On Thu, 26 Feb 2004 16:44:29 +0000 (UTC), 
Anon.  wrote:
> dkomo wrote:

[snip]

>> We have plenty of "just so" stories to explain each and every
>> purported adaptation.  Any amateur evolution theorist can come up with
>> half a dozen armchair explanations for each such trait.  What we don't
>> have in most cases is empirical proof that a particular feature of an
>> organisn is indeed an adaptation to the environment.
>> 
> Yes, so we need empirical observation to resolve this argument.  My 
> point is that we know that spatial and temporal variation in selection 
> pressures occurs, so we can't rule them out just because we don't like 
> them.  

Right. We also know for a fact that random genetic drift occurs so 
you can't rule it out just because you don't like it.

> Examining their effects is difficult (I've looked at both.  One 
> study needed a 60 year time seies, the other merely a crossing 
> experiment with a couple of thousand frogs).

Nobody said it was easy to prove natural selection or random genetic drift.
The key point to keep in mind is that in the absence of proof for one
mechanism or another you have to keep an open mind and not just assume
that it's your favorite mechanism that works.

It's easy to make up "just-so" adaptionist stories. The tricky part is
realizing that they are just stories and not real explanations.

>>>Of course, drift may also be an explanation, but I believe that we can
>>>only separate out the contributions of the different causes empirically.
>> 
>> It may be that many features of organisms are incidental and play no
>> role in their evolution.  That doesn't necessarily imply that these
>> features are subject to drift.  

If the features are not adaptive then they must be neutral (or nearly 
neutral). If the aleles for these features are neutral with respect to
fitness than there frequency in the population *will* be subject to 
random genetic drift. You can't stop it.

>> Drift is a phenomenon of small, isolated populations.

This is an incorrect statement.

> And there are a lot of them about, even in organisms like insects.

Exactly right. In the real world it's almost impossible to have a large
population of randomly mating individuals (i.e., panmitic). Almost any
population that you can think of is subdivided into a large number of
much smaller sub-populations that are more-or-less genetically isolated
from each other. This is obvious in humans but it's true of every other
species as well.



Larry Moran
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