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

I have snipped most of this post because TT and I have both expressed our
views effectively and our differences have been made clear.  It seems we are
at an impasse on several points, and we can leave it at that.

in article [EMAIL PROTECTED], Tim Tyler at [EMAIL PROTECTED]
wrote on 11/11/03 9:06 AM:

>> To add a nod to the kind of work I am currently engaged in, it is easy to
>> show with computational models that gene flow is necessary for the emergence
>> of genetic divergence between subpopulations [...]
> 
> ? They cannot diverge genetically if they are completely isolated from
> one another...?

The system cannot self-organize if there is no communication among the
components (subpopulations in this case).  If you explore a computational
model of evolution in a spatially explicit context, you can ASSUME lack of
communication between subpopulations and divergence happens.  Of course you
have only learned what you assumed in that case.  If you allow for limited
gene flow among subpopulations in a stepping-stone model, or among locations
in a more general model of isolation by distance, then you can observe
emergence of spatial boundaries between gene pools that you did not assume.
This way you can learn about how such local subpopulations can evolve
without just a circular confirmation of an assumption.  Divergence among
subpopulations in this way requires gene flow.

>>> 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.''
>> 
>> This is ONLY the case if you limit your definition of what constitutes group
>> boundaries to patterns of genetic distinctiveness, and the mode of
>> inheritance (at the group level in the current context) to genetics.
> 
> When discussing group selection, we are usually talking about "biological"
> groups - as characterised by their gene pools.

I don't know who "we" is meant to include, but it does not include me or
many others I know in the field.  We (I don't think I am excluding anyone
here) have a long and strong tradition of population genetic modeling that
has naturally been used as a framework for modeling group selection by some.
I don't think I ever read a claim in such papers that this was meant to
preclude other ways of characterizing biological groups.

> If you want to broaden things to discuss the evolution of (e.g. political
> parties), then I'll be happy to admit that those may evolve via all
> sorts of forces - possibly including "group" selection (selection
> between the parties).
> 
> However the link back to the sort of evolution as described by
> changes in allele frequencies is a tenuous one.

It may be.  I never claimed that group selection has, for example, a
stronger or even equivalent influence on the evolution of allele frequencies
compared with selection at the individual level.  I am arguing that genetics
is only one mode of inheritance among many, and it is a particularly
important mode at the individual level.  In the big picture of multilevel
selection, different modes of inheritance can be more or less important at
different levels of biological organization and these modes are merely
constraining mechanisms encountered by natural selection.  Darwin and
Wallace, for example, did not know about genetics and their notions of
heritability mechanisms at the individual level were somewhat inconsistent
with the genetic mode.  This, however, did not get in their way of
developing an excellent understanding of how selection works, without
relying on any particular mode of inheritance.  I think they were right in
assuming that natural selection is a process that depends upon heritability,
but not having any particular mode of inheritance.

[snip]

>>> 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.
>> 
>> Interesting idea.  Do you know if this (there must be limited gene flow
>> between individuals to permit selection at the individual level) appears in
>> publication anywhere?
> 
> My comments above are - I believe - paraphrasing some of Dawkins
> explanations of why the individual level is worthless.
> He refers to it as the "internal fragmentation destroys copying
> fidelity" issue [TEP, p.99] - and writes:``It is therefore better not to
> speak of adaptations as being for the good of the organism'' [same].

Ah yes - now I recognize the idea.  As usual, I find the core of the idea
intriguing, but Dawkins' interpretation wanting.

>>> 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.
>> 
>> I see a few points here to take issue with.  First, I don't see how undoing
>> the effects of group selection would necessarily reduce the heritability of
>> group level traits. [...]
> 
> It removes group differences - with the result that group selection
> has no variation to work on.

This would depend on the relative frequencies of stabilizing vs.
diversifying group selection, which I don't think we understand at this
point.

>> Second, just because individual selection can interfere with group
>> selection does not mean that it usually does, nor that it would be
>> an important factor. [...]
> 
> Nontheless, individual selection is likely to care passionately about
> most aspects of most organisms; there is little that is irrelevant to it.
> 
> Group selection will have the best chance when affecting traits that
> individual selection acts weakly on - but I suspect this category
> consists of lean pickings.

I agree with the essence of your point, without sharing your view that
selection at the individual level has a big advantage in control over
evolution to overcome.  In the big picture of evolutionary time, I agree
with those who argue that the primary level at which selection occurs is
marching its way up the levels of biological organization.  In the beginning
it was the gene, then the gene network, then the cell, then the
multicellular organism, then groups of multicellular organisms, ...

This view contrasts with the Dawkins view that selection has stayed mainly
at the level of the gene, and the rest represents macroscopic constructions
of genes that do not take over as levels of selection.  IMHO, the structures
of meiosis and mitosis as genomic processes alone provides overwhelming
evidence against the Dawkins view, because they generally remove fitness
differences among genes at the stage of gene reproduction.

Cheers,

Guy