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Re: Clade II



At 10:55 AM 1/27/97 -0700, Jeff Martz wrote (even though he said he wouldn't :)
>     BINGO!!  Does phylogenetic taxonomy name species?  If so, then
>paraphyletic groups apparantly DO have a place in taxonomy!  
        Actually, as I recall, it does not, because you they are
paraphyletic, and because it is damned hard to name something as "the most
recent common ancestor of Specimen THX-1138 and... uh... it's the only
specimen..."

>THEN you sketch in
>macroevolutionary paraphyletic groups.  The last step, but by no means the
>least important.  The framework that paraphyletic taxa are draped on
>SHOULD be phylogentic.
        As I just wrote, this leads to confusion over which taxa are
actually monophyletic.  you yourself have pointed out that cladists use
paraphyletic groups of convenience.  Why can't you leave it at that?  Why do
your paraphyletic groups HAVE to be taxa?

>>         I've said it before, I'll say it again, why would you wish to
>> obscure the most confusing aspect of evolution behind those aspects which
>> are more readily discernable?  If any two-year old can tell the difference
>> between a bird and a non-avain dinosaur, why should we include this at the
>> risk of obscuring their theorised relationships?
>
>      The same differences are used to IDENTIFY Aves as a monophyletic
>clade.
        No, they are used to support the inclusion of certain animals in a
clade which has already been defined (except, of course, for those animals
included in the definition (ie. Neornithes and _Archaeopteryx_).  Aves is
identified as monophyletic by being defined that way (as George Olshevsky
has recently gone to extremes to point out).

>A smart two year old could understand common descent.
        But can he tell that an Aardvark, a gliptodont, a staganolepidid
(aetosaur), and a nodosaur are not related?  Yes, if you tell him.  Narrow
the focus.  Can he comprehend that your "dinosaur" and your "bird" are
really staggeringly closely related, indeed that some dinosaurs are more
closely related to birds than others, if you insist on seperating the two
with paraphyletic distinction?  As I have repeatedly tried to point out on
this list, drawing artificial parapyletic taxa confuses issues.

>Perhaps a
>special suffix could be used to designate paraphyletic groups, in order to
>distinguish them from monophyletic clades (presumably the classical
>Linnean suffixes).
        Eyew!  Recall that paraphyletic taxa are gross for many reasons
other than just that one couldn't tell the difference.  Yeach!  Please don't
suggest this again, it's grody.  :)

>The issue is whether or not groups are easy to recognize       
        Why?  Taxonomy is not a field classification.  Why should we make
things easier to classify, when making them so reduces the clarity of the
information contained in that classification.

>    So does ancestry: the OTHER way.  How would a group based on "an
>organism and all its ancestors", a paraphyletic group, be less real then
>one based on an organism and all its descendants"?
        I really honestly don't know. I'd venture to guess that it isn't
because it doesn't include the decendants of those ancestors.  But it may
just be real.  On the other hand, it certainly wouldn't be all that useful.
Dr. Holtz, you wouldn't happen to know?

        Wagner
+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
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