On Sat, 28 Feb 2004 18:18:20 +0000 (UTC), 
William Morse  wrote:
> lamoran{at}bioinfo.med.utoronto.ca (Larry Moran) wrote in
> news:c1ikj8$2pkb$1{at}darwin.ediacara.org: 

[snip]

>> Tim seems to be making the default assumption that most 
>> morphological features are due to natural selection. Dawkins 
>> certainly makes that assumption. Is this valid? 
> 
> Haven't we had this debate before on sbe? I believe it was termed 
> at that time the "null hypothesis" rather than the "default 
> assumption". My personal opinion, FWIW, is that we can make a good 
> first guess about a trait without the need for a default. 

Yes, I think we've debated this before on sbe.   :-)

Is there a rule about not bringing up the same topic again? It 
seems to me that there are a some topics that seem to be "debated" 
over and over again on this newsgroup so I assumed that this was 
okay.    :-)

Seriously, I think it's more interesting to discuss adaptionism and
random genetic drift than some of the other things that are taking
up time on sbe. Do you agree?

> If the trait shows little
> variation throughout a large population or is strongly correlated with
> an obvious environmental variable, and has an obvious relation to an
> aspect of species behavior, one can make the default assumption that it
> is an adaptation, especially if it has existed for a long period.(Again 
> based on recollection, Wirt did a much better job than I just did of 
> defining what traits could be considered adaptive as a default).
> Examples would include large ears in elephants, skin color in humans, and
> almost any morphological feature of horseshoe crabs. 
> 
> If the trait shows
> wide variation throughout a population regardless of environmental
> variables, or is confined to isolated subpopulations with no obvious
> relation to fitness, one can make the default assumption that it is due
> to drift. Examples include coat color in domestic cats and the Rh- blood
> type in humans. 

Hmmmm .... I would have thought that ear size in elephants and skin
color in humans were excellent example of drift. Don't you see how
difficult it is to make general rules? Your decision about what the
"default" hypothesis should be depends to a great extent on your
original biases. This is exactly the point that Lewontin and Gould
made in their original paper. If you tend to emphasize natural
selection in your thinking about evolution then you will look to 
adaptive explanations ahead of non-adaptive explanations.

> Note that I am cheating somewhat, as I am assuming there is at 
> least some data available to make a "default" assumption. 

Part of the problem is that even the selection of "data" has 
built-in biases. If you are an adaptionist, and you prefer an
adaptionist explanation, then you go looking for data to support
your assumption. For example, if you think human skin color is
adaptive then the only "data" you quote is the little bit that 
might explains why people with white skin lived in Northern Europe.

> Also, the above _are_ only default assumptions - either may be 
> proved false by better data, so ultimately I agree with Bob.  
> Also note that there will be a lot of traits - morphological 
> features and otherwise - that will not fall into either category.  
> In this case the adaptationists (including myself) will dream up 
> unsubstantiated Just So stories to which the drifters (sorry -
> the term has both a nice slightly pejorative ring to my ears as 
> well as reminding me of the 60's rock band) will recoil in 
> horror :-)  

No offense. I'm a drifter in the sense that it's part of my 
self-proclaimed "mission" to educate people about the importance 
of random genetic drift and evolution by accident. I'm not having 
much luck on sci.bio.evolution. This newsgroup is heavily dominated 
by people who reject the very concept of drift or who have deliberately
chosen not to understand it. I find this very strange in a newsgroup 
that's supposed to be devoted to discussing evolution at a serious 
level.



Larry Moran
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