On Sat, 16 Mar 1996, Brian Miller wrote:
>
> Denis writes
>
> >For too many years now biology has functioned with what I call a
> >"one-gene-one-trait" mentality, and employing this paradigm certainly
> >gives SOME just cause for a suspicion toward evolution (which, yes, to
> >a certain extent, justifies the criticisms Dr. Johnson et. al.)
Brian writes:
> Does not evolutionary theory demand a "one-gene-one-trait"
> mentality.
No. This is exactly the point of the new biology. There is
a very significant EPIGENETIC component to developmental biology (and
thus ultimately morphology), and it is by understanding this that
one can speculate on how dramatic change could have come about in evolution.
> The only way that evolution could produce a hierarchical
> pattern and "mosaic transitions" is if most major traits could evolve
> independently.
Good point here, but this problem is solved not by changing the gene
itself, but changing its relationship within a development program (eg, a
heterchronic mechanism) or its expression within a group of genes (eg.
notion of the HOX combinatorial code in limb development). Again, these
are all epigenetic mechnanisms. In other words, there would be no
pleitrophic "fallout."
> The fact that mutations causing major changes usually
> cause major changes in more than one structure (pleiotroy) would seem
> to prevent the possibility of certain structures changing, like a leg
> into a wing from reptiles to birds, while keeping other traits, such
> as the amniotic egg which is found in both reptiles and birds, the
> same.
Here is where I very much disagree with you and where shifting your
categories to developmental/molecular terms would quite change your view
of the limb and open you to the possibility of its evolution. For
example, when I look at a limb (for that matter, even a fin)
I don't see an osteology, a musculature, etc. (though these have been and
are helpful preliminary guides in defining homology). Rather, I see the
limbs/fins in terms of the ZPA, the AER, the HOX-D series and Sonic Hedge
Hog--all of which are present from fish to amphibians, reptiles,
birds and mammals. More specifically, the genetic code does not have a
"blueprint" for a bone like the humerus. Rather, it is the RELATIONSHIP
(specifically, the epigenetic relationships) of the previous
developmental structures that results in the shape of this bone--and it
is for this reason why there is such an amazing plasticity in the limb
system to allow it to take on so many forms.
In reflecting on this new biology I cannot help but get theological.
Isn't it interesting that the fin/limb system is SETUP this way? (And yes,
the passive voice is being used intentionally). Kind of like
the anthropic coincidences you physicists talk about, eh? Is it blind luck
that when the fin first showed up in evolutionary time it had a
developmental system with an incredible plastic potentiality that would
allow the hands of a Bach to evolve? Yes, a potentiality--not
exactly a notion amicable to Dawkins. Dare I called this an
example of a "BIOLOGICAL ANTHROPIC COINCIDENCE"?
> I believe Meyer's mentions in <Populations, Species, and
> Evolution> that most mutations are in fact pleiotropic, and the trait
> linkings do not at all fit within the evolutionary hierarchical
> pattern. Evolutionists seem to be ignoring pleiotropy when it does not
> fit into their theories and focusing on it when it does.
That is the whole point of the new biology--it is stepping away from
this one-gene-one-trait paradigm. But the reason it is doing so, is not
to solve evolutionary problems like the one you judiciously cite. First
and formost, this new work is trying to understand biological mechanisms.
Secondly, the fruit of a more complete understanding of biological
mechanisms is a better appreciation of how to apply them in evolutionary
theory. The fruitfulness of the new biology is that it is indeed solving
problems created by the one-gene-one-trait methodology.
Enjoyed the interchange.
In Him,
Denis
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Denis O. Lamoureux DDS PhD PhD (cand)
Department of Oral Biology Residence:
Faculty of Dentistry # 1908
University of Alberta 8515-112 Street
Edmonton, Alberta Edmonton, Alberta
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CANADA CANADA
Lab: (403) 492-1354
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E-mail: dlamoure@gpu.srv.ualberta.ca
"In all debates, let truth be thy aim, and endeavor to gain
rather than expose thy opponent."
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