From: colby@bu-bio.bu.edu (Chris Colby)
Newsgroups: talk.origins
Subject: Re: Chris Colby's Evolution FAQ: What is hierarchy?
Date: 12 Oct 92 22:38:09 GMT
Organization: animal -- coelomate -- deuterostome


"... the nested structure of the biotic realm emerges as the simplest,
and strongest, prediction of what biologists _must_ observe if the 
general notion of evolution is true." -- Niles Eldredge, 1989

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". In this posting I will attempt
>to demonstrate that current classification schemes are hierarchical in 
>the same sense that military ranks are hierarchical but that this is very
>different from claims that "evolution is a hierarchical process" or that
>"patterns of diversity are hierarchical".

I state explicitly in my FAQ that evolution is not progress, and I don't
think that a hierarchy of traits implies progress. I will argue that
biological traits are distributed in a hierarchical fashion across taxa,
but I won't argue that evolution is a hierarchical process. [In the FAQ 
I don't claim that evolution is a hierarchical process (although I would
if a discussion of gene family evolution were included).]

>First of all, let's be clear about the definition of the word "hierarchy".
>If you look in your favorite dictionary

Ah, dictionary wars... USENET at its finest 8-) I accept this definition
of hierarchy (because, you know, it _is_ the definition of hierarchy).

>It is quite correct and
>proper to state that biological classification schemes are hierarchical
>in organization.
 
Agreed.

>Now, let's see what Chris Colby says in his FAQ.

>   "Further strong evidence for macroevolution comes from the fact 
>    that suites of traits in biological entities fall into a
          ^^^^^^^^^^^^^^^^
>hierarchical pattern

>     Capital letters designate traits --
                                ^^^^^^
>    these are shown both where they arise and how they are distributed
>    in species.                                   ^^^^ (i.e. traits)

I've underlined a few key words because I'd like to make it clear
that I am talking about traits (not organisms or species) being
arranged in a hierarchy. All species would be at the same level so
it is improper to speak of "higher" or "lower" species (although
this terminology crops up all time in the literature.)

>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.

Actually, I agree with Andy (from a separate post) that "nesting" may
be a more appropriate term. To me, a hierarchy implies nesting because
each lower level contains more entities than higher levels. But, I can
see this is not explicitly included in the definition. "Nesting" (IMHO)
seems to bring the point across much better than "branching" (or, I must
admit, "hierarchy"). If a hierarchical distribution and a nested
distribution are not synonomous then I have indeed misused the term.
I've always thought they were the same thing.

>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.

No, species would be at the lowest level and the process of evolution
results in biological traits being distributed amongst taxa in a
hierarchical (nested) manner. For example, the trait "hair" would
be at the highest level within a mammalian hierarchy, at the next
lower level, the traits defining "monotreme" and "traits shared
by marsupials and placentals" would reside. Shared marsupial traits
and shared placental traits would be on the next lower level within 
the marsupial/placental lineage and so on. 

I don't see how anyone can
confuse this with progress unless more derived traits are seen as
progress. (In the literature, traits are often refered to as "primitive"
or "advanced" when (IMHO) "ancestral" or "derived" would be a better
choice of words. The idea of progress in evolution seems to die hard
in evolution, but I can't see how the word "hierarchy" in any way
implies progress.) Even if derived traits were seen as progress,
then progress would be being made in every lineage -- the usual
misconception is that evolution is linear progress leading from
bacteria to man. (Also, if derived traits indicated progress, the
arrow of progress would be down the hierarchy, not up it.) 

>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. 

I don't see how that follows.

>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?

Species selection has been posited by paleontologists to be a
mechanism working at a level above the species level in evolution.
(See Eldredge, 1989, Macroevolutionary Dynamics, McGraw-Hill, New York
for a discussion of this.) Species selection was coined by Stanley in 
1975 -- according to him _species_ had differential reproductive success
and declared "Macroevolution is decoupled from microevolution". Gould
and Eldredge, in thier 1977 punk eek paper claimed "anagenesis is only
accumulated cladogenesis filtered through the directing force of species
selection." (Both these quotes reappear in Futuyma on page 402, BTW).

Eldredge, in his 1989 book, appears to back off that claim and claims
that "species sorting" (the observation that species have differential
repro success) could be due to either "species selection" or the "effect
hypothesis" (Vrba, 1980)-- the sorting of species arises from processes 
resulting at a lower level. Eldredge then goes on to claim that species
selection is analogous to sexual selection (which he contrasts with
natural selection). Personally, I think species selection is bullshit
and that evolution does not have a(n upper) hierarchical component.
Or at the very least, it has not been a significant factor in macro-
evolution.

>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.

I hope the above clears that up. See chapter 5 in the Eldredee book
for a more complete summary (or go to Stanley's original paper).

>Laurence A. Moran (Larry)

Gould and Eldredge, 1977, Punctuated equilibria: the tempo and
mode of evolution reconsidered, Paleobiology 3: 115-151

Stanley, 1975, A theory of evolution above the species level,
PNAS 72: 646-650

Vrba, 1980, Evolution, species and fossils: How does life evolve?,
S. Afr. J. Sci., 76:61-84

(I have not read the last two papers and am only providing their
references in case anyone is interested. I'm relying on Eldredge's
book to be accurate in the description of their work. Since Eldredge
has published papers with both Stanley and Vrba, I'll assume he is
characterizing their arguments fairly.)

Chris Colby 	---	 email: colby@bu-bio.bu.edu	---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
 	--Kurt Vonnegut from "Galapagos"

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