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]
> > > > Population structure is not inherited, although allele
> > > > frequency is sampled.  [snip]
> > >
> > > > 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.  [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?
> 
> First, I should clarify that I am using "ESS" in an extended
sense here.
> I am not restricting the term to behavioral social games, in which the
> appropriate level would be the "society" or set of
interacting individuals
> rather than a breeding population.  I am using "ESS" in a more general
> sense of any equilibrium of frequency dependent selection.  Therefore, it
> can apply to any demic level within which reproduction is mostly closed
> and mostly random.

OK. "Deme" is a bit vague any way.
> 
> However, note the problem faced by a species within which different
> populations adopt different ESSs.  Those individuals that live near the
> boundary between the two populations and which paricipate in gene flows
> between the two populations will suffer a decrement to their fitness.  So,
> it is likely that either the two populations will become two species, or
> that one population will "win the election" and impose its
choice of ESS
> upon the other.
> 
> 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.
> 
> > Moreover, a nascent species typically doesn't inherit the mean or mode
> > population structure of its parent. Changes in densities of variant
> > strategies are one of the things that is supposed to drive speciation.
> 
> Yes, but ...  Suppose we have a species which has ESSs stabilized by
> frequency dependent selection on 20 different traits.  That is, we have 20
> independent ESSs being maintained simultaneously.  Then, due to a
> fluctuation, a remote subpopulation deviates from the ESS for one of those
> traits.  The fitness losses due to gene flow drive the erection of
> reproductive barriers and we have a peripatric speciation.  But the child
> species inherits from parent 19 ESS and is "mutant" on one
ESS. Thus, an
> ESS is a heritable species-level trait.  Quod erat demonstratum.

Assuming that ESSs are unlinked, sure. But why assume that the ESSs will
indeed remain as they were? It is vanishingly unlikely that the same
selective regimes will apply to all demes. To assume they *must* we have
to assume some global selection is maintaining them, and that requires
either a uniform selective regime, or some occult force.
> 
> > > Furthermore, although the maintenance of that population structure
> > > takes place using individual-level selection, I don't think that your
> > > parsimony argument applies - the species and its gene frequencies
> > > cannot be removed from the explanatory structure.
> >
> > Why not? If a genus, to use a higher taxon term for argument, consisted
> > of a number of metaspecies, each of which was arrayed geographically in
> > populations similar to their nearest neighbour and with their own
> > population structures, would we need to employ the notion of a species
> > here? Perhaps "population" is the largest necessary
group. So why is
> > "species" a causal player here?
> 
> I'm not sure I understand your question here.  But I think that your
> argument here presumes that I have yielded to your earlier argument that
> an ESS is a population-level entity, rather than a species-level entity.
> But, I did not yield, so I don't need to answer.  I think.  But if I do
> need to respond, please rephrase the question.

I think your argument assumes what it sets out to prove, though. Sorry.
-- 
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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