On Tue, 18 Feb 2003 15:52:22 +0000 (UTC), jimmcginn{at}yahoo.com (Jim
McGinn) wrote:

>jae{at}veni.ucdavis.edu (Jason Eshleman) wrote 
>
>
>> >Okay. Would it take a text book to tell me why drift occurs (feel free 
>> >to recommend one if it would ;-)?
>> 
>> Drift is simply sampling error.  It's change due to chance and chance
>> alone, blind to the genetics.  If you have a population that is 50-50 for
>> 2 alleles at a locus, in the next generation, it may not be 50-50 just
>> because one or two individuals with one genotype reproduced more simply
>> due to chance.  Or because a disaster wiped out a ton with one genotype
>> (the disaster being blind to the genotype--thus it's not selection for
>> that type).  
>> 
>> Chance is always a factor.  
>
>To even discuss genetic drift as a factor in speciation is 
>to demonstrate one's ignorance of speciation.  
>
>I'm going to make my argument by way of analogy:
>
>Suppose that instead of being concerned with speciation we 
>were concerned with the level of the oceans and changes 
>thereof.  If one went out to measure the level of the ocean 
>one would observe that their measurement went up and down 
>on a second by second basis.  Why?  Because of waves.  So 
>the observation that the level of the ocean changes on a 
>second by second basis is confirmed by observation.  However, 
>if you were to attempt to gain an understanding of why ocean 
>levels change over thousands of years the fact that oceans 
>have waves would be perfectly useless.  Levels of oceans 
>change depending on inputs (melting of glaciers) and outputs 
>(formation of glaciers).  
>
>likewise genepools (populations) change over time due to 
>natural selection not genetic drift.  Genetic drift is nothing 
>but the OBSERVATION that gene totals change due to random 
>factors over time.  Like waves on an ocean the changes in gene 
>totals that result from genetic drift are irrelevant to 
>understanding why new species emerge.  To say otherwise is 
>equally ridiculous as saying that sea levels rise and fall as 
>a result of waves.
>
>One must be extremely careful about the truths that one 
>extracts from college level text books.  Half of it is 
>superstition and the other half is half superstition.
>
>Unfortunately this is just the state of the current paradigm 
>in evolutionary biology.  
>
>Jim

To say that genetic drift is a cause of speciation is, indeed,
incorrect.  But to say that genetic drift is a cause of evolution is
another matter indeed.  Genetic drift is definitely one of the
important mechanisms of evolution, a change in the genetic composition
of a population over time.  Given that populations do change by means
of a variety of mechanisms (including drift, selection, mutation, etc)
then additional factors such as the development of a reproductive
isolating mechanism as one of the changes will indeed produce a new
species.

I haven't followed this thread from the beginning so I don't know just
what point you are making about ocean waves.  However, if I plot the
level of the surface of the ocean at one particular point against
time, then ocean waves are indeed one source of variation.

There are reasons why the mean level of the ocean remains relatively
constant even though waves tend to cause variation.  However, there is
no reason why an allele frequency should remain constant when subject
to random variation. Random walks can cause significant shifts in
position in all sorts of physical processes and result in major
macroscopic phenomena (diffusion, for example).  Evolution is no
different.
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