Text 303, 109 rader
Skriven 2004-10-03 22:27:00 av Tim Tyler (1:278/230)
Ärende: Re: Testing Evolution Via
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John Edser <edser@tpg.com.au> wrote or quoted:
> Tim Tyler <tim@tt1lock.org> wrote:-

> > > > TT:-
> > > > The issue of to what extent selection and drift are responsible
> > > > for observed features of organisms is quite subject to
> > > > experimental investigation - the hypothesis that selection is involved
> > > > predicts a lot of convergent evolution - whereas the hypothesis
> > > > that drift
> > > > is involved predicts much greater morphological diversity.
> 
> > > JE:-
> > > The proposition that has to be able to be tested
> > > to refutation is _very_ explicit: Can the process
> > > of random sampling error cause evolution entirely
> > > on its own without selection where evolution is
> > > defined as ANY gene freq. change in a deme?
> > > The short answer is that such a proposition
> > > CANNOT be tested to _refutation_ it can only be
> > > tested to _non_ verification. This means that
> > > all that can be achieved is the elimination
> > > of selection for a significant period of time,
> > > in the experimental way that I have described.
> > > Drift cannot be eliminated unless the experimenters
> > > have an infinite population at their disposal
> > > (which of course they do not). A random gene
> > > freq. change due to random drift must
> > > always exists and cannot _cannot_ be eliminated.
> > > This being the case, all that can be done is
> > > provide an expanding population that is only
> > > subject to random processes (drift mutation
> > > etc). Of course, this experimental population
> > > will always produce a gene freq. change and thus,
> > > according to the definition "evolution".
> 
> > TT:-
> > So you (finally!) admit that sampling errors cause
> > evolution - as it is conventionally defined.
> 
> JE:-
> I don't seem to be getting through...
> 
> I have never denied that the conventional
> definition can cause "evolution" as it defined it.
> What I have repeatedly stated is that such an
> definition only represents an "iron man" theory.
> If you claim that just the random process of sampling
> error can cause evolution without the non random
> process of selection then such a definition of
> evolution becomes _irrefutable_. This means,
> no matter what you do, you cannot refute the
> proposition.

Definitions *are* irrefutable - since they are definitions.

It is scientific theories that are testable.

Evolution as a theory has historically consisted mainly of
the proposition that natural forces are responsible for the
origin and nature of living organisms - and that no designer
or creator was involved.

In particular, Darwin invoked natural selection acting on chance
genetic variation in a population as one of the primary mechanisms 
responsible for generating all living forms.

The *theory* of evolution is *NOT* the hypothesis that gene frequency
changes occur in populations.  Phrased as a hypothesis, that is
blindingly obvious - and hardly needs testing.

> > TT:-
> > All that was ever claimed for the randomness of mutations
> > is that they are random with respect to what is beneficial.
> > They are not "totally" random.  Some parts of the genome
> > are more subject to mutation than others - for example.
> 
> JE:-
> All of statistics exists to define when a
> pattern is random or non random. Either a
> pattern is defined to be random or non random.
> It cannot be claimed that the same pattern
> is random "with respect to what is beneficial"
> but somehow non random with respect to what
> is harmful!

That's not the claim.

Mutations that affect fitness are a subset of all mutations.

It is quite possible for all mutations that arise to consist of a
non-random set - but for there to be no systematic bias favouring
beneficial mutations in that set.

In other words, if you randomly pick a mutation from the set of possible
mutations at any time, it is not especially likely to be beneficial.

Mutations are widely believed to be undirected with respect to fitness.
-- 
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