[Taxacom] Phylogenetic Classification?

[Kenneth Kinman]

Hi John,
         Paraphyletic species are very common among both animals and
plants.  Homo erectus is the paraphyletic mother species of our own
species Homo sapiens.  I simply classify it as the species Homo erectus%
(the % symbol indicates it's paraphyletic), and then divide it into
subspecies plus a {{Homo sapiens}} marker showing which of those
subspecies it probably evolved from.     
       In a phylogenetic analysis of species, the cladogram would most
likely show them as sister species, and I suspect strict cladists most
often simply don't realize the paraphyly exists and or don't dig enough
to find out.  When they do recognize the paraphyly, I believe that they
sometimes apply the name "metaspecies" to the paraphyletic mother
species.  I have no problem with that if they don't want to call it
paraphyletic and having a term metaspecies would make it more palatable.
However, I do have a problem with strict cladists who don't even like
metaspecies and want to split up this mother species into additional
species just to solve the unwanted paraphyly.  The phylogenetic species
concept thus recognizes a lot more species than an evolutionary species
concept.  At least such splitting seems to be a lot more common than
their other alternative (lumping the daughter species into the mother
species).  I'm not sure what strict cladists plan to do with Homo
erectus, but I suspect that they would advocate splitting it up.    
        ----------Ken Kinman
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John Boggan wrote:
Maybe this has already come up but I don't have the time or patience to
wade through all the discussion in the archives.  How are paraphyletic
species to be treated in strictly cladistic classifications?  I don't
know about animals, but in plants paraphyletic species are probably
quite common, i.e., one or more morphologically distinct and
reproductively isolated species have been derived from a common and
widespread ancestral species that still exists.  Recognizing those
derived species makes the ancestral species paraphyletic, but it is
still a species (or is it?) in that it consists of interbreeding
populations that are united by gene flow while reproductively isolated
from their relatives (including the descendant species).  Should the
derivative species be synonymized under the ancestral species?  And if
not, what are the phylogenetic implications of the subsequent history of
these two taxa, one monophyletic but the other not? 
 
Most molecular phylogenies will not reveal this problem (or at best only
hint at it) because they sample only one individual of each species. But
taking the problem to a reasonable extreme, it's theoretically possible
for a single founding individual of a species, landing on an island, to
undergo an evolutionary radiation and give rise to numerous new genera
and species even while the ancestral species still exists on the
mainland, remaining more or less unchanged.  In practice, extinction of
populations and entire species probably saves us from this problem. But
if it could be shown that the founding individual (and thus all its
descendants) was more closely related to one population of the ancestral
species than another, the classification of that group could get awfully
messy...