Text 70, 114 rader
Skriven 2004-09-15 21:58:00 av Brett Aubrey (1:278/230)
Ärende: Re: Genetic Drift and Mut
=================================


"John Edser" <edser@tpg.com.au> wrote in message
news:ci7mqg$24lo$1@darwin.ediacara.org...
> Brett Aubrey <brett.aubrey@shaw.ca> 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". This being the case, RN's
> proposition (which is the standard Neo Darwinian
> position) that genetic drift can, on its own, cause
> evolution can now be tested. My prediction is that
> drift acting without selection can only cause the
> dissolution of each selectee within that population.
> 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.
>
> The simple truth is, genetic drift as just a
> random process, cannot validly constitute
> evolution without selection. However selection
> could cause evolution without genetic drift.
> This is easy to see as just a thought experiment.
> Genetic drift is not evolution it is temporal
> variation.  When you allow just a random process to
> become  causative to evolution in its own right without
> the aid of any non random process then evolution
> is reduced to just an "iron man" theory. This
> means it becomes irrefutable. In Popperian
> epistemology such a view cannot be tested
> and has no more or less to offer than creationism.
> In short, gene centric Neo Darwinism, in its
> wisdom, has, misusing the drift argument, reduced
> the status of evolutionary theory to non
> testable, i.e. puts it on a par with creationism.
> No wonder schools are being requested to teach
> "creation science" all over the USA. "What
> is good for the goose is also good for the
> gander". I cannot imagine how much lower
> evolutionary theory could degrade itself..
>
> > BA:-
> > Thanks muchly.  This is now making sense.  Is there any
> > quanification (or guidelines) of what constitutes a "small
> > population" with regards to genetic drift?
>
> JE:-
> I would request Brett to think again.

Thanks for your input.  Note that RN also pointed me to Wikipedia in his
response and my comfort came from looking at both sources.  I understand
that genetic drift is *a* mechanism (not the only mechanism) that acts in
concert with natural selection, and that mutation is another (Is this
right?).

And I think I get what I was missing previously - mainly how genetic drift
differs from mutation - that is, while they are both aspects to the "genetic
composition" that can change, genetic drift relates to allele frequency
changes and which alleles predominate, while mutation relates to errors in
copying DNA (Is this close?)
Regards,  Brett Aubrey.

> Regards,
> John Edser
> Independent Researcher
>
> PO Box 266
> Church Pt
> NSW 2105
> Australia
>
> edser@tpg.com.au
>
>
>
---
ū RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info@bbsworld.com

---
 * RIMEGate(tm)V10.2á˙* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 9/15/04 9:58:06 PM
 * Origin: MoonDog BBS, Brooklyn,NY, 718 692-2498, 1:278/230 (1:278/230)