"Anon."  wrote in
news:c4uknh$154c$1{at}darwin.ediacara.org: 

> Guy Hoelzer wrote:

>> I meant that drift should be treated as the default or "null"
>> explanation for the evolution of any in the absence of evidence to
>> the contrary, as long as drift and selection are treated as mutually
>> exclusive alternatives.  With regard to allowing for multiple
>> causation, I would extend my argument to say that the null
>> explanation should be 100% drift and 0% selection.  An assertion that
>> selection has had effect ought to be backed with evidence, although
>> no such requirement should be attached to drift, which I assert is 
>> universally and unquestionably at play.
 
> Hmm.  I think that's a bit of a simplification.  I doubt that drift is
> very important in barley mildew (Ne = infinity, to a good 
> approximation).  I think claiming that any allele frequency changes
> are due to drift will get you laughed at (well it would do if most
> mildew biologists weren't too polite).
 
> I can't see why we have to stick to a single null hypothesis no matter
> what the organism or context.  Actually, I'm not a big fan of
> insisting on null explanations anyway - read Fisher & Ford 1947
> (Heredity 1: 143-174) if you want to see what will happen.


I agree with Bob. The whole point of my original jumping in on this 
furshlugginer thread was that we can do better than insisting on either 
drift or selection as a null hypothesis, since we know that drift and 
selection are not in fact mutually exclusive, but we also know that the 
expected magnitude of their effects on allele frequencies in a given 
population is strongly dependent on effective population size, as Bob 
noted. There is no need to "assert" that drift is universally at play - 
it _has_ to be given the mechanism of genetics. But given the fact of 
excess reproduction and the same mechanism of genetics, selection is 
_also_  inevitable. Thus the only evidence needed to assert that 
selection has had effect is that there is excess reproduction. You would 
have to deny that statistics describes the real world in order to argue 
that either does not occur, and Bob would probably get really mad if you 
did that :-)

I would rant on, but Larry Moran in his recent follow already did a much 
better job than I can of summarizing the drift/selection debate. 
Unfortunately the odds of his convincing those who refuse to accept drift 
as significant appear to be exactly the same as my odds of moving the 
debate past the either-one-or-the-other-but-not-both stage, namely slim 
and none. 


Yours,

Bill Morse
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