Characters.

John Grehan jgrehan at SCIENCEBUFF.ORG
Fri Jun 18 09:38:13 CDT 2004


> From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU] On
> Behalf Of Richard Jensen
> 
> This reply is proof that you are choosing to ignore a fundamental fact
of
> taxonomic analysis: characters do not represent overall similarity.
> Overall
> similarity is a function of the way the characters are analyzed and
has
> nothing to do with the methods by which characters are defined or
coded.

I think I see your perspective. I could restate my view to say that
characters that are not limited to potential apomorphies through
individual evaluation will result in analysis that represents overall
similarity rather than necessarily phylogenetic relationship.


> As
> several of us have repeatedly emphasized, the same data matrix my be
used
> to
> construct either phenetic (i.e., overall similarity) or cladistic
(i.e.,
> patterns of nested synapomorphies) relationships.  

Yes one can apply different alogorithms, but characters that are not
limited to predicted apmorphies will not result in a cladistic phylogeny
no matter that a cladistic algorithm is applied since one cannot
construct patterns of nested synapomorphies from characters that are of
themselves not apomorphies even though they may be presented as if they
are.

This is something you
> just have to accept (sort of like gravity) - you can't ignore it or
> explain
> it away by special pleading or ignorance.

Actually I don't have to accept anything(and neither do you of
course)any more than I have to accept Darwinism simply because nearly
everyone practices it. In this case I don't accept your assertion
because I do not see it working in what I see as the real world of
cladistics. Yes I might be wrong, and so may you.
> 
> I will admit that I may be overlooking something very fundamental.
So,
> please explain to me how a character (or a set of characters) can
> "represent
> overall similarity."

I doubt anything fundamental is being overlooked - just a reflection of
a different history of exposure to the subject.

When one looks at all characters altogether one might, for example, see
that humans and chimpanzees have a greater overall similarity (e.g in
body proportions, short body hair)to each other than either with the
orangutan. This is overall similiarity includes plesiomorphic states
that can actually be found in other primate taxa so they are not a
necessary indicator of immediate phylogenetic relalationship. Similarly,
orangutans have been rejected as being closely related because they are
so different (I had one prominent primate paleontologist present this
argument)which is a consequence of their autapomorphies such as cheek
pads and vocal sacks as well as other characters which also may
represent other plesiomorphies or possibly parallelism (such as the long
arms). 

So one may take the total number of characters shared between humans and
great apes and do a 'cladistic' analysis by rooting with some other
taxon (actually a case where this was done recently using the orangutan
as the outgroup because that assignment was beyond question) and make a
cladogram out of it. But that cladogram does not represent a nested set
of synapomorphies even though the characters may be treated as if they
were. It seems to me it would be a case of garbage in, garbage out.

John Grehan




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