[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Paraphyly and sister taxa




Jeffrey,
This is why the Kinman System "explicitly" states paraphyly whenever possible. The problem with strict "cladifications" is that most no longer even implicitly indicate paraphyly, and many cladists actually believe that an ancestral species goes extinct (or ceases to exist) when it splits into two "sister" species.
The latter concept is only a Hennigian "convention", and in reality almost all speciation events are actually paraphyletic mother species budding to give rise to a daughter species. The mother species survives the speciation essentially unchanged. Such Hennigian conventions are fine until they begin to be taught as though they are real evolutionary processes.
Unfortunately, increasing numbers of cladistically trained biologists are not taught, or do not understand, that this is a convention rather than a real evolutionary event. The Kinman System attempts to counter this by making it formally more explicit, but not so much so that it negates the positive aspects of cladistic predictivity.
--------Ken Kinman
*********************************************************
From: "Jeffrey Martz" <jeffmartz@earthlink.net>
Reply-To: jeffmartz@earthlink.net
To: <NJPharris@aol.com>, "Dinosaur" <dinosaur@usc.edu>
Subject: Paraphyly and sister taxa (was Re: AMARGASAURUS SATTLERI)
Date: Sun, 3 Sep 2000 15:04:22 -0500


Dinogeorge wrote:
< It's difficult (though not impossible) to avoid paraphyletic genera in
this
<situation. If D. sattleri and A. cazaui are sister groups, then D sattleri
> could indeed be placed in the genus Amargasaurus. But then what happens to
> the common ancestor of Dicraeosaurus and Amargasaurus?



Nick P. wrote... >Let's worry about that when we dig it up and recognize it as such, OK? >We only have to name and classify the individuals available for study >(thank God!).


But the same problem applies to ALL sister taxa in any given cladogram.
If you have two different taxa, "A" and "B", there are three and only three
possible idenities for their common ancestor:
1. The common ancestor is the same taxon as "A", in which case "A" is
paraphyletic with regard to "B".
2. The common ancestor is the same as "B", in which case "B" is paraphyletic
with regard to "A".
3. The common ancestor is neither "A" or "B", in which case it is DOUBLY
paraphyletic.
Paraphyly is implicit at EVERY NODE where the sister taxa are not
identical, which means at every node except where individual specimens
assigned to the same genus and species are sister taxa. Unless we are
willing to place every single organism in the same genus and species, there
is no possible system of taxonomy that can eliminate paraphyly. Taxonomy is
useless WITHOUT implicit paraphyly.


LNJ
*****************************************************************
Outlawing drugs in order to solve the drug problem is much like outlawing
sex in order to win the war against AIDS.
-Ronald Siegal

No matter how far you have gone on the wrong road, turn back.
-Turkish proverb
*****************************************************************
Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
3002 4th St., Apt. C26
Lubbock, TX 79415
(806) 747-7910
http://illustrations.homestead.com/Illustration.html
Now featuring VERTEBRATE drawings!!
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

Share information about yourself, create your own public profile at http://profiles.msn.com.