Jim McGinn  wrote:

> Guy Hoelzer  wrote:
> > in article bh4fp1$rcb$1{at}darwin.ediacara.org, Jim McGinn at
> > jimmcginn{at}yahoo.com wrote on 8/9/03 8:56 PM:
> > 
> > >> I agree in the physical sense.  The language associated
with genetic
> > >> drift as a force is used because drift happens whenever sampling
> > >> happens, so there is the language used is really
intended to indicate
> > >> the association between sampling and fluctuation.  I
think it is more
> > >> accurate to think of sampling and drift as aspects of a single
> > >> process, rather than as a sequential cause and effect.
> > > 
> > > I agree.  In fact this is my main argument for why I
> > > consider the phenomena associated with GD to actually
> > > be part of NS.  I just don't think it was ever
> > > designated/established that NS is a process devoid of
> > > "sample variance."
> > 
> > Darwin and Wallace may have appreciated that "chance"
or sampling variance
> > could have evolutionary effects, but I think that they tried to keep
> > stochasticity apart from the concept of natural selection.
> 
> Darwin explicitly included it.

Using the wonderful resource
http://pages.britishlibrary.net/charles.darwin/texts/> I tracked down
some of Darwin's published comments on chance.

In the "Difficulties of Theory" in the first edition of the Origin he
says:

"To sum up, I believe that species come to be tolerably well-defined
objects, and do not at any one period present an inextricable chaos of
varying and intermediate links: firstly, because new varieties are very
slowly formed, for variation is a very slow process, and natural
selection can do nothing until favourable variations chance to occur
...."

This does not appear in the 6th edition.

I cannot find any other passage of Darwin's on chance that relates to
variation, in a cursory survey.

In the Descent he says in a footnote
"35 I had always perceived ('Origin of Species') that rare and strongly
marked deviations of structure, deserving to be called monstrosities,
could seldom be preserved through natural selection, and that the
preservation of even highly-beneficial variations would depend to a
certain extent on chance. I had also fully appreciated the importance of
mere individual differences, and this led me to insist so strongly on
the importance of that unconscious form of selection by man, which
follows from the preservation of the most valued individuals of each
breed, without any intention on his part to modify the characters of the
breed. But until I read an able article in the 'North British Review'
(March 1867, p. 289, et seq.), which has been of more use to me than any
other Review, I did not see how great the chances were against the
preservation of variations, whether slight or strongly pronounced,
occurring only in single individuals."

This passage puts preservation of fitter variants to chance sometimes.

His son Francis, in a published version of the 1842 essay, notes:

"2The importance of exposure to new conditions for several generations
is insisted on in the Origin, Ed. i. p. 7, also p. 131. In the latter
passage the author guards himself against the assumption that variations
are "due to chance, and speaks of "our ignorance of the cause of each
particular variation. These statements are not always remembered by his
critics. "

Darwin himself says, in the 6th edition, at the head of Chapter V, "Laws
of variation":

"I HAVE hitherto sometimes spoken as if the variations---so common and
multiform with organic beings under domestication, and in a lesser
degree with those under nature---were due to chance. This, of course, is
a wholly incorrect expression, but it serves to acknowledge plainly our
ignorance of the cause of each particular variation."

I think that Darwin did *not* hold that chance was a causal force - he
*did*, however, think that variation was endemic to populations (little
pun).
> 
>   I would be
> > interested in seeing written statements from them to the contrary.  Their
> > overarching goal was to postulate a physical process that caused adaptive
> > evolution.  One thing they did not mention was that stochasticity tends to
> > degrade adaptation
> 
> Not in my opinion.  
> 
>  when the population is reasonably well adapted in the
> > first place.
> 
> Well adapted to what?
> 
>   Stochasticity would have no such bias on an initially random
> > network, and would tend to cause adaptation of an initially
> > worse-than-random network.  Because all organisms and populations of them
> > are enormously better adapted than random networks, stochasticity always
> > tends to degrade biological adaptedness, so its effects run counter to the
> > very condition that Darwin and Wallace set out to explain.
> 
> None of this makes sense to me.  Adaptedness has no meaning except
> with regard to a specified environment.  Environments always have
> stochasticity.
> 
>   I suspect this
> > is still the reason that drift and selection are thought of as independent
> > processes, rather than two complimentary phases of a single evolutionary
> > process.
> 
> IMO, the reasons are psychological.
> 
> Regards,
> 
> Jim


-- 
John Wilkins - wilkins.id.au
[I]magine a puddle waking up one morning and thinking, "...interesting
hole I find myself in - fits me rather neatly, doesn't it? ...
must have been made to have me in it." Douglas Adams, Salmon of Doubt
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