Re: Nando Explains Natural Selection to You!


nando_ronteltap@xxxxxxxxx wrote:
> hersheyh@xxxxxxxxxxx wrote:
> >Syamsu:
> > > It is already teleological that you identify the workings of NS in view
> > > of the result of optimal fitness.
> >
> > Adaptation to local conditions is not teleological because it *never*
> > produces a final optimal end point. For an analogy, think of this
> > year's model of Lexus. It is certainly a good car, but only a fool
> > ignorant of history would think that it is *the* final teleological
> > goal toward which all auto manufacture was aimed. To say that would be
> > to say that, in five years time, there will be no possible better car.
>
> That it not reaches the optimal point is explained by factors outside
> of natural selection, such as chance, neutral selection, genetic drift.
> This leaves natural selection as teleological towards the result of
> optimal fitness.

No. Natural selection is not teleological because there is no *end*
goal in evolution. There are only local conditions to which the
organism adapts. There is no such thing as an *absolute* optimal
fitness which, once reached, means that no further adaption will *ever*
be needed and no further improved fitness is possible. There is only
current *better* [note the use of the comparative -er rather than the
terminal -est] fit to current local conditions. Selection is not about
survival of the fitt*est* (which is absolute), it is about the survival
of the fitt*er* of current forms.

> > > You have to first answer the question why you separate scenario's as
> > > enumerated previously, which are apparently one and the same process,
> > > into separate theories.
> >
> > This is too vaguely stated for me to answer. What "separate scenarios
> > as enumerated previously"? What "one and the same process"?
>
> You want to say X reproduces more then Y is natural selection. But then
> you exclude observations of X reproducing more then Y due to chance,
> neutral selection, or genetic drift from natural selection, eventhough
> we can see it is differential reproductive success. That is the fault
> that Ariew and Matthen point out.

For it to be *selection*, X has to out-reproduce Y because it has a
phenotypic advantage. That is, in any test in the same environment,
phenotype (it is phenotype that the local environments recognize) X
will *statistically significantly* out-reproduce phenotype Y. It may
not do so every time. But over a series of tests, the difference will
be *statistically significant*. OTOH, if X and Y phenotypes are
selectively neutral, such a test will fail to find a *statistically
significant* difference in reproductive success of X over Y (or Y over
X).

But how do you determine if a change is due to neutral genetic drift
(you cannot really have "neutral selection", since neutrality is the
absence of selection) if you cannot repeat the experiment? The answer
is that, *from population size alone*, you can predict mathematically
the odds that a particular observed deviation from no change (from the
'expected' X:Y being 1:1 at birth and 1:1 wrt reproductive success;
i.e., the expectation of neutrality) is likely to be due to chance. If
the deviation from the neutralist expectation is significantly greater
than the amount that can be attributed to chance, then it likely wasn't
due to chance but was due to selection against (selection is always
negative) the phenotype that differentially lost wrt frequency.

> Further you exclude the simple X reproducing more then X', that is the
> environment changes and X reproduces more, and all other kinds of
> similar scenario's where variation is basically irrellevant.

Yes. Because there is no *selection* occurring in these cases. You
cannot have *selection* without variation. What the hell do you think
*differential selection* means?

> You forget
> that adaptation is not a structural property of an organism, but a
> relational property of the organism to the environment.

I haven't forgotten that. But I also haven't forgotten that you cannot
have selection when there is no phenotypic variation so that organisms
can potentially interact relationally with the environment
differentially (in ways that affect and are measured by their
differntial reproductive success).

> Therefore to
> explain adaptation, you would equally need to compare variant
> environments, as you would compare variant organisms.

Why? Adaptation is *to an environment*. An organism can certainly be
better adapted to one environment than to another. And it certainly
can be the case that organisms with phenotype X are better adapted to
environment B than organisms with phenotype Y and that organism Y is
better adapted to environment A than organism X. That is part of what
can drive speciation because you will find (because of their
differential reproductive success) a higher concentration of organisms
with phenotype X in environment B and a higher concentration of
organisms with phenotype Y in environment A. Any change that causes
reproductive isolation will encourage the formation of reproductively
isolated groupings we call species.

> All the possible scenario's, some enumerated previously in the thread,
> are based on the logic that all organisms die, through reproduction the
> forms of organisms are preserved, hence the event of reproduction, to
> reproduce or not to reproduce, shapes the population of organisms.

Well, duh. But it is *differential reproduction of variant phenotypes*
that causes this. Now, I hope I can do this without confusing you, but
selection tends more often to be conservative than resulting in change.
That, of course, is merely a different way of saying that most new
variation tends to fall on the side of being less fit than more fit.
And neutral drift will cause change (but not in features important to
reproductive success in an environment) over time as well. In fact,
most of the evolutionary change we observe (now that we can sequence
DNA) is selectively neutral change. All the *selective* changes that
exist between organisms is an insignificant fraction of the amount of
change due to neutral drift, even though neutral drift is a much slower
process than selection.

> <snip>
>
> > I can't help it that that is how these terms are defined. I certainly
> > object to your misdefining them to mean something else.
>
> Sure you can help it the way terms are defined, by rejecting the
> teleological and biased definitions, and accepting the neutral and
> generally applicable definitions.

I am. You aren't.

> I suggest that evolution comes down to mutation / recombination, and
> what we see after that are changes in populationsize of that mutation.
> It is very clear this way that natural selection is basicly about
> changes in populationsize.

Not if there is no *selection* between variants.

Let me define the terms again.

Evolution means that there have been changes in allele frequencies (and
usually phenotypes, accompanied by speciation). These changes can
either be due to selection or to neutral changes in DNA sequences.
Because neutral changes occur in all organisms even if phenotypically
related change don't, evolution always occurs, even when we see no
phenotypic change.

Selection only occurs when the environment *differentially* and
*significantly* affects the reproductive success of different
phenotypes. Usually, and certainly wrt evolution, we are only
concerned with phenotypes that are due to different genotypes. It is
possible to differentiate between changes due to neutral drift and
changes due to selection, since only the latter is significantly
directional in a constant environment and/or significantly greater than
the expectations of chance alone. Selection, however, tends to be
conservative rather than directional (especially with quantitative
phenotypic traits), working to *prevent* change more often than to
cause it.

Population size changes in the absence of variation or differential
effects on phenotypic variation is NOT natural selection. It is a
measure of the *carrying capacity* of the environment to which the
organism is adapted.


>
> regards,
> Mohammad Nor Syamsu

.

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