Perplexed in Peoria  wrote or quoted:
> 
> "Tim Tyler"  wrote in message
news:cds2f5$1r9i$1{at}darwin.ediacara.org...
> > Jim Menegay  wrote or quoted:
> > > Tim Tyler  wrote in message
news:...
> > > > Perplexed in Peoria 
wrote or quoted:

> > > > > The correct lesson to take from the "new
group selection"
> > > > > is that groups have a role ONLY IF they are
ephemeral and if the
> > > > > organisms in those groups do most of their
breeding outside the
> > > > > group.
> >
> > > > I don't think I've even heard of some sort of "new
group selection"
> > > > that depends for its existence on outbreeding.  What is all that
> > > > about?
> > >
> > > Basically, I was referring to forms of "group
selection" based on the
> > > Price equations and on D. S. Wilson's "trait group
selection".  These
> > > forms of "group selection" do not seem to conform
to Ridley's
> > > definition, though they do involve selection acting on (or through)
> > > groups.
> >
> > I still can't see how your original capitilised section applies - i.e.
> > how outbreeding and groups being ephemeral help with Wilson's flavour
> > of group selection.
> 
> Well, outbreeding and ephemeral groups are part of the _definition_ of trait
> group selection.  As to how they help, read Wilson.  Also, my last few
> paragraphs below.

Hmm.

Wilson's argument appears to boil down to observing that there's a
possibilty that traits which cause reduced individual reproductive
success within a group can spread - if groups consisiting of individuals 
with those traits are more successful than groups of individuals without 
them.

Outbreeding and loose group boundaries don't destroy the idea -
but they hardly seem like an essential part of it to me.

In the case where the groups are totally disjoint, the idea
still seems to apply in just the same way.

> > > However, I may be missing some subtlety here.  I have still
not read the
> > > papers of Queller, Wilson et al, and Taylor that are referenced by
> > > Hamilton and Perrin.  So, if someone has read those papers, and can
> > > correct my misunderstanding, I would appreciate it.
> >
> > Group selection - AKA differential reproductive success of groups
> > of organisms - depends on variation between groups.  I'm hard pressed
> > to think how outbreeding is going to help it.  Outbreeding tends to
> > destroy variation between groups, and acts to remove or reduce the
> > heritable differences which selection could act to select between.
> 
> In all forms of group selection, intra-group selection against altruism
> is effective (by definition of altruism).  Hence, altruistic groups
> decrease in altruism, while mostly selfish groups decrease in altruism
> to a lesser extent.  Hence intergroup variation tends to decrease.  And
> hence selection between groups has less raw material to work with.  We
> need a mechanism to restore variation between groups.  Without such a
> mechanism, group selection runs out of gas.  That is the heart of the
> classical (1960s) argument against group selection.  (And it is my
> understanding of the thrust of those three references that we can't read,
> is that they close the door to the possibility that kin selection without
> kin recognition might provide an exception to this classical argument if
> we just tune the viscosities right.)
> 
> Outbreeding as such, doesn't necessarily help restore intergroup variation.
> But the periodic dissolving of groups into the general population and the
> creation of new groups from the common pot MIGHT help.  It could do so if
> there is assortive group formation (but now we need an explanation for THAT!).
> Or, it could do so if the newly formed groups are small enough that we get
> the needed variation between groups from simple sampling error.  The Perrin
> quote and the Sterelny example discussed elsewhere seem to make use of
> assortive group formation.  The example described in "Unto
Others" makes
> use of sampling errors.
> 
> I hope that explains it.

I can see how assortive group formation might generate variation between 
groups - e.g. if all the green skinned folks seek each other out as 
bedfellows - and all the blue-skinned folks do the same.

I'm not sure "outbreeding" is a good name for that, though - you soon get 
groups consisting primarily of each type - and then "outbreeding" rapidly
becomes a very misleading term for what's going on.

Genetic drift is bound to produce some between-group variation.

Regularly ripping groups up and reassembling them at randomly, seems
likely to generate more variation.  Unfortunately, while the number of 
groups selection looks at goes up - the time selection has to 
evaluate each one goes down.
-- 
__________
 |im |yler  http://timtyler.org/  tim{at}tt1lock.org  Remove lock to reply.
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