Tim Tyler  wrote:

> Jim McGinn  wrote or quoted:
> > Tim Tyler wrote:
> 
> > > This is all after distinguishing "species
selection" from "species
> > > sorting" - and *only* considering the former.
> > 
> > There is absolutely no difference between sorting and
> > selecting.  So this is a distinction without a difference.
> 
> This distinction is one made by Gould, Eldridge and Vrba.
> 
> Since they are major proponents of these ideas, it is worth
> looking at what they are saying.
> 
> According to their classification scheme, "selection" processes are
> a subset of "sorting" processes.
> 
> An explanation of the distinction they make may lie beyond my
> scope here - and I may have to refer readers to "Ever Since Darwin" -
> and other such works by these authors.
> 
> However - briefly - they categorise effects such as extinctions
> of large organisms during asteroid impacts as species sorting -
> and *not* as species selection.
> 
> They argue that the survival criterion which is being "examined" by 
> selection (namely body size) in such cases is better regarded as a 
> property of individuals than it is a property of the species.
> 
> During such impacts, species go extinct primarily as a result of the 
> deaths of the individuals in question, due to individual-level
> selective factors.
> 
> An individual-based model would explain the results perfectly well,
> if periodic mass extinctions were modelled.
> 
> This would be a case where a species-level explanation would provide
> no additional insight - since it would make all the same predictions.
> 
> They reserve the term "species selection" for cases where selection
> "examines" "properties of the species".  These are
necessarily emergent
> properties - not simply aggregates of the properties of the individuals
> that make up the species.  Species reproduction rate would be an example
> of a species-level trait - a trait of the species not easily predictable
> from examination of the individuals of the species, or in any way a sum
> of individual reproduction rates.
> 
> There's even a case for describing the studies of group selection on 
> Tribolium - e.g. where factors such as infertility and high mortality
> were group-selected for - in studies like:
> 
> ``Group selections among laboratory populations of Tribolium.''
> 
>  - http://calorierestriction.org/pmid/?n=1070012
> 
> ...as "merely" sorting.  Although here whole groups were being 
> extinguished, the properies of individuals were what was being
> "examined" by the selective agent.  Selection never even
> looked at the properties of the groups - let alone selected
> between them.
> 
> John Wilkins has a pithy summary of the whole idea:
> 
> ``Recent work by Gould, Eldredge and Vrba [refs in Sterelny 
>   1995] amends this from species selection to species sorting, 
>   what Vrba calls the 'effect hypothesis'. This is a view that 
>   now has wide acceptance amongst biologists, including 
>   Williams [1992]. Groups are thought to survive extinction 
>   events differentially, based on adaptations of their 
>   component organisms, so the organisms are adapted, not the 
>   groups.''
> 
>  - http://www.biologie.uni-hamburg.de/b-online/e36_talk/reduction.html
> 
> However, having looked at the distinction being made - ISTM that there
> is a good case to be made that they are splitting hairs; that properties
> of individuals are *fundamentally* properties of the species they compose -
> and that the simplest thing to do would be to describe the whole
> kit-and-kaboodle as "species selection" - as I believe you (i.e. Jim)
> would probably argue.

Actually, there is a basic problem of logic here. This is the fallacy of
composition, nicely illustrated by Williams in his 1966 book about the
(non-hair-splitting) distinction between a herd of fleet deer and a
fleet herd of deer. The properties of a whole are not those of the
parts, nor vice versa.

Sorting can occur on aggregates as much as on particles. Selection can
only occur on reproducing particles, and so if species are subjected to
selection, they must behave as particles in that process. It is my
opinion species do not ever behave as particles in a process unless the
species is co-extensive with a single localised population.

Gould has returned to species selection in his Brick; I don't know why.
I think it is a largely semantic move on his part, but Larry will soon
correct me on that.
> 
> Adopting this position would confound the theories of "species
selection"
> and "individual selection" - so that they would sometimes be the same
> theory and would make all the same predictions - but that would 
> probably not be *too* unacceptable.
> 
> Whatever terminology and classification is ultimately adopted, it's 
> currently important to bear this terminology in mind in these discussions.
> 
> If the term "species selection" crops up, one of the first
things I want
> to know is whether this is referring to differential success of species -
> or to Vrba, Gould and Eldridge's refinement of this idea to exclude the
> cases explained by individual-level selection.
> 
> The distinction is likely to make a substantial difference to the 
> answers to questions such as whether species selection is common or 
> important.


-- 
John Wilkins
john_SPAM{at}wilkins.id.au   http://www.wilkins.id.au
"Men mark it when they hit, but do not mark it when they miss" 
                                               - Francis Bacon
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