Paraphyly is real (and inevitable)

Thomas DiBenedetto tdib at OCEANCONSERVANCY.ORG
Mon Jan 14 13:45:27 CST 2002

-----Original Message-----
From: Ken Kinman
... If you think about it long enough, it seems clear to me
that paraphyly is not only real, natural, and "scientific"----even more than
that, paraphyly is INEVITABLE for evolution to continue.
Well, I have thought about it long enough, and it seems clear to me that you
are completely wrong. But I am glad you raise this argument, because it does
go to the roots of some issues. It seems to me that you are confusing the
concept of a taxon and the rank that some particular taxa are assigned -
most importantly the rank "species". The term "species" in systematics is a
rank applied to empirical taxa, from its Greek roots wherein it is defined
in distinction to genera - the particular and the general if you will. I
think that we both agree that a particular taxon, a species, may divide at
some time, so that a taxonimist who revists the situation after this event
may percieve two taxa, two species. How do we conceive of this situation in
a historical sense, and what type of words, concepts, ideas do we use to
accurately represent it?
You speak of a "mother species" paraphyletically giving rise to daugher
species - and you claim that if this didnt happen, then evolution wouldnt
happen. Clearly evolution does happen, so my problem is with your
conceptualization. I would say that a "mother taxon", ranked as a species (a
terminal branch in the lineage system) has divided, and that this taxon is
now no longer to be ranked as a species - it is now no longer a terminal
branch in the lineage system, but is a complex, diversified taxon - i.e. a
higher taxon. If we had given that mother taxon a name, for instance if we
had called it the species Mammalia, then we would now recognize that
Mammalia is a higher taxon for it includes two descendant species. Surely
you recognize that monotremes and therians are mammals, don't you? And that
humans are mammals as well, no? Humans are sapiens, are homo, are primates,
are mammals, are amniotes, osteichthyans, vertebrates, metazoans, animals,
eukaryotes, are part of life - all at the same time. Do you disagree with
this:? Is Eukaryota paraphyletic because humans evolved, or other
divergences occured? Terminal taxa, species, are part of all of the taxa
that their ancestors were a part of. Nothing that could ever happen in human
evolution could make humans part of Plantae, nor could anything make them
not part of Animalia, for this is our history.
The problem with your conceptualization is that it does not allow you to
recognize these facts - that an undivided lineage branch (a terminal taxon -
species), does not go out of existence when it does divide - it simply
divides, and therby becomes more diverse, in short - it evolves. It is only
because you refer to your mother taxon as a mother species that you have
difficulty realizing that the mother taxon persists, it is simply a more
complex taxon. It is, if you will, bumped up to a higher level in our
hierarchical system in which we refer to more complex lineage systems as
"higher taxa".  By calling it a "mother species", and then calling its
daughters "species", you necessarily have to claim that the daughters are
somehow removed from the mother taxon, rendering the mother paraphyletic.
But this is merely an artifact of your conceptualization.
The daugters are speces level taxa, and they are also part of the maternal
higher taxon. The maternal higher taxon is a complex higher taxon,
consisting of all those critters that were alive in the past (when the
maternal taxon was undivided), and all the critters that are alive in the
two daughter species today. The maternal higher taxon is not in any sense
paraphyletic. It is only if you fail to recognize its current complex
nature, and continue to refer to it as a "species" and then arbitratily cut
off its living descendants in other "species", that your conceptualization
becomes paraphyletic.
The maternal taxon, viewed in isolation from its descendants is an artifical
construct, for there is a continuous connection of descent between the
critters formerly alive in the undivided taxon and those alive in both of
the descendant taxa. This may bring us to the question of how one can
accurately divide up the overall lineage system (cut nature at its joints).
To me it seems clear - all animals are part of Animalia for there is an
unbroken chain of descent to the original animal, all reptiles are part of
Reptilia (and this  must include birds) for the same reason, etc etc. A new
historical phenomenon comes into being when some critters go off and begin a
novel descent chain - this doesnt remove them from their own history, but it
starts an additional descent history that is different from their sisters on
the other side of the valley - and so we recognize a new lineage branch, a
new taxon. At first it is ranked as a species, but if it diverges in the
future, then it will be accorded a higher rank. Taxa dont end, they dont
have a cutoff point unless and until every last descendant critter dies -
then the taxon is extinct. Individual organisms are part of many higher
taxa, which is  their inheritance in the overall system of descent. These
lineage branches are real, or at least that is an assumption that we choose
to make, You are free to recognize them as we infer them to be -
historically integrated systems of descent, or you can cut through the
natural lines of descent and recognize artifical groupings - paraphyletic
groups. But that is your decision - the notion that paraphyletic groups are
natural phenomena is absurd.
I honestly dont see how your conceptualiztions can in any way offer a
vocabulary that makes any sense in light of our understanding of evolution.
Perhaps the root of your problem is that you really havent figured out how
to integrate the notion of change over time into your conceptualization of
systematic categories.
Read My Lips:  Clades are real, but "sister clades" are a convention.
I dont understand your point here. If a lineage divides into two daughter
lineages, then the daughters are sisters. What logical or conceptual system
are you employing that can see this  as a mere convention?

Tom DiBenedetto

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