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)

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. 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.
> 
> 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...

-- 
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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