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

Guy Hoelzer <[EMAIL PROTECTED]> wrote or quoted:
> in article [EMAIL PROTECTED], Tim Tyler at [EMAIL PROTECTED]
>> Guy Hoelzer <[EMAIL PROTECTED]> wrote or quoted:

>>> More importantly in the context selection at the level of the gene, it
>>> does not include any aspect of fitness.  The nearly universal mechanism
>>> of mitosis, and meiosis in diploid (and higher ploidy level) sexual
>>> species, eliminate fitness differences among genes at the gene
>>> level.  The norm is for every gene copy to be copied exactly once, or
>>> have equal chances at being represented in gametes.  This means that
>>> there is virtually no heritability of fitness at the level of the gene.
>> 
>> What?
>> 
>> Say the gene codes for a fatal poison.
>> 
>> Isn't that highly likely to result in it being selected against?
> 
> It is indeed highly likely that individuals carrying this mutation would be
> selected against at the individual selection level, and that a consequence
> of individual selection in this case would be extirpation of the allele from
> the gene pool.  If this was a dominant lethal mutation, I think the level at
> which selection acted becomes somewhat ambiguous.  Indeed, if the mutation
> did not get passed through even a singular cellular reproduction, then the
> distinction between gene, cell, and organism levels would be moot.  Why do
> you think that this would be an example of selection at the level of the
> gene?

I doubt I would say such a thing.  Selective events can't necessarily be
pinned down to a particular level - they can affect multiple levels
simultaneously.

Here the selection is affecting the frequencies of the genes in question;
that's enough for me to say there's an element of selection between genes
going on.  The genes are showing up in the phenotype to a sufficiently
great extent for them to show differential reproductive success.

If you only allow S.D. events to count as selection between genes,
then gene-level selection is obviously not very important.

However, you should be aware that you are then on a different planet -
and are using a different vocabulary - from most other players - and
from all of those who advocate gene-level selection.

>> Selection on genes happens when the organisms that carry them die -
>> or fail to reproduce.  That process kills genes *just* as much as it
>> kills organisms.
> 
> Yes, but it is not selection at the level of the genes.  This is an example
> of effect cascades emanating from one scale of existence to another.
> Corporate competition can cause a business to go under and the loss of jobs
> for its employees.  I would argue that the relevant process happened at the
> scale of the corporations, not at the level of individual employees, which
> had to suffer the cascade of effects across levels.

If the gene frequency was unchanged, I would not describe it as
involving gene level selection.  Or if I could be convinced that
the genes were not responsible for the selection - e.g. it was
due to chance - then that wouldn't be selection acting on genes
either.

However in my example, the "fatal poison" caused - or contributed to -
the mortality of its bearers.

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.

>> Meiotic drive is *not* the only way genes can be selected.
>> They get selected against every time the bodies they are in die.
>> Individual death causes gene selection - not just individual selection.
> 
> The fact that fitness differences at the individual level affects changes in
> allele frequencies does not imply that the process of natural selection
> actually manifested at the gene level, IMHO.

For me, alleles are still getting selected.  Even if more than one
is picked at once.

>> Dawkins doesn't regard the individual as a selectable unit -
>> basically saying that sex scrambles it up too much from
>> generation to generation for any individual to be said to
>> have a frequency in the population that can increase or
>> decrease.
> 
> Does he say why this should matter at all?  It seems to me that this
> argument follows from the assumptions of the way we model selection in
> population genetics, rather than from the theory of natural selection.

With genes you can at least measure success - by counting copies.
However, with sexual individuals you can't do anything equivalent.
Each one is unique.  They (almost) all have a frequency of one.

The nearest thing you can do is count descendants.  However that
doesn't work very well.  In short order either the entire population
is a descendant of yours - or your line goes extinct.  Even if
everyone is descended from you, that doesn't mean any of your genes
survived - even if everyone in the population is your descendant,
all the genetic information you carried may have been wiped out.

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.

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 don't think that's what we see - instead there is practically
unrestricted mixing.  The typical rate of gene flow between individuals is
not down a the level of a gene per generation (where selection might
stand a chance of countering it) - it's half their genome per generation.

In most groups - and nearly all sexual individuals - there is too much
genetic mixing for adaptations at that level to arise.

>> 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.

I'm not sure what the best analogy might be.

Perhaps imagine a tank with a sail on top.

The location of the tank is its phenotype, the tracks of the tank
symbolise gene-level selection and the sail on top of it represents
species selection.

The sail on top might well make a difference to the eventual
location of the tank - if the wind consistently blew in the
same direction for a long time - and if the operators of the
tank's tracks had no care about where they wanted to go.

However, most of the time, the tank's owners would have an agenda
of their own.  The existence of the sail on top of the tank would
not wind up making much difference to its eventual location.

One of the best examples of species selection I can think of is
the pressure in animals towards small size - caused by repeated
asteroid impacts systematically eliminating large animals.

Despite the species-level selection for small size, the largest animal
that has ever lived is one that is with us today.
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