Re: No distinction between artificial and natural selection - John

r norman <r_s_norman@xxxxxxxxxxxx> wrote:

On Sat, 05 Apr 2008 03:01:20 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:

r norman wrote:

On Fri, 04 Apr 2008 02:36:19 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:

r norman wrote:

On Thu, 03 Apr 2008 02:12:05 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:

<major snippage to leave just the following point>

I do think that it would be helpful to come up with a
usage that differentiates "evolution" and "natural selection", and that
such a usage should recognize that all sorts of processes, including
mutational bias, can impart a direction to evolution.

I don't know why it should be necessary because natural selection is
not the same as evolution and certainly has not been for a half
century, since the 'modern synthesis.' Natural selection is one of
the mechanisms by which evolutionary change occurs, but only one of
several. Anybody who has ever taken a decent college intro biology
course should know that.

However I don't see how 'mutational bias' impart a direction to
evolution unless the mutations are themselves directed. It is well
known that selection is the dominant, if not the only, directed
mechanism.

Arlin Stoltzfus says otherwise, at least with regard to "the only" part -
he is rather scornful of the 'modern synthesis' claim that the gene pool
invariably has sufficient variability that mutation rate and bias is not a
factor in evolution. But you had better argue with him, because I don't
know enough about the subject.

As to your first argument, evolution and natural selection are often used
interchangeably in popular usage. While I am not holding my breath, I
would advocate for the replacement of "natural selection" with some other
term that captures what Dawkins called "The Blind Watchmaker". That is of
course
exactly what was originally intended by the term "natural selection", but
usage changes. I can remember when "retarded" was a euphemism, instead of
a pejorative - in fact I think it was my generation that effected the
change :-)

I never would claim that mutation is not an important factor in
evolution. I only questioned the notion that it is a 'directed'
factor. The evolutionary mechanisms beyond selection include
migration, mutation, and drift. Migration, or more properly gene
flow, might be considered a directed factor if were really restricted
to voluntary migration by animals with very specific phenotypes to
allow them to make the trip and determine where to settle. However,
much of gene flow is spores, seeds, and pollen blowing in the wind or
organisms blown out to sea on some sort of raft or carrying on birds
feet, etc. These flows are not really dependent on the genotype or
phenotype of the migrant and so could not be considered directed.
Drift, by definition, is not directed.

Thanks for reminding me about migration - I generally forget it as an
influence in evolution, even though I should know better. You did not
mention founder effect, which Mayr, for one, seems to think is important.
Perhaps you are including it with drift because the mechanism is similar,
but I think it worthwhile to differentiate because of the one-time nature
of founder effect. As Carroll has pointed out, even if drift eliminates a
possibly beneficial mutation, it will be continually reintroduced, and over
time is very likely to be fixed. Founder effect can more readily freeze an
accident, and thereby introduce more stochasticity (if that is a word) to
evolution.

So please explain to me why
you call mutation a directed factor.

As I tried to explain above, I don't call mutation a directed factor, but
Arlin Stoltzfus, whom I know to be knowledgeable on the subject, does. He
explains the reasons in a paper which I could e-mail to you, but perhaps
I or you should get his permission, as it is copyrighted. The gist of his
argument is that the gene pool does not always provide sufficient variation
for natural selection to function independently of mutation rate and
mutation direction, contrary to the claims of the Modern Synthesis.

As to the conflation of natural selection with evolution, perhaps some
people still live in total awe and worship of Darwin, as far too many
creationists believe. However biology has passed through a
'nonDarwinian' evolution phase whose ideas are now so thoroughly
accepted that nobody even bothers to refer to these other mechanisms
as nonDarwinian and haven't for more than a quarter or third of a
century, now. Rather than change a well ensconced term, why not just
educate the public?


I was going to use the term "conflation" and was scared away after a
webcheck indicated the usage might be more akin to combining terms than
confusing terms. But a further check after seeing you use it makes me think
it is the right term after all. As to educating the public, what kind of
crazy talk is that?

More seriously, as I tried to point out with my reference to "retarded",
there are times when terms should be jettisoned because they no longer mean
what they were intended to mean. People look at nature and they see design,
because it is there. Darwin explained this as natural selection by analogy
with artificial selection - breeding producing design, whether the breeding
is intentional by humans or dispassionate by the environment. If we can
reinvigorate the term natural selection as a powerful design force rather
than a random walk, well and good. I think it helps in arguing against
intelligent design to demonstrate the efficacy of evolutionary design.


About the founder effect: it certainly is important, but is better
considered a combination of several mechanisms at work. First, there
is migration of a small portion of an existing population to a new
area. That involves a form of drift because the small sample of
founders does not represent the full spectrum of genetic variability
in the parent population. It involves traditional drift, too, as the
founder group in the new environment is a small population. Finally,
it involves selection as the population in the new environment is
usually subject to radically different environmental selection
pressures than the parent group. I believe the idea is that the
mechanisms of evolution are fundamental, elemental pieces. Real life
always involves a combination of these acting simultaneously and is
best explained in that way instead of multiplying fundamental factors.
By the same token, catastrophic extinction events are a very
important factor in evolution, but really just represent a drastic
alteration in the environment and fall under the rubric of selection,
a rather extreme selection, but selection nonetheless. Alterations in
the environment are not normally considered mechanisms of evolution.
They are simply a part and parcel of the real world that biological
organisms must cope with and respond to evolutionarily, that is, using
the evolutionary mechanisms available.

The only work of Stoltzfus I can see that deals with directional
selection is the paper "Mutation-biased adaptation in a protein NK
model" in Mol Biol Evol. 2006 Oct;23(10):1852-62. In the abstract, he
writes: "A possibility that has been ignored, presumably because it is
part of neither the Modern Synthesis nor the Neutral Theory, is that
mutation may impose a directional bias on adaptation. " Here he seems
to be talking about things like GC:AT bias in nucleotides producing a
bias in amino acids, hence a "directed" evolution. The directional
change does not seem at all to be related to fitness or adaptation but
could be considered 'directed' in a very technical sense.

Finally, about the main subject, you say: "If we can
reinvigorate the term natural selection as a powerful design force
rather than a random walk..." Whoever claimed that selection is a
random walk? That metaphor (analogy?) is exactly what is claimed for
drift and for mutation (at least the non-directed evolution which not
even Stoltzfus denies). The whole point of selection, its enormous
importance, is exactly the point that it is NOT a random walk but
specifically produces adaptation exactly in the way Darwin described.
The nonDarwinian evolution argument points out that this is not the
only thing that is important but it certainly does not argue that
adaptation through selection is insignificant!

A philosophical nicety: bias <> directed. There can be biases in the
likelihoods of mutations, without the mutations having a direction to
some fitness enhancement. Even under Arlin's approach, there is no
direction, just a [chemical] tendency to have certain kinds of mutations
occur more often.
--
John S. Wilkins, Postdoctoral Research Fellow, Philosophy
University of Queensland - Blog: scienceblogs.com/evolvingthoughts
"He used... sarcasm. He knew all the tricks, dramatic irony, metaphor,
bathos, puns, parody, litotes and... satire. He was vicious."

.

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