"Guy Hoelzer"  wrote in message
news:c7ph2v$17v$1{at}darwin.ediacara.org...
> in article c7jqhu$199a$1{at}darwin.ediacara.org, Perplexed in Peoria at
> jimmenegay{at}sbcglobal.net wrote on 5/8/04 4:30 PM:
>
> [species selection and polymorphism as a species trait]

> > A good heuristic for identifying candidate instances of something that
> > is maintained by species-level selection is that the same pattern of
> > polymorphism exists in all species of a higher-level taxon.  (We don't
> > assume individual level selection everytime we notice a single
> > individual with some adaptation, but we do suspect selection if that
> > adaptation is prevalent among all individuals in the species.)
> >
> > Therefore, I believe that the following are probably due to
species-level
> > selection:
> > 1. Sexual reproduction, which is maladaptive for female individuals.
> > 2. Caste polymorphisms, including sterile castes, in social insects.
> > 3. The system of A, B, AB, O blood types - which exists in primates
> > generally.  I am assuming that most primate species whose founders
> > lacked either A or B alleles suffered extinction due to disease.
>
> It's my turn to play devil's advocate.  What, besides their being
widespread
> in certain taxonomic lineages, makes you think that these cases represent
> examples of species selection, rather than some process of
self-organization
> that did not involved differential reproduction or extinction among
species?

First, let me point out that I am claiming that these species-level traits
are *maintained* by selection, not that they arise by selection.  By
comparison to neo-Darwinian individual-level selection, individual-level
traits arise by mutation - they are only fixed and maintained by
selection.  Species-level traits arise either by inheritance at
species-birth, or by processes analogous to individual-level mutation -
namely environmental fluctuations and finite sampling effects in small
populations.

Second, let me complain about the term "self-organization" that is being
offered as a conceivable alternative to selection.  I don't know what this
term means in the current context - population genetics.  I can imaging a
process of spatial structure creation analogous to Turing or Brusselator
dynamics in chemical thermodynamics.  But I don't see what this has to
do with the current question.  I'm talking about species-level traits here -
there is no spatial structure.

So I'm going to try to answer a slightly different question here.  If this
is
not what you are looking for, then ask your question again in different
terms.

The question is - "If you want to call this selection, then you must
show that there are alternatives to be selected against.  (In the
individual-level analogy, these would be alternative alleles.)
Furthermore, you must show that mutation is possible from the
selectively favored alternative to the less favored one.  (After all,
this is the situation that your "selection" is claimed to counteract.)
Finally, you must show that it is selection, rather than some kind of
"mutation pressure" that leads to the current situation.  (In the
analogy with neo-Darwinism, there is mutation from the wild type to a
recessive allele more frequently than in the reverse direction.  This is a
kind of mutation pressure, understandable in terms of informational
entropy, that selection successfully overcomes.)"  That is the question
that I will address.

The easiest one to cover is #3 - the polymorphism of A, B, AB, and O
blood types.  An alternative would be the loss of the B allele from the
species population, mutating this polymorphism to simply A and O.  Such
a mutation is clearly possible - either at species birth or in an existing
species if the population size is low.  Also, it is clear (or at least
plausible)
in this case that the mutation pressure is likely to be toward loss of the
B allele, rather than in the appearance of the allele de novo in a species
that lacks it.  Finally, I have provided a hypothetical mechanism of
selection - a mutant species, lacking the B allele, may be more
vulnerable to extinction from infectuous diseases.

Next, #2 - caste structures in isoptera and hymenoptera.  Obviously
alternatives exist and mutation is possible - we see different caste
structures in different species.  To discuss mutation pressure, I need to
have a pop gen model.  So I am going to focus on the only aspect of
this that I know anything about (thanks to Bill Hunt) - effective sterility
of workers induced by the destruction of worker-laid unfertilized eggs
by other workers.  Obviously, there is frequency-dependent selection
involved here involving at least three loci affecting behaviors of both
queens and workers.  And, by my reading of the distribution of this
behavior in Melopena and Apis, mutations have occurred in both directions.

Finally, proving that this is species-level selection rather than
colony-level
selection requires only that the frequency-dependent equilibria upon
which this entire explanation depends would be disrupted if neighboring
colonies used different strategies.  That is, colonies that sterilize their
workers by larval diet cannot successfully interbreed with colonies
that sterilize by egg destruction, and neither can interbreed with colonies
that permit workers to father drones and use genetic mechanisms to
determine the queens.

Of course, it could be argued (by Wilkins, for example), that I have only
shown population-level selection here, not necessarily species-level.
Ultimately, that distinction may best be made by asking whether different
populations within a species do actually exist with different values for
what I want to call species-level traits.  If variation within the species
does exist, then I would have to concede that the trait is not really a
species-level trait.

Finally, #1, the maintenance of sex.  This subject is too large for this
reply -
in fact, it is too large for a monograph.  And I don't really know that much
about it.  So I will limit myself to dealing with only one aspect of the
issue - the sexually reproducing desert reptile genera that occasionally
give
rise to parthenogenetic subspecies.  Except, here I think that the
definition
of the biological species concept requires that these parthenogenetic
populations be called species in their own right.  Is there species-level
selection involved?  I can only point the reader to the graphs on p203
of the Canto edition of Maynard Smith's "The Theory of Evolution".
(I am sure you have seen graphs like these before - comparing the
time series of the population of the sexual and parthenogenetic
portions of the composite population.  They appear in every textbook.)

Guy, if this has not addressed your question, ask again.  Follow-up
questions are welcome.
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