Text 868, 97 rader
Skriven 2004-11-19 06:15:00 av Perplexed In Peoria (1:278/230)
Ärende: Re: The "fuel" of evoluti
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"phillip smith" <deletethis-phills@ihug.co.nz> wrote in message
news:cniip7$2676$1@darwin.ediacara.org...
> in article cnhhln$1rrr$1@darwin.ediacara.org, Perplexed in Peoria at
> jimmenegay@sbcglobal.net wrote on 18/11/04 8:06 PM:
>
> > We all know that heritable variation in characters affecting fitness
> > is a prerequisite for natural selection.  Metaphorically speaking,
> > we can even say that heritable variation is the "driving force"
> > for NS.
> >
> > This is a good metaphor because variation plays a force-like role.
> > Assuming you quantify "variation" as the variance in fitness, the
> > infamous "Fisher's Fundamental Theorem" assures us that the
> > magnitude of the response is proportional to the magnitude of the
> > "force".  Furthermore - (correct me if I am wrong here!) - the
> > direction of the response matches the direction of the "force".
> > If the total variance in fitness is divided among several
> > characters, the characters that evolve fastest are those that make
> > the largest contribution to the fitness variance.
>
> I think you may be in error here. Standard darwinism is not directed by
> variation, assuming variation is every direction. Heritable variation in
> characters does not force evolution. The rate of evolution is proportional
> to variation. The force is the strength of selection. You could have very
> high variation and no change at all in under intense stabilising selection.

I may well be in error, but your response suggests that I was simply not
precise enough.  My claim is (ie. was meant to be) that the total "force"
is the total variance in fitness attributable to heritable variation in
characters, with the various orthogonal components of that total being the
heritable variation in fitness due to each character.  My understanding -
again, please correct me - if that under stabilizing selection the variation
in fitness due to a character is simply not heritable.

I do notice one difference between a real force vector and a variance
"vector", which is that the variance components are always positive.  The
response vector, on the other hand, is truly vector-like.  That may be
enough to destroy the metaphor.

> However Kimura and Ohta had other ideas. If you take evolution as the change
> in gene frequecies then the rate of evolution is a function of the mutation
> rate ie variation if accept the neutral theory.

Oh, I do subscribe to the neutral theory.  Again I was probably insufficiently
precise.  If I said that my "force" was driving "evolution", then I was wrong.
I should have said that the "force" drives "adaptation" or drives "natural
selection".

> It is a bit like diffusion vs mass flow.

You lost me here!  Is Fisher like diffusion and Kimura like mass flow, or
vise versa?
>
> Snip
> > Of course, the true value of a metaphor lies in the follow-up
> > questions that it suggests.  Is there a difference in the fuel
> > efficiency of various evolutionary situations?  Does the combustion
> > require two different fuel components (oxidizer and reductant)
> > with either component potentially limiting?  Etc.
> >
> >
> I think a trap you may be falling into here is believing that fitness is a
> real property of individuals. Fitness can only be ascribed to alleles.

Actually, I'm pretty sure I was claiming that total fitness is modeled as
a property of types, with the components of fitness being modeled as
properties of alleles.

> We can measure the frequency of an allele at time x and x +1 and see a change
> frequencies and try and determine the probability the change happening by
> chance. If chance seems unlikely then maybe it was selection.
> Fitness is a very slippery concept ...

Gee.  I didn't realize that.  John and I seem to have no trouble understanding
each other re "fitness".  ;-)

> ... and I personally feel it has been badly
> formulated. I am working on an alternative formulation that I feel is
> superior but requires a rethink of population genetics. Unfortunately I need
> to publish first in scientific journals for all the reasons that have been
> recently discussed so I can not reveal it to sbe. This has been the fruit of
> some ten years work. I need to finish the phd I should have finished eight
> years ago. I have recently returned to a lab part time about 8 hours a week
> when I am not  working. So I hope to finish this soon. I look forward to
> presenting my ideas to sbe at the appropriate time.

Sounds interesting.  I look forward to it.
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