Guy Hoelzer  wrote:

> in article c79l1c$11cl$1{at}darwin.ediacara.org, John Wilkins at
> john_SPAM{at}wilkins.id.au wrote on 5/4/04 7:54 PM:
> 
> > Guy Hoelzer  wrote:
> > 
> >> in article c7778e$a1v$1{at}darwin.ediacara.org, John Wilkins at
> >> john_SPAM{at}wilkins.id.au wrote on 5/3/04 9:47 PM:
> >> 
> >>> Jim McGinn  wrote:
> >>> 
> >> [snip]
> >> 
> >>>> All traits are species selected traits.
> >>> 
> >>> Even those that are polytypic *within* the species?
> >> 
> >> Perhaps ESPECIALLY those traits that are polytypic *within* the
> >> species.  I think that it is fair to say that selection at one level
> >> tends to coordinate the interactions among the parts that constitute
> >> that level, including the specialization of diverse roles.  For
> >> example, selection at the level of the individual organism seems likely
> >> to have guided the proliferation of tissue, organ, and organ system
> >> diversity within individuals, and engineered functionally effective
> >> paths of interaction among these parts.  I would similarly expect
> >> selection at the species level to engineer within species
> >> polymorphism.
> >> 
> > This is what I don't get about species selection theory. If we moved the
> > level of selection down to the organism, you have just said that
> > intrasomatic genetic variation is maintained by selection upon
> > organisms.
> 
> Maybe it will help you understand the argument for species selection better
> if I clear this up.  I did not say, nor mean to imply, that "intrasomatic
> GENETIC variation is maintained by selection upon organisms."  I referred
> only to the phenotypic variation among the parts of an organism.  I suspect
> this could be effectively modeled using "effective" genomic
differences
> (e.g., including transcriptional differences) among the parts, rather than
> DNA sequence differences.

If I read Lewontin aright, there is no, or little, conceptual difference
between a hereditable trait and a gene for that trait. DNA is a side
issue. We are talking about the frequencies of hereditable differences,
in the organism level case, within a single organism (clearly false;
such variation is maintained by within-organism selection, e.g., by
clonal selection); and in the species level case we are asking if
within-species variation can be due to selection on species. I think it
is false too. Population structure is not inherited, although allele
frequency is sampled.
> 
> > In effect, you are claiming the equivalent or analogue of
> > maintenance of chimerism by selection. How can selection on species
> > cause the maintenance or evolution of intrapsecific variation, and why
> > should we prefer that account to the more likely and efficacious account
> > of selection and drift of individual traits at the organism level?
> 
> The "how" at the species level is answered in exactly the
same way it is
> answered at the individual, or any other, level.  If there is heritable
> variation in form at that level, which is correlated with heritable
> variation in fitness at that level, then selection can get traction.  At

Exactly. And what reason do we think there has been species *selection*?
Species speciate differentially, a kind of sorting process, I grant you
that, but *selection*? That requires hereditability at the level
concerned (which doesn't happen for species, as new species are formed
from demes, and they inherit demic allele ratios, perhaps, sometimes),
and competition (of a population size large enough to overcome
contingency). Selection is a subset of sorting, and not all sorting
processes are selection processes. For example, you can sort pebbles by
water action in a riverbed, but it is not selection.

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.

> both the individual and species levels, genetics provides an
> idiosyncratically constrained but effective path for inheritance.  However,
> it is not the only path available at either level.  The concept of natural
> selection has ALWAYS represented a top-down effect cascade, although our
> devotion to the idea of selection and our reductionistic distrust of

Oh dear - the "r" word. I never fully understood what it was that was
*wrong* about successful reduction.

Yes, selection is a top-down cascade, but only in entities that are
suitably coherent as systems, like organisms.

> top-down influences has generally interfered with our ability to see
> selection in this light.  To put this in Darwinian terms, selection might
> favor a faster cheetah, but it would not distinguish among particular
> mechanisms.  Any mechanism discovered through mutation is favored.  It is
> also important to note that the process of selection requires interaction
> among components of a population that pushes the selective filtering
> process, including selection at the species level.  These are the
"how's."

So far as I can see, here (and elsewhere by others) the argument is an
assertion. If selection at the species level were demonstrated, then it
would be a process of selection that required interaction among
compnents of its populations, by definition. But we are asking how that
might occur at all.
> 
> As to why we should favor the accounting of selection at a level higher than
> the individual, I think we should do so when the optimized outcome of
> selection involves a functional balancing of the interaction structure (a
> network) at a scale higher than the individual.  So, as I just argued in

Fine. I do not think anything has (yet) been so demonstrated, except in
classical group selection cases such as the t-allele case, and these are
not at the level of species. I am unaware of any case that necessitates
a species-level selection process. Of course, this is an argument from
my own ignorance, so I can be (and often am, as Larry sometimes notes)
wrong.

> another post in this thread, I would consider frequency-dependent selection
> to be a circumstance in which top-down effects mold the conditions faced by
> individuals so as to cause selection at the individual level to build an
> optimized structure at the group level.  I see group (e.g., species) level

Group  species. Groups include kin groups, demes, metapopulations, as
well as species. Selection can occur at one level (e.g., the deme, as in
Lewontin's "haystack model") without species being involved. In fact, I
would go so far as to say that the *only* time a species is involved in
group selection is when a species is no bigger than a single deme.

> selection as the dominant mode of selection in this instance, so I think
> that we should favor this level of explanation.  I hope you see how this
> logic can be extended to other circumstances.  I would also add the caveat
> that processes other than selection (e.g., mechanisms of self-organization)
> can also lead to top-down effects.

That goes without saying.
> 
> > What selection on organisms does is not to maintain intraspecific
> > variation of *genes* except the production of immunological antibodies
> > (which are not preselected), and every cell in that body shares the same
> > genome, suitably expressed or repressed, at some point in the
> > proliferation and potentiation of itself or its precursors.
> 
> I hope I cleared up this issue above.
> 
> > This overall developmental cycle is maintained by selection on organisms
> > according to the properties of these traits.
> 
> I agree that selection at the individual level (and lots of self-organizing
> processes within the developing individual) is the primary design influence
> on patterns of individual development.
> 
> > But there is nothing
> > analogous in species selection. There are no developmental cycles in a
> > species.
> 
> Well, lots of folks would disagree with you here.  Take, for example, the
> Carson/Templeton model of genetic transilience.  This is an example of a
> model of speciation that predicts a developmental trajectory for species.
> Stan Salthe's publications on hierarchy theory also argues that all
> dynamical systems, including species, go through the same generic form of
> development (immaturity, maturity, senescence).  Plenty of
> macroevolutionists have similarly considered developmental pathways for
> species.

The founder flush model is one of population dynamics, and is not, so
far as I know, programmed, but falls out as the effects of each
particular founder population. Transilience (as I imperfectly understand
it) is a process within a *population*, involving inbreeding.
> 
> > Population structure is largely contingent - there is no
> > mechanism for dividing demes, or structuring them, or modifying that
> > structure, apart from individual selection and drift, or in short
> > ordinary population genetics.
> 
> My work, and that of others like Yaneer Bar-Yam, is showing otherwise,
> although we are focusing on the spatial self-organization of population
> structure.  Again, macroevolutionists like Dave Jablonski have been writing
> for years about the evolution of mechanisms that divide deems (e.g., direct
> vs. plantotrophic development in marine gastropods).
> 
> > So how is the downward arrow of causation applicable in this case? In a
> > homeostatic system like an organism, the state of the system can affect
> > the satte of the parts, but species are barely if at all homeostatic,
> > gene flow accounts (which apply at the individual level)
> > notwithstanding.
> 
> You are right to point to homeostasis.  I would argue that in species, like
> in individuals, homeostasis happens.  I would also argue that it is a
> tenuous state at both levels, and it may well be that individuals are
> generally more homeostatic than species, at least at this point in the
> history of the biosphere.  However, I see this as a difference of degree,
> rather than of kind (sorry JE).
> 
> > I would appreciate your views on this Guy. Larry Moran has tried to
> > explain it to me, but I just don't "get" it. And I am
afraid I find
> > Gould's views incoherent.
> 
> Me too.
> 
Thanks for the attempt, Guy. I am afraid that I still think species
selection is either a fallacy of composition, or a fallacy of division,
depending on how the argument is framed. It matters where the properties
are located, and they are not located at the species level.

Of course, you have one very big advantage over me - you are a working
scientist, and I am an armchair philosopher. But occasionally philosophy
mentions some unpleasant truths; perhaps it may be this time.

-- 
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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