John Edser wrote:
> Brett Aubrey  wrote:
> 
> 
>>>RN:-
>>>snip<
>>>In a small population, it is quite possible (even very likely) that
>>>the abundance of a particular allele might change just be chance over
>>>generations.  For example, those individuals with big noses just
>>>happened to have more babies with big noses than expected.  It is sort
>>>of like flipping a coin twice. You expect one head, one tail, but
>>>sometimes you end up with two heads. That is the definition of genetic
>>>drift: a change in the genetic composition of the population (in the
>>>allele frequencies). 
>>
> 
> JE:-
> Of course, RN has _not_ eliminated Darwinian natural
> selection from the proposed drift process so that RN's
> conclusion that genetic drift is alone causative remains 
> incorrect. Clearly, if "those individuals with big noses just
> happened to have more babies with big noses than expected"
> and raised more big nosed offspring to fertile adulthood
> then any assumption that "just happened" was ONLY chance
> remains utterly incorrect.
> 
> I have described an experiment that can eliminate all
> natural selection within an _expanding_ population 
> only allowing genetic drift as causative to allele
> freq. changes. All you have to do is artificially
> force all members of one population to raise the
> exactly the same number of fertile forms to adulthood
> where this number is larger than just a parental
> replacement value.  The prediction is: all natural 
> selection must be halted within this experiment while 
> Darwinian fitness equality can remain enforced. Thus only 
> genetic drift (which cannot be eliminated) is now left 
> to cause "evolution". 

No, you've deleted drift as well.  The only way drift can be 
re-introduced is for there to be genetic variation within a family 
(through segregation), but in this case you can no longer guanrantee 
"Darwinian fitness equality".  In other words, this doesn't allow you to 
have your cake and eat it.

If you want to eliminate drift, then you need an infinite [effective] 
population size.

Bob

-- 
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 68 (Gustaf H„llstr”min katu 2b)
FIN-00014 University of Helsinki
Finland

Telephone: +358-9-191 51479
Mobile: +358 50 599 0540
Fax:  +358-9-191 51400
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
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