From: adpeters@sunflower.bio.indiana.edu (Andy Peters)
Subject: Onar is probably right (was Re: Clarification)
Organization: Program in Evolution, Ecology, and Behavior, Indiana University
Date: Wed, 14 Oct 1992 04:51:43 GMT

Yes, you read it correctly:  Onar is probably right.  Given his assumptions,
the mechanisms he proposes are likely ones.  Let's take a look at his
assumptions, though:

ASSUMPTION #1:  MUTATION IS THE ONLY SOURCE OF GENETIC VARIATION (this
assumption is not critical to his model, but it's there (and wrong) all
the same)
Another source of variation, which cannot be ignored, is that due to 
recombination.  In sexual species, this is an extremely important 
mechanism by which immediate variation occurs.

ASSUMPTION #2:  THE DYNAMIC RANGE OF A SYSTEM IS NOT BROAD ENOUGH TO
ACCOMODATE "SEVERE DIVERGENCE" OF LINEAGES
Since you cannot even begin to predict what this complex range is, why do
you assume it to fall magically at the point at which macroevolution
begins?  Yes, we all agree that mere changes in the nucleotides of a genome
without changing the size of the genome necessarily gives a finite number
of possible outcomes.  But why do you insist that it is impossible to
get "severe divergence" within the dynamic range?  I'm sure most of
us here would be willing to stipulate that you're right with your
extreme example of the bacterium and the dog, but you can't even prove
_that_ with your "dynamic range" concept, because you can't even
begin to quantify it.  Your "dynamic range" is eerily similar to the
creationist's "kind."

ASSUMPTION #3:  GENE DELETIONS ARE LETHAL/DISADVANTAGEOUS AS A RULE
Look up neoteny, paedomorphosis, and the evolution of direct-developers from
larval-developers (Raff & Kaufman's _Embryos, Genes, and Evolution_ is a
good source).  In neoteny and paedomorphosis, what was the ancestral larval
form becomes the mature form.  In other words, many of the genes coding
for transformation to maturity are lost.  The evolution of direct development
is the other way around:  the organism is born as the mature form, and
most of the genes coding for larval traits are lost.  There are lots of
examples of both; the ones I can think of off the top of my head are
the axolotl for neoteny and a sea urchin for direct-development.

ASSUMPTION #4:  CHANGES IN GENE NUMBER (ADDITIONS OR DELETIONS) NECESSARILY
IMPOSE "GENETIC INSTABILITY"
The important thing about the gene deletion examples is that, 
counter-intuitive as it may be, messing with the early development 
of an organism _doesn't_ necessarily wreak havoc on the rest of 
its phenotype.  To put it in Onar's terms, the loss of these genes 
doesn't cause any more of a genetic instability than do mutations 
within the original "dynamic range."

In addition, there is no reason to believe that the addition of new genes
necessarily causes "genetic instability" in the Aam sense (i.e. leading
somehow to an increased susceptibility to selection).  Take for example
the most extreme form of gene addition:  the evolution of polyploidy.
My advisor has triploid snails which he can't tell apart from diploid
except by electrophoresis.  No "genetic instability" is in evidence, nor
is there particular evidence of an expanded dynamic range.

This assumption is the crux of the biscuit:  if Onar can't show *with*
*empirical*data* that changes in the number of genes necessarily cause
more "genetic instability" than do mere changes in pre-existing genes,
his model collapses.  I don't think he can do it.

ASSUMPTION #5:  PUNCTUATED EQUILIBRIA HAVE BEEN PROVEN; "GRADUALISM" HAS
BEEN DISPROVED
(I just though I'd throw this one in here.  It really doesn't affect
his model at all, but it is an incorrect assumption Onar makes.  At least
I left out his assumptions about chaos theory and our understanding of
it.)

So, what do we have?  Unless Onar can support his assumptions (particularly
#2 and #4) with data showing that biological systems really work the
way he insists they must, I figure his model tells us that there
must have been changes in gene number sometime during evolutionary history.
Wow, pretty earth-shattering, huh?

>Onar.

-- 
* Andy Peters                     * "Slugs are small and portable    *From
* Program in Evolution,           * Just stuff 'em up your nose      *"Slugs,"
*      Ecology, and Behavior      * They'll fit beneath your armpits *by David
* Indiana University, Bloomington * Or right between your toes"      *Greenberg