lamoran{at}bioinfo.med.utoronto.ca (Larry Moran) wrote in
news:c8rd4u$o8g$1{at}darwin.ediacara.org: 

> On Sun, 23 May 2004 18:07:23 +0000 (UTC), A
> non.  wrote:
>> Larry Moran wrote:
>>> On Sat, 22 May 2004 02:26:53 +0000 (UTC), 
>>> Anon.  wrote:
>>>>Larry Moran wrote:
> 
> [snip]
> 
>>>>>In terms of total amount of evolutionary change, random genetic
>>>>>drift is the main mechanism of evolution, by far. Almost all
>>>>>evolutionary biologists know this.
>>> 
>>>>Doesn't that depend on how you measure evolutionary change?
>>>   
>>> I suppose. One could presumably eliminate or ignore some kinds of
>>> evolutionary change in order to make natural selection seem more
>>> important.
>>> 
>>>>At the sequence level, I would agree (well, until someone shows
>>>>me some evidence to the contrary).
>>> 
>>> Okay. So, if we take into account ALL evolutionary change then you
>>> agree that random genetic drift is the most important mechanism?
>>> 
>> I think I can still use my same question: Doesn't that depend on how 
>> you measure evolutionary change?  It's not clear to me that we have 
>> to measure it at the sequence level.  
> 
> I didn't say you *have* to measure it at the sequence level. I just
> said that when you take into account ALL evolutionary change,
> including change at the sequence level, then drift is the main
> mechanism. 
> 
>> If we measure it at the phenotpyic level, we get a different answer. 
> 
> Perhaps. What you are saying is that if we only look at *some* 
> evolutionary change then drift may not be the main mechanism of that
> subset. I'm sure you could find a subset of evolutionary change where 
> natural selection is the dominant mechanism. You could also find a 
> subset of evolutionary change where molecular drive is the main 
> mechanism ... or species sorting. What the point?
> 
>> Most paleontologists will probably 
>> take a phenotypic view, most geneticists will take a sequence point
>> of view.  Both are, I think, equally right, unless one defines
>> organisms purely as their sequences.
> 
> They are not both equally right if they claim different mechanisms for
> the majority of ALL evolutionary change. The only way the adaptionists
> can win such an argument is to claim that changes by random genetic
> drift are not evolution. Some of them try to do this. I don't think
> that's what you're trying to do, is it?
 

I know there has been a previous discussion on the definition of
evolution, and in many ways I can agree with the definition of any change 
in gene frequency as evolution, but I'm having difficulty resisting the
temptation of playing devil's advocate. 

Now first I would like to clarify something. Bob's original agreement was 
that drift is unquestionably the main mechanism of change at the sequence 
level. I also agree with this. However change at the sequence level is 
not evolution by the generally accepted definition of evolution as change 
in "gene" frequency, at least not until the change in sequence affects 
the function of the "gene".  

Now as to actual changes in gene function, as far as I know there is 
still debate as to the relative importance of  drift vs. selection in 
gene frequencies,  so I would have to take issue with your 
characterization "by far", although you may well be correct about 
"majority". 

But in either case:

Since the extent of drift due to sampling error is dependent on effective 
population size, and since effective population size is dependent on the 
niche, and since selection pressure is also governed by the niche, it is 
clear to me that  ecological niche development is the main mechanism of 
evolutionary change.

Yours,

Bill Morse
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