Comments to Cladistics/Eclecticism, part 2

Fri Feb 8 18:19:24 CST 2002

(Taxacom allows maximally 250 lines per email, so I
had to cut up my email ... sorry. Here's part 2:

4. Arbitrariness / subjectivity
Apparently, we all agree that in deriving
classifications, Eclecticists and Cladists both start
by making a cladogram. Eclecticists then delimit
holophyletic and paraphyletic groups as taxa, while
cladists recognize only holophyletic groups as taxa.

        If you give a cladogram to a number of cladists, they
all will delimit the same groups. They will not
disagree. The group-formation in cladistic
classification is non-arbitrary and objective. (In
theory, all groups should get names, but in practice,
this is usually not done. So the cladists might
disagree on which groups to name and on how to name
them, but that is an unimportant issue  the
composition of the groups would always agree and
thats the important issue. As we say in German:
Namen sind Schall und Rauch.) The group formation is
given by the cladogram. Once you have a cladogram, the
group delimitation is completely unambiguous,
objective and non-arbitrary. And this is the beauty of
cladistic classification.

        If you give a cladogram to a number of evolutionary
taxonomists, they will come up with different,
incongruent classifications. You said that you look
for the greatest gap, that is which groups are
separated by the largest number of character
transformations. But in reality, these gaps are
artificial which have been produced only by
extinction. Evolution proceeds in little steps. There
were no gaps in reality. You, Ken, noticed yourself,
how it gets more and more difficult to draw a line
between reptiles and birds the  more fossils are
being discovered. You are arguing where the most
important gap would be. Yesterday you drew the line
there, today you say: oh, no, wait, I found a better
gap, birds start here. Discover a few more fossils
and you wont find a gap at all. This is why an
eclecticists group formation is subjective, arbitrary
and artificial. It is artificial because the gaps
are artificial, and it is subjective and arbitrary
because the same cladogram will be paritioned into
different groups by different eclecticists.

        Another example. You might be very surprised to hear,
that I -- a strict cladist -- am working on a
paraphyletic group. My study group is lower
hymenopterans = non-apocritan hymenopterans = sawflies
=  Symphyta. (I never use the last term without
quotation marks, which cladists use as ex-group
markers (?)  for paraphyletic groups.) (Of course, I
never do my cladistic analyses without including some
higher Hymenoptera as well.) Anyway, of the symphytan
lineages, Orussidae is believed to be the sister taxon
of Apocrita. Together they form the Vespina. The
sister group of Vespina is Xiphydriidae. There are
many synapomorphies for Orussidae+Apocrita and many
synapomorphies for Apocrita. Two significant gaps for
an eclecticist.

If you give a cladogram of Hymenoptera to three
eclecticists and ask them to classify them, you might
get three answers, I believe:
1. Hymenoptera are Symphyta plus Apocrita, because the
most important change in the evolution of Hymenoptera
is the development of the wasp-waist in the stem
species of the Apocrita.
2. Hymenoptera are Symphyta minus Orussidae plus
Vespina, because the most important change in the
evolution of Hymenoptera is the evolution of
parasitism in the stem species of Vespina. (Orussids
are the only parasitoids among sawflies.)
3. Hymenoptera are Symphyta minus Orussidae plus
Orussidae plus Apocrita, because both these gaps are
important.

Furthermore: I see a huge gap between fishes and
tetrapods. Do you, Ken, classify Vertebrata as Pisces
plus Tetrapoda? If not, why not?

By the way: its hard or impossible for me not to talk
about sawflies at all, but Im perfectly happy with
calling them sawflies or basal hymenopterans or
non-apocritan hymenopterans. I can understand that you
want to talk about reptiles, but cant we leave it at
reptiles and not Reptilia? I think in one of your last
posts you said you might be able to compromise in this
way. Please consider this. A classification that
contains Reptilia is an unscientific classification
because it is based on subjective, arbitrary decisions
which in turn are based on artificial gaps in the
fossil record.

Also, reptiles and sawflies might be okay to use for
non-biologists, I guess. [As someone put it (I forgot
who): the best classification for cookbooks is the
classification of cookbooks. (Game, seafood, fish.)]
Of course, other cladists are more strict in this
matter.

5. Are monophyletic and paraphyletic groups equally
natural?
The species that live today are isolated
reproductively from each other. Within one time
section, they can be separated. But back in time, they
are all connected somewhere. Life on earth is one big
continuum. Any cut in this continuum exists only in
the human mind. Species are just concepts. Anyway, the
cuts in this continuum can be made based on real
events, that is the branching events. But since time
goes in only one direction, any such cut can delimit
only a group of those individuals that appeared after
that cut. (Pierre Deleport posted something on this
topic yesterday where he talked about backwards and
upwards classification.) The branching events are real
events and they naturally divide up the live on this
planet in natural entities, i.e. monophyletic groups.
If you use a cut to delimit the taxa that where there
after the cut on one hand and before the cut on the
other hand, one of them is artificial.
Look at the following analogy: take one bacterium, put
it in dish 1 and let it divide a number of times.

You get a clone, clone 1. I think we would all agree
that this is a natural group. Now take one bacterium
from dish 1, put it in dish 2 and let it divide to get
another clone, clone 2, which is also a natural group.
Now, the bacteria in dish 1 AND dish 2 TOGETHER are
also a natural group because they are all the
descendants of the first bacterium that you took.
Clone 2 is a subclone of clone 1, i.e. clone 2 is part
of clone 1. However, the bacteria that are now in dish
1 are not a natural group, because you artificially
excluded some of the descendants of the first
bacteria.

Even if the one bacterium that you took out of dish 1
looked somehow different than those left behind
(because it has a mutation), so that all the bacteria
in dish 2 would look different from those in dish 1,
while those in dish 1 remain perfect copies of the
first bacterium, the group of bacteria in dish 1 would
still not be a natural group!!! Even if they were more
SIMILAR to eachother than to the bacteria in dish 2!!!
The bacteria in dish 1 are then nothing but a phenetic
group!

        If you think now of every bacterium (in this analogy)
as a species, a paraphyletic group of species is
equivalent to the group of bacteria in dish 1. A
morphologically distinguishable, recognizable phenetic
group, yes, but not natural !

        (By the way: dont reply with the argument that the
group in dish 1 is artificial only because it was
created by human intervention. This has nothing to do
with it.)

This is why upward classification is natural, but
backward classification is not. Separating
Sauropsida into Aves and Reptilia is just as
artificial as separating Animalia into Vertebrata and
Invertebrata or Vertebrata into Tetrapoda and Pisces.
More precisely: Aves, Vertebrata and Tetrapoda are
natural entities, Reptilia, Invertebrate and Pisces
are artificial.

        You can make such an artificial classification, but
its not scientific because it is based on arbitrary
decisions, on human taste, and not on natural
entities.

to be continued....

=====
New journal: ODE - Organisms, Diversity and Evolution
by the Gesellschaft für Biologische Systematik.
http://www.urbanfischer.de/journals/ode

Susanne Schulmeister
Institute of Zoology and Anthropology
University of Göttingen, Germany

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