Re: 50% mutation
From: A.C.H. (br.hessels_at_planet.nl)
Date: 02/22/05
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Date: Tue, 22 Feb 2005 01:25:13 -0500 (EST)
"Perplexed in Peoria" <jimmenegay@sbcglobal.net> wrote in message news:<cvbsno$14ie$1@darwin.ediacara.org>...
> "A.C.H." <br.hessels@planet.nl> wrote in message news:cvb06a$rhm$1@darwin.ediacara.org...
> > A lot of evolution is the result of quantitive changes. In human
> > evolution, for example, more brain, less hair, less snout etc. etc.
> >
> > These changes are the result of changes in the regulation of genes;
> > how much, when and where a certain gene-product is produced. (And not
> > of changes in the gene-products themselves.)
>
> Actually, some aspects of regulation involve gene products (i.e.
> proteins). In fact, many aspects do. But I get your point.
i confess almost total ignorance on this point.
>
> > The thing i want to point out is that the variables more-less,
> > earlier-later are one-dimensional. A mutation in a regulatory sequence
> > results in a phenotypic change along one dimension.
> >
> > Now consider a situation of directional selection, a situation where
> > some adaptive change is required.
> >
> > The chance of a favorable mutation, a mutation with with positive
> > fitness, is exactly 50%. (since either more or less, earlier or later
> > necessarily results in positive fitness.)
> >
> > Am i missing something?
>
> Well, one thing you may be missing is that too much hair (for example)
> is bad, but so is too little hair. If the species is already at the
> point where it has just the right amount of hair, then any mutation
> is bad.]
That's why i was stressing directional selection.
> So how can a species with just the right amount of hair continue to
> evolve? It can't! At least not along the amount-of hair dimension.
> But that doesn't stop mutation from trying to fiddle with hair.
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