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Re: cladobabble.../Some clarification... (long)



Some very useful comments have been made about this issue.

Chuck Prime wrote (11/17/97; 8:51p):

>Of what use would this forum be if pursuit of proper understandings
>were forbidden on it?

Our host has suggested not taking much time to discuss cladistics here, 
unless it has direct bearing on dinosaurs.  (Or have I misinterpreted his 
words?)  My comments will eventually get back to dinosaurs.

>Your paraphrase lumps together "metaphysics" (the study of the nature
>of reality) with "epistemology" (the study of the nature and acquisition
>of knowledge).

Yes, I see where that happened.  Good point.

Chuck's second rephrasing is what I meant:

>. . . "The clade Maniraptora [is a classification which I or others 
>will continue using], no matter what [animals it might refer to]."

>About the only thing I know about cladistics is that it is an 
>intellectual method of classifying (certain?) animals. As such, the 
>CLADE is an epistemological tool which does not exist in material 
>form--even though papers outlining it do, the fossils referred to by 
>it do, the animals who were fossilized did...

I agree that clades do not exist in material form.  Previously some 
discussants claimed that they are the REAL objects out there, but I 
disagreed, saying animals themselves and fossils are the only real 
objects.  I can hit you over the head with a fossil, but not with a 
clade; clades are mental constructs (hope I used that term correctly).

Tom Holtz said (11/18/97; 8:35a):

>Actually, a clade (from Greek clados, branch) is any monophyletic group:
>an ancestor and all its descendants.  Accepting, based on other data, 
the
>existence of evolution as modification with descent, there exist real 
>clades in nature external to human reality.  

Now maybe I am being overly reductionist, but as mental constructs, 
clades
would not exist in nature external to human reality.  So, they are either 
not what I say they are, or not what Tom says they are.

>We can propose names for real clades based on the relationship of any
>two taxa (or one character, but (as discussed earlier) there is a chance
>of homoplasy spoiling such definitions). 

So, the definition of a clade depends on an earlier determination, which 
may not be true.  It seems that we define clades in general, then try to 
see what the specific ones are.  Specific clades aren't really 
defined--they're identified.  Right?

Then Tom said:

>One goal of systematics, then, is to determine (based on a particular
>data set) what are the characters which diagnose these clades and what 
>are the component taxa of these clades.

I don't see any advantage to erecting this bewildering array of clades, 
with all the undecipherable vocabulary that goes along with it, and the 
interminable debates over what is in each clade.  Maniraptor, for 
example, is an unnecessary term, because we already had the same concept 
in saying that birds have ancestors among theropod dinosaurs.  We have 
always tried to identify the specific characters that diagnose birds and 
to see what their ancestors are.  What's the difference?  Maniraptor 
simply excludes ornithomimes, and puts a limit on how far back we want to 
go in theropods to be talking about an ancestor in this context (e.g., to 
the divergence between ornithomimes and the theropod group that went on 
to produce birds).  T. H. Huxley hypothesized the theropod bird 
connection in 1869, and nothing has been discovered in the meantime to 
disprove it or to require a different phrasing other than development of 
a new technique for assessing evolutionary relationships.  Pardon a 
cliche again, but it seems that the tail is wagging the dog.

Of course, messy debates ensued over the limits and content of 
conventionally-recognized taxa.  But now we have messy debates over 
phylogenetic taxa, and these are largely the result of not having learned 
from experience, of not taking the time and care to erect a new system 
that might help avoid such messy debates.  It can't be justified on the 
grounds that since there were messy debates in the old system, it's OK to 
have messy debates in the new system.  We had a chance, and maybe there 
is still a chance, to make improvements for a new system.

Maybe start by adopting a defined procedure for characterizing clades, 
like node-based.  Node-based would probably have the least disagreement 
with earlier taxonomic concepts and hypotheses of descent, and that's 
what I think we want.  (We shouldn't throw the baby out with the bath 
water!)  Don't name every clade--the proliferation of names may 
ultimately produce a structure as as complex as the tree of life itself 
(as G. O. has pointed out).  The whole superstructure will get bogged 
down by its own nomenclatorial complexity, to say nothing of the 
background chaos caused by the inevitable disagreements over diagnostic 
characters and clade "definition."

Phylogenetic taxonomy also leads to absurdities such as the Tetrapoda not 
including all animals with four legs. Now, just stop and think about that 
objectively!  That simply won't play in Peoria, and if it doesn't, we 
could all be in trouble.  Also, as I said previously, any Peorian can see 
that birds aren't dinosaurs.  At the same time, Peorians can readily 
accept that birds descended from dinosaurs by adopting a unique lifestyle 
on the basis of several unique physiological and anatomical traits that 
made such a lifestyle possible.  Since birds are such unique animals, 
there is nothing wrong with emphasizing that uniqueness.  

Now, that said, would it surprise anyone to know that I demonstrate the 
reasoning used to conclude that birds are dinosaurs in my class?  I 
supportively explain how cladistic works in the beginning of the 
semester.  I use it in other contexts, but then I really drive it home in 
discussing birds.  They learn about cladistics, they are convinced, and 
they enjoy the whole discussion.  Finally, none of this in any way 
obviates the opinions and complaints about PT I expressed above and 
before.

Perhaps I suffer from dual personality syndrome.


*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu