Guy Hoelzer  wrote:

> Hi John,
> 
> in article c92cvt$3s4$1{at}darwin.ediacara.org, John Wilkins at
> john_SPAM{at}wilkins.id.au wrote on 5/26/04 8:26 AM:
> 
> > Guy Hoelzer  wrote:
> > 
> >> in article c8aldf$18ru$1{at}darwin.ediacara.org, John Wilkins at
> >> john_SPAM{at}wilkins.id.au wrote on 5/17/04 8:23 AM:
> >> 
> >>>>> GH:
> >>>>>> I can imagine ways that it could be
programmed into species, although I
> >>>>>> don't know of any examples.
> >>>> JM:
> > JW...
> >>>>> Please give...
> >>> GH:
> >>>> Some kinds of dispersal processes increase the chance
of colonizations
> >>>> followed by long periods of genetic isolation.  A
classic comparison is
> >>>> between Hawaiian Drosophila and say Hawaiian
crickets.  It is clear in
> >>>> this contrast that dispersal mechanisms are heritable
(programmed) at
> >>>> the species level, and that this difference has
resulted in a greater
> >>>> rate of founder/flush events among the Drosophila
than among the
> >>>> crickets.
> >> JM:
> > JW...
> >>> How is dispersal programmed at the species level? If
there is something
> >>> about the *species* rather than the behavioral programs of the
> >>> individuals that causes dispersion, and this is hereditable, then I
> >>> would agree, but dispersion is a fucntion of the
individual behaviors of
> >>> the organisms, and the geography in which they find themselves.
> >> 
> >> First I want to reiterate a point about my view on multilevel
selection so
> >> that my response does not leave a false impression.  I do not see any
> >> reason to limit the mechanisms of adaptive response to selection at any
> >> particular level to modes of interaction among the parts at that level.
> >> For example, I see no reason to disallow mechanisms of
inheritance at the
> >> individual level (e.g., genetics) to function also as mechanisms of
> >> inheritance at the group level because nature is not so
restricted.  So,
> >> in my view, genetic influence over the dispersal behavior of
individuals
> >> can also provide a mechanism of heritability at the species
level, which
> >> can give traction to selection pressure at the level of the species.
> > 
> > Yes indeed. The mechanisms of heredity at the genetic level can be the
> > efficient cause of heredity of properties:
> > 
> > - at the organ or tissue or internal anatomical level
> > - at the organism trait level
> > - at the kin group level
> > - at the deme level
> > and even (draw breath and hold it)
> > - at the species level.
> > 
> > (Release that breath now)
> 
> Done.  Thanks.
> 
> > The question, though, is whether the properties inherited are unique to,
> > and causally relevant at, each level. If a species has the property of
> > being composed, for example, of panmictic populations because
> > individuals range across the entire range randomly, then the selection
> > that is going on is selection, at best, between demes.
> 
> I agree that deme structured systems lend themselves to group selection, but
> I don't see why selection cannot work at the individual level within a
> panmictic group.  Panmixia was assumed in most of Fisher's models of natural
> selection, for example.

Sorry, I was setting a maximum level here, not a baseline or a minimum.
> 
> > The species is
> > composed of these demes, and inherits the
"deme-property". It is not
> > therefore species selection if a species is ecologically supplanted by a
> > more panmictic species, unless what is inherited is at the level of
> > species, and only at the level of species, rather than being complete,
> > as it were, at the lower demic level. An organism with a trait that is
> > fitter than another trait of another organism has that trait because of
> > the gene-level heredity (plus the often-overlooked developmental
> > machinery) but the trait is an organism-level trait. The selection
> > occurs at that level. So-called "selfish DNA" is
selected at the genetic
> > level, and so on.
> 
> This is the approach commonly used for the pedagogical purpose of generating
> an understanding of how selection at levels other than the individual can
> operate.  However, IMHO there is no need to limit the concept of multilevel
> selection in this way.  For example, why would it be impossible for a
> mutation to occur that provides benefits to individuals in competition with
> other individuals AND also provides benefits to the whole species as it
> competes with other species?  If this is indeed possible, then copies of
> this mutation will tend to proliferate under the positive influence of
> selection at both levels.  At the same time, selection at other levels may
> contribute suppressing influences on frequency change of the mutation.  In
> sum, I don't see any reason for us to peg a single level at which selection
> influences the fate of any particular heritable change in information, if
> that change is heritable and affects phenotype at more than one level.

It is possible. I'm really only making a philosophical point here - that
the ascription of properties to entities has to be at the relevant
causal level. For instance, I could say, if I were of a mind to, that
Earth is intelligent, because aspects of Earth are intelligent, but it
is merely a metaphor, and can cause confusion, which is, I think, at the
heart of the debate over species selection and macroevolutionary
processes. If the *Earth* were intelligent, then *it*, and not just a
small carbon-based unit component of it, would be able to intelligently
respond to stimuli.

At some point this has no theoretical implications - if you have a model
in which taxa reliably "inherit" properties as a result of within-taxa
processes, and you can show that this has an effect on the differential
persistence of those taxa, then all we are arguing over is the meanings
of words. My major problem is the ambiguity in using the same terms
(inherit, selection, progeny, fitness) for both levels and sliding from
one to the other, often unconsciously. 

As we have seen in this thread, some people are vehement in their
intuitions that what applies at one level must apply at other levels
[ask me about the Platonic macrocosm/micrcosm distinction sometime, and
what confusion *that* caused in science]. I think this is why many
people make overblown claims about the need for group selection to
account for things that are accountable in lower level terms.
> 
> >> That said, I can also speculate on mechanisms of
"programming"
> >> dispersal patterns at the species level that are not fully encoded by
> >> the genetics of individuals.  Imagine, for example, that the
> >> genetically encoded tendency to disperse is contingent on the degree of
> >> social crowding (e.g., intraspecific competition) or the inability to
> >> find a sufficiently well coordinated social group to join.  Then the
> >> actual dispersal patterns observed at the species level could reflect
> >> an emergent interaction of properties at various genetic loci affecting
> >> contingent dispersal rules, rules of social and ecological interaction,
> >> and the external environmental context in which the population finds
> >> itself.  In this situation, it would be possible for the realized
> >> dispersal behavior at the species level to be effectively programmed
> >> and quite independent of the dispersal rules programmed at the
> >> individual level.
> > 
> > I have already delivered myself of my dismissal of emergence as a
> > metaphysically interesting feature of physical systems, so I won't
> > rehearse it here. Flocking behavior, though, is a property of individual
> > birds (or boids) and their genetic and developmental programs, not of
> > flocks...
> 
> I'm afraid that I don't understand your objection to my example.  I agree
> that flocking behavior is a property of individual birds, and not of flocks.
> Similarly, flocks are a property of a species, not of individual birds.

Flocks are an entity. They are a "property" of themselves. They are
components of demes, and thus of species. Again, the part-whole
confusion and the compositional fallacy.

> Therefore, a single genetic mutation can lead to heritability of flocking
> behavior at the individual level, and flocks at the species level; so
> changes in the frequency of this mutation can potentially be influenced by
> selection at both the individual and species levels.  Do you agree?

That would be too easy. Of course not, and yet, I do, sort of. Hope that
clears it up.

-- 
John S Wilkins PhD - www.wilkins.id.au
  a little emptier, a little spent
  as always by that quiver in the self,
  subjugated, yes, and obedient.  -- Seamus Heaney
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