"Guy Hoelzer"  wrote in message
news:c7hmdp$i5v$1{at}darwin.ediacara.org...
> in article c7eik8$2iac$1{at}darwin.ediacara.org, Perplexed in Peoria at
> jimmenegay{at}sbcglobal.net wrote on 5/6/04 4:44 PM:
> > I think that it is important to distinguish two different kinds of
> > "top down effects".   The fact of frequency dependence
at the individual
> > level means that the structure of polymorphism is potentially an
emergent
> > (my static sense) trait at the species level.  However,
> > this doesn't necessarily mean that it is a stable or heritable
species-level
> > trait, nor that this trait is subject to and/or maintained by
species-level
> > selection.
>
> I agree with your last point on two grounds.  [snip]
> However, I don't see in your paragraph a description of "two different
kinds
> of 'top down effects'."  Can you please describe these categories?

Sorry, I was probably misinterpreting what you meant by a top-down
effect.  The distinction I wanted to make was between top-down control
and top-down selection.  An example of top-down control would be a
polymorphism stabilized by frequency dependent selection at the lower
level, because that particular frequency pattern is an ESS at the higher
level.  An example of top-down selection would be the unlucky fate of
a selfish individual (or type) who does well within the group, but suffers
from extinction of the group in competition with a more cooperative
group.  Only the second kind of "top down effect" is a hallmark of
species-level selection.

> > Let me ask about two other examples of polymorphism. [snip response]

Thanks. I am happy to see that you are not a "pan-species-selectionist".
Some polymorphisms result from species selection, others do not, you say.
Interrogation completed.  I am willing to join you in your "heresy".  But
I probably would chose different examples of polymorphisms which I
would suspect of being maintained by species-level selection.

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.
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