Perplexed in Peoria  wrote:

> "John Wilkins"  wrote in message
> news:c7ph34$1gh$1{at}darwin.ediacara.org...
> > Perplexed in Peoria  wrote:
> >
> > > "John Wilkins" 
wrote in message
> > > news:c7mqjd$262r$1{at}darwin.ediacara.org...
> > > > Perplexed in Peoria  wrote:
> > > >
> > > > > "John Wilkins"
 wrote in message
> > > > > news:c7hmdm$i0l$1{at}darwin.ediacara.org...
> > > > > [snip much]
> > > > > > As Eldredge noted, species do not
"moremake" in the requisite
> > > > > > manner to be subject to selection. They
split, bud and become
> > > > > > disrupted, but at the species level their
properties are not
> > > > > > inherited. The principle of parsimony
suggests that if we can
> > > > > > account for what happens in terms of a
lower-level process
> > > > > > (i.e., a population genetic process) then the
higher level
> > > > > > explanation is otiose. [snip remainder]
> > > > >
> > > > > I believe that your arguments don't apply to the kind of
> > > > > species-selection that I describe in my latest
response to Guy.
> > > > > Population structure can be heritable if that
structure is an ESS.
> > > > > Fluctuations from that stable structure are repaired.
> > > >
> > > > Subtle. But is an ESS a species-level property or a
population-level
> > > > property? By this I mean, is it a property that must be
borne by the
> > > > entire species rather than by parts of it - is it an ESS in a
> > > > population because the boundary conditions of that
population form
> > > > that trade-off to be stable, or is it something that
must apply to
> > > > entire species?
> > >
> > > The ESS doesn't *have to* apply to the whole species, but by the
> > > definition of a biological species, it usually will.
> >
> > I'm not sure about this. An ESS is, by definition, local to a deme and
> > its exigencies. If a population exists in a slightly (or greatly)
> > different selective regime (= environment), it may maintain a different
> > ESS using the same alleles - all that is happening then (WRT the alleles
> > in question) is that there is a flow of genes between populations, each
> > of which will settle into an ESS (or not, depending on the dynamics, but
> > assume they do).
> >
> > Hence, it does not follow that we must treat a multidemic biospecies as
> > a single deme with a species-wide ESS.
> 
> Hmmm.  I think that I am just now beginning to understand your argument.

I am opaque. I'm sorry. I try to express these things that seem so clear
to me, but as so many folk have trouble I must not be doing a good job.

> Let me know if I paraphrase it correctly.  "Even though a trait may be a
> species-level trait, in that there is no variation for that trait within
> the species, Jim's proposed mechanism of species-level selection for that
> trait would also work as a mechanism of population-level (or group-level)
> selection if the species did vary for that trait.  Group-level selection
> is still group-level selection, even if the group in question is the
> entire species. Therefore, we don't need the concept of species-level
> selection."

Sort of. It is not that a trait *does* vary within species, but that it
*can*, and if it does then it can go to fixation (i.e., spread to the
entire species) through population-level dynamics. If that is true then
there is not a presumption that because something is species wide - an
invariant character - it had to have occurred through dynamics at the
species level (barring mutations, all my cells that have a genome have
the same genome, and this is not due to selection against genetic
chimeras in the past; for some individuals are chimeras).
> 
> If that is what you are saying (approximately), then all I can do is to
> point out (again) that the species level is special in that there are no
> disruptive gene flows to disrupt the frequency- dependent equilibrium
> which I take to be crucial to a polymorphism being heritable.  But, since
> you have heard that before, I suppose we will just have to agree to
> disagree.  Unless, that is, I have completely misinterpreted your
> position.

Some species are cohesive gene pools. Many are not. It follows that the
category "species" itself is not definable in terms of cohesive gene
flows. Hence the idea that a species exists because there has been some
selection for species-wide traits in the past is less secure; you still
need to show that enough species are cohesive. I don't think that the
evidence supports this.

Perhaps I had better say what I think species *are* then. In my view, a
species is an effect, not a cause. It is real enough, and in the case of
sexual species reproductive isolation keeps it real (and novel isolation
makes more species), but isolation is a property of a relation between
two breeding individuals, and additively of populations. Hence, unless
the individual effect here (groups isolated by various mechanisms)
results in a suitably cohesive entity (which it mostly doesn't) species
cannot act as "players" in any process that cannot be eliminated in
favour of a more causal story at a lower level.

I do not deny that [some] species *may* be subjected to a selection
process at that level. I merely deny that anyone has given good reason
yet to show they have. The problem is threefold:

1. To show that species are cohesive enough to "act" as an individual
(the precondition for entering into a selection process);

2. To show that those that are have, in fact, properties of a causal
nature at that level (the precondition for *actually* entering into a
selection process); and

3. To show that enough of these beefed up species interact in ways that
causes a selection process to result (showing that they *do* enter into
a selection process).

I will grant 1 and 2 in some isolated cases - although so far they are
all at the demic level. But I haven't seen reason to think that 3
obtains or that there is even an epistemic advantage to think it might
obtain/
> 
> The only other possibility seems to be that you are disputing, as a matter
> of fact, that there exist any species-level frequency dependent equilibria
> that are stable in the sense that any sub-population that switched to a
> different equilibrium would either be forced back to the global
> equilibrium by gene flow or would be induced to erect reproductive
> barriers.  And I can't believe that you would adopt that position of fact.

No, that is to the side of my claims in this argument. It merely
supports point 1.
-- 
Dr John S. Wilkins, www.wilkins.id.au
"I never meet anyone who is not perplexed what to do with their
 children" --Charles Darwin to Syms Covington, February 22, 1857
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