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RE: Defending grades (Was: Re: Archaeopteryx (rant))



Daniel Grossberg (grossber@grinnell.edu) wrote:

<All my original post was saying is that ancestral line cannot be the only
 defining characteristic of a cladogram.>

  The whole point of a cladogram is to show a set of ideas in how some
animals are related to one another. There are different ways to do this.
In Phylogenetic Taxonomy, the best way to represent a cladogram is one
where all taxa form sets of nodes and stems, and an ever increasing change
from an ancestral state; this latter clause is also in fact the goal of
most other cladograms. _How_ they descend, what are the barriers between
the ancestors and the descendants, and names we give any parts of these
trees, all depend on separate philosophy. What Daniel was arguing against,
however, was that it is possible to have a paraphyletic assembly, where
any group can exclude its ancestor. Question is ... why? What usefulness
does this bring to quite human-ly and arbitrarily exclude an ancestor from
a lineage? It is not hard to simply define a starting point and name it,
then let that name stand for ALL included taxa; there will be no end until
the lineage stops propigating species. The lineage being infinite,
extending to the first microbial life to the present and into the future
incarnations of any organisms, this may be daunting to some who would like
their clade or rank names to be employed only for a certain number or
finite limit of organisms, or a type of this, a typology that has been
criticized _ad nauseam_ on this list for nearly a decade, and in press for
MUCH longer.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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