From: adpeters@sunflower.bio.indiana.edu (Andy Peters)
Subject: Re: Chris Colby's Evolution FAQ: What is hierarchy?
Organization: Program in Evolution, Ecology, and Behavior, Indiana University
Date: Mon, 12 Oct 1992 04:44:43 GMT

In article <BvznKo.B0z@gpu.utcs.utoronto.ca> lamoran@gpu.utcs.utoronto.ca (L.A. Moran) writes:
>
>I believe that Chris is misusing the word "hierarchy" in his FAQ and that
>he is conveying a false notion of "progress".

"Hierarchy" does not connote "progress" to me.  Therefore, upon my first
reading of this post, I was prepared to jump to Chris's defense for his
use of the word.

Thinking about it further, however, I realized that the word might have
the connotations for me that it does precisely because I have always 
thought of the evolutionary relationships of organisms as being hierarchical.
Since I do not see evolution as progressive, my notion of evolution could 
have shaped my notion of the word "hierarchical" rather than the other way 
around.

My dictionary defines "hierarchy" much the same way as Larry's does.  It
definitely associates the word with the application of rank to some
levels over others.  Therefore, unless there are lots of other people
for whom "hierarchy" does not connote "progress," I will agree with
Larry that Chris's use of the word is not appropriate.

[much deleted]

>There is no "hierarchical pattern" in evolution. The fact that humans choose
>to create a hierarchical classification system does not mean that one can
>describe evolution as hierarchical. The classification scheme refers mostly 
>to living species - it is independent of the mechanism that gave rise to the
>species that we see today. I think that Chris should be using "branching" to 
>describe the pattern of dendrograms. It is much clearer to say that the 
>"branching" pattern is what one expects to see in evolution since living
>species have evolved from common ancestors.

This is where I disagree with Larry.  I don't think "branching" is
a descriptive enough word in this case.  While a branching pattern
is expected if evolution has occurred, the most striking feature 
expected is that of *nesting*; more recently-split groups nest 
perfectly within groups formed by more ancient splits, and
those groups nest perfectly within groups formed by yet-more-ancient
splits, etc.  While this is a logical result of branching, I think it
is explicitly nesting, and not branching, which is observed, and
cited as evidence for evolution

>I also believe that Chris has his hierarchies reversed. He seems to be 
>claiming that the species is the highest rank and that the process of
>evolution produces a hierarchy over time. When he says that microevolution
>leads to a hierarchical pattern of genetic diversity he is making a statement
>that sounds very much like claiming "progress" in evolution. He also implies
>that there are some scientists who believe in hierarchical processes in 
>evolution; Chris, what are these hierarchical processes that you are referring
>to?
>      [quoting Chris Colby:]
>      Some PE proponents envision the theory as a hierarchical theory
>      of evolution because they see speciation as analogous to mutation  
>      and the replacement of one species by another (which they call
>      species selection) as analogous to natural selection. Speciation
>      adds new species to the species pool just as mutation adds new 
>      alleles to the gene pool. Likewise, they argue that species
>      selection favors one species over another just as natural selection
>      can favor one allele over another. This is the most controversial
>      part of the theory. Many biologists agree with the pattern of
>      macroevolution these paleontologists posit, but many disagree with
>      the mechanism -- species selection. Critics would argue that species
>      selection is not analogous to natural selection and therefore
>      evolution is not hierarchical."
>
>I don't understand this description of the ideas of some "PE proponents"
>and I don't understand what Chris means by a "hierarchical theory of
>evolution". I hope that he will try to explain more claerly.

What I think Chris is saying is that "some PE proponents" suggest that
different mechanisms of evolution work at different levels of nesting/
branching - work at different levels in the hierarchy.  Since different
processes work at different levels in the hierarchy (given that one
accepts the use of the word "hierarchy" in the first place), the processes 
themselves can be seen to be hierarchical.  In other words these "PE
proponents" are proposing that species-level processes and individual-
level processes are two different things.

I think that it is undoubtedly true that there are some things that 
happen at the species level that do not happen at the individual 
level - emergent properties of the species, if you will (to 
use yet another buzzphrase).  To take an example from my own 
field:  it has been postulated that sexual lineages, because 
of the variation generated by sex, tend to speciate at a more 
rapid rate than asexual lineages; therefore there are more
sexual species than asexual species.  This is undoubtedly true (given
the right definition of species); what is more, it is a species-level
phenomenon that explains an observed "pattern of diversity."

The question which I think arises is:  are such "species-level"
processes generally important?  I think the sex example I gave above
is true, but almost trivial:  sex still has to be maintained at an
individual level to make the species-level processes possible at
all, right?  Such species-level explanations can't function unless
there's an individual-level explanation to make them possible; in
such a case, is the use of the term "hierarchical" acceptable?

>Laurence A. Moran (Larry)

-- 
* Andy Peters                     * "Slugs are small and portable    *From
* Program in Evolution,           * Just stuff 'em up your nose      *"Slugs,"
*      Ecology, and Behavior      * They'll fit beneath your armpits *by David
* Indiana University, Bloomington * Or right between your toes"      *Greenberg
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