Guy Hoelzer wrote:
> in article c4ntrv$24q5$1{at}darwin.ediacara.org, William Morse at
> wdmorse{at}twcny.rr.com wrote on 4/3/04 8:02 PM:
> 
> 
>>Guy Hoelzer  wrote in
>>news:c3pmuf$1opn$1{at}darwin.ediacara.org:
>>
>>
>>>in article c3f4tm$1h9d$1{at}darwin.ediacara.org, William Morse at
>>>wdmorse{at}twcny.rr.com wrote on 3/19/04 7:51 AM:
>>>
>>>
>>>>Guy Hoelzer  wrote in
>>>>news:c3dade$tfa$1{at}darwin.ediacara.org:
>>>
>>>>>Hmmm.  Can you name one example of an "observed phenotypic
>>>>>difference" for which drift would not qualify as a
"default"
>>>>>explanation?
>>>>
> [snip]
> 
>>>>You can probably give an equally long litany of examples of
"drift".
>>>>This is exactly my point. You argued in another follow on this thread
>>>>that neutral drift should always be the null hypothesis. I disagree
>>>>strongly with that statement. Both drift and selection always occur,
>>>>but their influence differs in different circumstances. I think we
>>>>know enough about evolution to recognize when one or the other is
>>>>_likely_ (note emphasis) to be dominant. So we do not need to posit
>>>>one or the other as a universal default.
>>>
>>>I think we agree more than disagree here.  My comment about the
>>>default or null explanation applies only to the context in which drift
>>>and selection are assumed to be independent "forces."
>>
>>I also think we agree more than disagree, and how the heck can we have
>>any fun with that? But to clarify - did you mean "independent" or
>>"competing"? To my mind drift and selection _are_
independent, but they
>>are not _competing_ in the sense that competing would imply that the
>>evolution of a trait must be due to one but not the other.
> 
> 
> 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.

Bob

-- 
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax:  +358-9-191 22 779
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
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