Re: Addressing Scientific Reductionism

Perplexed in Peoria wrote:

"Wirt Atmar" <atmar@xxxxxxxxxxxxxxxxx> wrote in message news:e09bu0$2gpu$1@xxxxxxxxxxxxxxxxxxxxxx

Robert Kolker wrote:


dkomo wrote:


Moreover, in a book I've just recently slogged through, _The
Plausibility of Life_, such modular organization has been strongly
selected by evolution because it greatly facilitates the process of
viable phenotypic variation. Organisms are modular because they can
evolve more easily if they are. A small amount of genetic change can
result in big changes in organism characteristics. No need for
Darwinian gradualism.

Now that is quite fascinating. That could very well account for
punctuated equilbrium. It is interesting to note there is much more to
(possible) evolutionary mechanisms than the sculptoring and culling done
by natural selection.

I am beginning to understand why thinkers like Dennett consider the
theory of evolution the greatest thing since sliced whitebread.

If you think about it for a minute, you will quickly come to the
conclusion that such a systems design is inevitable. The notion that
"one gene encodes one trait" was completely dispensed with by 1945
(although the idea remains implicit in mathematical genetics). Rather,
by the 1930's, it was becoming obvious that any complex character in the
phenotype was the result of the expression of a significant portion of
the genome.

If that's so, the question then becomes: "how do you evolve such a
structure?" If the interaction matrix between gene products and their
affected traits is such that everything affects everything, evolution
becomes impossible. The entire design becomes a house of cards. You
can't change any bit of code without affecting the entire organism.

The evolution of modular design ("organ-ization") is the only way out,
and it's advantages have been discovered independently by human
engineers and nature, albeit several billion years displaced in time.

Pleiotropy is the inevitable consequence of highly interactive systems.

One of the reasons I resist the ideology that life is inherently
modular is that it sometimes closes minds in advance of the evidence.
If we already 'know' that life is modular, then we will not find
the exceptions to the rule. Lipmann, for example, provided a nice
modular model for the production and use of cellular energy. But
it actually made it more difficult for Mitchell to convince people
that the situation is more complicated than that.

There is also the population genetics argument. Wirt writes:


If the interaction matrix between gene products and their
affected traits is such that everything affects everything, evolution
becomes impossible. The entire design becomes a house of cards. You
can't change any bit of code without affecting the entire organism.


Ok, but that is not an argument using natural selection at the organism
level for maximum advantage here and now. It is an argument appealing
to retaining the potential for future improvements.

If a species cannot easily evolve it cannot respond to environmental
changes and it will go extinct. Evolvability has itself been selected
"here and now". It is as key a trait of an organism as any trait. It
means an organism can more easily produce offspring with new characters
that can take advantage of changed environments. The rapidly evolving
beaks of the Galapagos finches are an example.

NS can take this
kind of criterion into account only if selection takes place at a
higher level - the species level, for example. And, population genetics
tells us that selection at that level must be fairly weak.


The evolution of evolvability and modularity does not depend on species
selection.

Hmmm. I wonder if what is 'wrong' with the pop gen argument is the
assumption that mutation is random and undirected?

In _Plausibility of Life_ the authors say variation "does not take place
in all directions" as in classical Darwinism. It occurs easily along
certain directions and not at all along others. For example, it is
rather easy to vary the limb structure of animals. It is next to
impossible to change a conserved core process like the splicing of
introns in eukaryotic cells.

The authors never discuss population genetics. They still accept that
mutation is random and undirected. It is the phenotypic result of that
mutation that is channeled. Variation is a *constrained* random walk.
The drunk cannot stager in any direction he pleases away from the lamp
post. He always staggers along particular alleyways.


--dkomo@xxxxxxxx




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Relevant Pages

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  • Re: Addressing Scientific Reductionism
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