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FW: Re: FW: Help with Cladistics



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---------------Original Message---------------
I need some answers to a few question regarding cladistics.

The first question is with regards the the book "Darwin on Trail" by
Phillip E. Johnson. On p134 he talks about the controversy over the use of
cladistics in a British Museum of Natural History. He states the "What was
wrong with all these exhibits, according to Halstead, is that they employed
a system of classification known as cladism, which assumes that no species
can be indentified as the ancestor of any other species." In a note on the
same page he states "...cladograms show relationships among living and
fossil species, but never ancestoral relationships."

Johnson through out the book launches a savage but heavily flawed (IMHO) on
Evolution. I feel that he uses these definitions of cladistics to bolster
his opinion that the fossil record shows no transitional species. Can
someone give me an answer regarding cladistics and ancestoral species?

The next request is one regarding Archaeopteryx. Using cladistics is
Archaeopteryx regareded as a bird?


This concern I believe was previously answered by a geologist at UT Austin
whose name I have since forgotten.  

His contribution was on the mark, but I wish to emphasize a few points that
may further shed light on "cladistics".

As for the attacks of Johnson, this is typical of creationists.  Michael
Benton's "Evolution: A Theory in Crisis" is another example of misunderstood
claims.  

Donn Rosen and Colin Patterson (Patterson is at the British Museum), two of 
the
early proponents of cladistics, together,in a series of papers on
the treatment of fossils in phylogeny reconstruction (Rosen and Patterson,
1977; Patterson, 1980; Rosen et al. (1981) argued (and has been subsequently
accepted today) that ancestors can not be discovered.  It is here where 
Johnson makes his illogical extrapolation.  

What Rosen and Patteron were addressing was the traditional manner by which
paleontologists reconstructed phylogeny (phylogenetic trees were around long
before cladistics).  This research program centered around the search for
ancestors that could CONCEIVABLY have given rise to the organisms under 
consideration.  Herein lies the problem.  How does one determine objectively
what the ancestor of say, four-legged vertebrates looked like?  There are
a number of good choices of lobe finned fishes to choose from:lungfishes,
coelacanths, fossil fishes belonging to the Order Osteolepiformes, Porolepi-
formes, the family Panderichthyidae, and so on.  I limit the choices to these
because all paleontologists agree that the lobe-finned fishes, those fishes
with bony fin elements, not the ray-finned fishes (= most other fishes)
are closer in propinquity to four-legged vertebrates.  The point is, there
IS no way to tell.  Paleontologists relied on ad hoc scenarios associated
with their choice of ancestor based on a structure they deemed most important
in leading to the four-legged vertebrates.  These scenarios were completely
subjective, and varied from worker to worker.  Science deals more with facts,
and less with opinion.

In this sense, Rosen and Patterson suggested that the focus of the research
program shift from the search for ancestors, to the search for *sister taxa*.
This is where cladistics comes in to play.  We cannot know the processes
of how evolution happened, but we can look for clues as to the pattern by
which it proceeded.  This is what cladists do.  The clues are locked inside
the organisms as the attributes they share.  

"Transtional forms", such as Archaeopteryx, ARE transitional, in that they
have certain features in common with all dinosaurs (e.g., a hole in the hip
socket) and features of modern birds (e.g., feathers).  The reason 
Archaeopteryx is CLASSIFIED as a bird, and this is where cladism stands
alone amongst evolutionary disciplines, because it shares *unique*
characteristics only found with modern birds, and it is those and only those
characters that indicate geneological relationship.  A cladistic 
classification only classifies organisms on the basis of shared derived 
characters.

The only thing "knowable" are the taxa and the characters they possess.
Characters among recent organisms serve in many respects, the same function
as fossils.  Characters can remain unchanged for millions of years due
to selection pressures and so on.  We use such data to hypothesize 
relationships
among known taxa (fossil or extant).

So the Creationists need to do more background reading on the subject of 
evolution, particularly cladistics.  But if that were to happen, there
would be no need for expositions such as these.


Kevin R. Toal
Department of Biological Sciences                                            
 
Southeastern Louisiana University
ktoal@selu.edu

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