Guy Hoelzer  wrote in
news:bosf45$3fu$1{at}darwin.ediacara.org: 

> I have snipped most of this post because TT and I have both expressed
> our views effectively and our differences have been made clear.  It
> seems we are at an impasse on several points, and we can leave it at
> that. 
> 
> in article bor4uc$2ni3$1{at}darwin.ediacara.org, Tim Tyler at
> tim{at}tt1lock.org wrote on 11/11/03 9:06 AM:
> 
>>> To add a nod to the kind of work I am currently engaged in, it is
>>> easy to show with computational models that gene flow is necessary
>>> for the emergence of genetic divergence between subpopulations [...]
>> 
>> ? They cannot diverge genetically if they are completely isolated
>> from one another...?
> 
> The system cannot self-organize if there is no communication among the
> components (subpopulations in this case).  If you explore a
> computational model of evolution in a spatially explicit context, you
> can ASSUME lack of communication between subpopulations and divergence
> happens.  Of course you have only learned what you assumed in that
> case.  If you allow for limited gene flow among subpopulations in a
> stepping-stone model, or among locations in a more general model of
> isolation by distance, then you can observe emergence of spatial
> boundaries between gene pools that you did not assume. This way you
> can learn about how such local subpopulations can evolve without just
> a circular confirmation of an assumption.  Divergence among 
> subpopulations in this way requires gene flow. 


Fascinating! (I snipped the remainder which was more about the level of 
selection argument) One of my (and many others - I am not original in 
this)  "benchmarks" for evolutionary explanations (as some of you may be 
aware) is the cichlid fishes of Lake Victoria. Since there has not really 
been time for allopatry to work its speciation magic, the question is how 
do you explain the observed diversity ? What you seem to be claiming 
above is that you have a model that does this. 

One of the reasons I am particularly intrigued is that I have read 
elsewhere (and I wish I could remember where)  that much speciation 
occurs not at the fringes of a population but in the middle. This makes 
intuitive sense from one standpoint - one might assume that marginal 
populations are in fact only marginally adapted to their local 
environment, and might not be likely to survive if isolated from 
replacement from the main population. I have previously argued that (at 
least for all but large  macrofauna) relatively severe weather (the 1000 
year storm) can provide "mini-allopatric" conditions. But there is likely 
to  be at least some gene flow within recovering populations, so a model 
that can show divergence even with gene flow is enticing.



Yours,

Bill Morse
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