across species.
>
> Siegel states, "In many ways canalization was sort of a
smokescreen that
> was dividing evolutionary biologists and developmental
biologists. The
> developmental biologists were studying their genetic
networks and the
> evolutionary biologists were in the abstract saying,
'Well, these
> networks must have evolved to produce certain properties,
like
> robustness in the face of mutational insult.' But since we
have shown in
> our model that it's actually the nature of the
developmental system that
> can give you this property, they're really not two
separate things to
> study. They're the same thing to study. I think a lot will
come out of
> looking at actual genetic networks and how the structure
of those
> networks gives them the property of being robust.''
>
> I agree although not alot of information was given on
their model and
> the results of it. But I would not call canalization a
"smokescreen".
> The idea of certain traits being evolutionarily conserved
[canalized]
> via natural selection and developmental genetic networks
contributing to
> this canalization is IMHO very real.
>
> The article leans very much against natural selection. It
states,
> "Scientists used to think that developmental fidelity
evolved via
> natural selection, principally through survival and
reproduction of
> organisms with redundant genetic systems - that is, ones
with copies of
> important gene sequences. But Siegal and Bergman's results
indicate that
> redundancy may only be one small manifestation of a bigger
theme: the
> complexity of gene networks. In short, more complex
systems are more
> resistant to change in their outputs." This is very
troubling to me if
> true. I wouldn't characterize redundancy as a small
manifestation in the
> sense such canalized traits which have been conserved
across species
> [such as aggression] allowed many species to survive,
reproduce and
> evolve over millions and millions of years. But it worries
me if these
> canalized traits are part of the developmental complexity
of gene
> networks and are more resistant to change in their
outputs. I've stated
> aggression in humans is no longer an adaptive trait but if
it is a part
> of the complexity of gene networks and more resistant to
change in
> output than that means a much greater understanding of
these
> developmental gene networks in complex biological systems
will be
> necessary before possibly being able to remove aggression
through
> genetic engineering.
>
> Along the lines of self-organization the article states,
''It is
> typically assumed that important properties of organisms
are crafted by
> natural selection,'' says Dmitri Petrov, assistant
professor of
> biological sciences. ''What Siegal and Bergman show is
that robustness
> in the face of mutation, or canalization, may be a
byproduct of
> complexity itself and therefore that robustness may be
only very
> indirectly a product of natural selection.''
>
> It states, "Natural selection may be important in shaping
traits that
> aid in reproduction and survival, but Bergman and Siegal
show that it
> doesn't matter much during development, when, biologically
speaking, all
> roads lead to Rome." Who has said natural selection is
divorced from
> development. It goes on to say, "The puzzle that attracted
Bergman and
> Siegal was not so much the nature of the genetic switches
that operate
> at the ''forks'' [canalization] but instead what causes
the ''grooves''
> that keep development faithfully rolling along when both
environmental
> disturbance and genetic mutation could potentially set it
off course." I
> don't subscribe to the Garden of Adam and Eve. At one time
we were
> invertebrates and over millions and millions of years we
evolved to the
> present Homo Sapien. During that time there were
innumerable
> environmental disturbances and mutations and we evolved.
We share
> "genes" with flies, mice and many other creatures. But I
don't believe
> Siegel the complex nature of the genetic system itself is
going to give
> you canalization independent of natural selection. Yes,
this complexity
> goes beyond mere redundancy, incorporating all kinds of
elaborate
> connections in the gene network but this doesn't negate
natural
> selection.
>
>
>
>
> Copyright © 1995-2002 ScienceDaily Magazine | Email:
> editor@sciencedaily.com
>
> "It's uncertain whether intelligence has any long term
survival value.
> Bacteria do quite well without it."
>  Stephen Hawking
>
>
>
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