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Re: Clade II



At 08:21 PM 1/22/97 +0000, gautam@majumdar.demon.co.uk wrote:
>Jeffrey Martz <martz@holly.ColoState.EDU> wrote :
>>
>>THERE ARE NO "REAL" OR "NATURAL" GROUPS
>>     
>This is absolutely right. You classify a group (of anything) for a purpose 
>and select your criteria accordingly. Each such classification is valid in 
>its own context.

Indeed.  However, the goal of modern taxonomy is to apply labels to the
"tree of life": the real, historical branching pattern of lineages through
time.  In such a task, not all tools are equally effective.

>Cladistics is fine for phylogenetic classification of the organisms. If on 
>the other hand you are out hunting with a bow and an arrow, you might 
>like to classify the animals according to the thickness of their skin. In that 
>context it is a perfectly valid and better classification than cladistics.

However, if your goal is unravelling the tree of life...

Also, I would like to point out to Martz and others (in the references noted
before by Wagner, and indeed the vast body of recent literature on the
nature of taxa):

Under many species concepts accepted by cladists, species are not clades.
They are a different kind of entity, just as organisms are not genes.
Clades are composed of species, but species are not composed of clades.  As
such, they do not follow the rules of monophyly.

As to whether we should allow ICZN rules to dicate phylogenetic
reconstruction is a matter of debate.  Some systemicists would be happy to
ignore the genus concept altogether, and in fact go so far as to not require
changing the "generic" name of a species if it is discovered that (say) Homo
habilis turns out to share a more recent common ancestor with Gorilla
gorilla than with Homo sapiens.  I would not go that far.

However, I would not say that, because the way ICZN requires all species to
have a generic name, that we must therefor accept all paraphyletic taxa, either.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877