Re: 50% mutation
From: Perplexed in Peoria (jimmenegay_at_sbcglobal.net)
Date: 02/21/05
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Date: Mon, 21 Feb 2005 00:48:40 -0500 (EST)
"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.
> 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.
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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