Text 88, 103 rader
Skriven 2004-09-17 16:37:00 av Tim Tyler (1:278/230)
Ärende: Re: Genetic Drift and Mut
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John Edser <edser@tpg.com.au> wrote or quoted:
> >Tim Tyler <tim@tt1lock.org>
> > > JE:-

> > > 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".
> 
> > TT:-
> > It won't work: 
> > Organisms with fatal or severely deleterious mutations will
> > still be selected against - as will organisms who don't
> > manage to produce any fertile offspring - despite the
> > best efforts of the managers of the experiment.
> 
> JE:-
> I agree that eventually selection must end the
> experiment for the reason you describe. I did
> mention that eventually this would happen.
> However, this fact underscores rather then 
> undermines what I am suggesting. My main point 
> was that my definition of Darwinian fitness can
> suspend Darwinian natural selection for 
> enough time to allow a test of random
> drift as evolution within an expanding
> population. [...]

You could certainly magnify the effects of drift.

A small population size helps with that as well.

> > TT:-
> > You can't eliminate selection - all you can do is
> > change the selection criteria.
> 
> JE:-
> I am arguing you can suspend Darwinian
> natural selection for a considerable period
> within a natural population allowing a test
> to refutation of the my definition of
> Darwinian fitness.

In practice, you'd have a *very* hard time dealing with any
severely deleterious mutations that popped up.  You would
likely find you had a few sickly individuals on your hands -
and making them have 2.4 kids (or whatever) would be challenging -
and so fitness equality would not be preserved.

This would most likely happen immediately - not after
a long wait for drift-induced genetic rot to set in.

> > > JE:-
> > > The population will deteriorate to such an
> > > extent that it will become impossible to enforce
> > > Darwinian fitness equality and Darwinian selection
> > > will force its way into that population to
> > > correct the dissolution caused by drift acting
> > > alone.
> 
> > TT:-
> > Yes - that sounds about right
> > In practice, you can't eliminate selection.
> 
> JE:-
> You can, for a finite period of time.
> This is enough to test to refutation
> my definition of Darwinian fitness.
> Also, I argue, it will be enough to
> refute the evolution by drift hypothesis
> which entirely dominates evolutionary theory 
> turning it into an irrefutable iron man
> theory on a par with creationism.

It sounds as though we all agree that drift has specific
effects on the popualation.  It acts to casue undirected -
and most likely in the long term deleterious - changes in
the population.

This seems to be much the same position as those arguing
that genetic drift causes significant changes in natural
populations, though.  How would observing the effects of
genetic drift (by magnifying it) refute their position?
-- 
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