Re: Levels of selection (Was: Can cognition override natural

Guy Hoelzer <[EMAIL PROTECTED]> wrote or quoted:
> [EMAIL PROTECTED] wrote:

>> With the corporation example, that might translate into the corporation
>> going bust *because* of deficiencies of its workers.  If so, then
>> we are still seeing effects due to some individuals working better
>> than others - and we *are* seeing differential individual-level success.
> 
> As your view is becoming clear, this is a consistent response on your part.
> I will use this analogy to further explain my perspective.  Even if the poor
> performance of the corporation was due in part to the poor performance of
> some of the employees, the death of the corporation probably takes down many
> good performing employees, as well.  In fact, all of the employees suffer
> independent of their quality.  The same is true of the death of an
> individual organism.  It takes out the good performing genes along
> with the poison gene.  The process did not selectively distinguish
> among genes in the genome.

Yes.  However the extinction of the good genes is likely to be largely
at random.

The good genes have little control over whether they are in a body
with bad genes.  A sexual population, and independent assortment
see to that.

There may be some non-random effects due to linkage with the
bad genes - but basically selection acts on the good genes at
random - and so has no sytematic effect on their frequencies.

>> With this sort of perspective, genes and species make sense as
>> units which can be selected - whereas individuals and groups do
>> not - they usually mix themselves together too much in each
>> generation.
>> 
>> It is well established that group selection can only arise if
>> there are barriers to gene flow in the population - and that
>> those barriers neet to restrict gene flow a lot if there are
>> to be adaptations that can be said to be for the benefit of
>> groups.
> 
> I think this is an outrageous claim.  The only folks who think that any such
> thing is "well established" are the gene-selection advocates.  There is
> absolutely no way in which the process of group selection is dependent on
> genes or gene flow.

I don't think I was trying to say anything contraversial here.

For group selection you need heritable variation among the groups.

If groups share genes then that will tend to reduce variation
between the groups.  If they do it too much then it is going
to become hard to find heritable differences between the groups.

The critical threshold is somewhere around one individual per
generation.  I would describe that figure as a low one.

``If fewer than one individual per generation moves from population to
  population, so that the amount of gene flow is very low, then
  populations will develop fixed differences through natural
  selection. Fixed differences are what they sound like -- differences in
  which alleles are fixed in different populations. That is, for a gene
  with two alleles (say D and d) allele D could be fixed (the only allele
  present) in one population and allele d could be fixed in the other
  population, and this low level of gene flow would not be enough to
  change that. 

  In contrast, if large numbers of individuals move from population to
  population , so that the amount of gene flow is very high, the
  populations will essentially be like one single population and will
  have the same alleles, in the same frequencies, even if they occur in
  somewhat different environments so that differences might otherwise
  tend to evolve through natural selection. Large amounts of gene flow
  will thus mask the effects of other forms of evolutions and make
  populations similar.''

 - http://www.utm.edu/~rirwin/391DriftFlow.htm

We've discussed this point before - several times - e.g.:

``:> : Does your question imply that you think group selection can only
  :> : occur through the differential survival and reproduction of groups
  :> : with relatively non-leaky boundaries?
  :> 
  :> We discussed this before.  You need groups, with distinctive traits,
  :> for group selection.
  :> 
  :> Too many leaks and you wind up with one big homogenous
  :> group.  Population genetic folk wisdom puts the acceptable leak
  :> rate at about one individual per generation.  The figure is
  :> independent of the size of each group.
  :> Though in practice this figure seems to be a bit too small. 
  :
  : This figure is derived from the Island model of migration, 
  : so it depends on equality of group sizes, the absence of spatial
  : constraints to movement, and so on.  In practice, this figure can be
  : way off.  But I digress.
  
  ;-)
  
  The model does indeed have some questionable assumptions - and
  experimental tests in ecological situations have found it to be too
  low.
  
  However the basic idea still seems sound - migration easily destroys
  the identity of groups, very low levels of migration are all that
  is needed, and these low levels of migration are not very common in
  nature.''

>> It's the same with individual selection.  For there to be
>> adaptations that favoured individuals, you would need there
>> to be restricted gene flow between individuals - and the
>> restriction would have to be pretty severe.
> 
> I would say that there is very rarely gene flow between individuals.  An
> exception would be tissue transplants.

I meant across generations.

In an asexual population there is no gene flow between individuals
across generations - no mixing - but in sexual populations genes are
thoroughly mixed between two individuals in each generation - resulting
in substantial gene flow.

>>>> He considers species to be selectable (e.g. see p.106-107 of TEP) -
>>>> but thinks that gene-level selection is faster and more important.
>>> 
>>> I would certainly agree that species selection would happen much more
>>> slowly, but slower surely does not mean less important.
>> 
>> In the case of species selection it quite likely does - since slower
>> equates to a weaker pressure generating adaptations.
> 
> To understand multilevel selection theory I think it is essential that you
> try to step out of your perspective of the world as an individual, a
> particular level at which selection can operate.  I agree with Darwin's main
> point that natural selection can cause adaptive evolution.  He only explored
> (through deep thinking) selection and adaptation at the individual level.
> The link between the level of selection and adaptation is maintained under
> multilevel selection theory.  Therefore, adaptations and the rate of
> adaptive evolution at the individual level are not relevant to the
> importance of selection and adaptation at the level of the group
> (including species).

I don't see how that can be true.  If individual selection can undo
the effects of group selection in the time that groups take to
reproduce, then it will destroy any heritable variation between the
groups in the process - with the result that selection between the
groups will have nothing to work on.

There really is a race on between selection on the different levels.

The generation time for group selection is slower.  It *does* get to
kill a lot of individuals at once when it happens - but (probably)
not in numbers comparable to selection between individuals in the
interim.
-- 
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 |im |yler  http://timtyler.org/  [EMAIL PROTECTED]  Remove lock to reply.