Modularity - was: Addressing Scientific Reductionism


"dkomo" <dkomo871@xxxxxxxxxxx> wrote in message news:e0c0c7$he2$1@xxxxxxxxxxxxxxxxxxxxxx
Perplexed in Peoria wrote:
[Whether there can be selection for modular organization]
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".

I think you are still making a species-level selection argument.
In organism-level selection, as I understand the term, an organism
doesn't really 'care' whether its species goes extinct somewhere down
the road. It 'assumes' that density dependent selection will
prevent the extinction. And anyways, the organism still 'wins'
in this viewpoint if its descendents are the last survivors.

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.

You are assuming that if the finches had not evolved, they would
have gone extinct. I'm not sure that is true.

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.

I continue to disagree. Except as I discuss in the next (snipped)
paragraph.

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.

Right. My suggestion is in accordance with those of the "Plausibility"
authors and of Gould. 'Constraints' can destroy many classical pop
gen arguments by subtly violating the assumptions embedded in the
pop gen models.

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.

And therefore his staggering is not random in some ways, though it
remains random in other ways. Randomness is an EXTREMELY subtle
concept, and many of the disputes concerning randomness arise because
people are using the word in different ways.

We seem to be mostly in agreement here regarding the biology. My
responses are mostly a quibble regarding the language you use in
describing our common agreement. I claim that if random mutation
is assumed, then species-level selection is needed to produce
modularity. But then, in some sense, the mutation may not be
random, so modularity can arise anyways, even if the pop gen people
don't approve.


.

Relevant Pages

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