Cladistics and "Eclecticism"
Pierre.Deleporte at UNIV-RENNES1.FR
Thu Feb 7 18:11:35 CST 2002
At 10:44 06/02/2002 +0100, Zdenek Skala wrote:
>the current paraphyly/holophyly discussion seems to point constantly to
>Is the amount of character change (better of character state difference in
>an operational context) a core subject of systematics?
> there were several requests within the current thread for criteria used
> by eclecticists for delimiting paraphyletic taxa. I would like to repeat
> again that this is *not* the sole problem of paraphyletic taxa; the same
> problem arises when delimiting the holophyletic taxa. For some of
> cladists, the answer seems to be that limits of taxa are arbitrary
> decisions (practical, not scientific) and hence there is no problem. I
> would disagree and hope that many cladists will, too. If the system of
> taxa would be an arbitrary split of a cladogram, systematics is losing
> its merit IMO - the phylogeny was originally intended to be a *tool* how
> to naturally explain and summarize the organisms' diversity!
Once you have the data matrix and the tree, you have this tool available
for science. Naming groups is a question of conventions for efficient
>Hence, let's discuss the criteria of the taxa limits and leave for a
>moment if these limits will be used in a holophyletic or paraphyletic
> I personally believe that the amount of apomorphies at the respective
> nodes gives a good starting point for taxa-limits optimization process.
Yes, if you need to deal with such "well-separated groups" for some
reasons, then you will like to name them.
Now this is not the only possible situation. As a student of social
evolution, I could like to name a clade characterised by a synapomorphy in
this respect (social organisation type Y), and also to name a subclade
characterized by a further change (e.g. reversal to type X), whatever the
total amount of changes in other respects.
Thus the number of changes in different characters is not the only possible
criterion, and characters of interest matter (by definition, they are "of
interest" for the specialist, and differ according to questions at stake...).
This is why naming some taxa (not all taxa) is a practical question, and
neither "natural", nor properly "scientific" in any non-trivial way.
"Optimization" in this field depends on the centers of interests of the
users: which groups we need to name for some concerns (quantitative or
(Naming all taxa is not an issue here, it boils down to "redrawing" the
complete tree with words. Maybe largely a waste of time)...
>There was made also a separate point that paraphyletic taxa having
>"origin" and "end" need to have "more arbitrariness" to be defined than
>the holophyletic taxa.
I can recognise one of my posts on this topic.
> I believe this is not true: let's imagine a pectinate cladogram of
> species A,B,C,D,E where clade A+B is supported by 5 synapomorphies, A+B+C
> by 2 syn., A+B+C+D by 10 syn. and the entire group by 12 syn. Eclecticist
> will split the cladogram into, say "genera" A+B, C+D and E and families
> A+B+C+D and E.
You mean that two significant gaps are retained for naming: 5 changes and
Besides the trivial terminals and complete clade (ABCDE), note that
restituting complete phylogenetic information requires here 3 genera and
two families, thus 5 names,
plus complementary information (e.g. Kinman markers) indicating the
paraphyletic nature of C+D and where do A+B belong,
plus extra marking (or an ordering system) indicating the hierarchical
nesting of ABC inside ABCD.
> Cladists, I believe, will use taxa A+B, C, D, E and more inclusive taxa
> A+B+C+D and A+B+C+D+E.
You mean that they will possibly name only two clades (besides the trivial
five terminals and complete clade ABCDE), retaining 5 and 10 as significant
Besides the trivial terminals and complete clade (ABCDE), for fair
comaprison with the above eclectic system, note that for restituting
complete phylogenetic information, 3 names are required (AB, ABC and ABCD),
with markers (or an ordering system) indicating their hierarchical nesting.
To be complete, naming the paraphyletic group of interest C+D requires
several words, but no extra name:
C+D is "non-AB ABCDs".
> As you can see, the number of taxa limits is the same or lower in the
> eclectic solution (limits B|C, D|E) - the difference is only in the level
> at which they are used. Hence, the "amount of arbitrariness" is the same
> in cladistic solutions as in the eclectic ones - at best.
I don't see at all that the number of limits is lower. It is 5 and 10
changes judged "significant gap for naming" in both cases (and besides this
cladistics clearly require fewer names in this case).
Anyway my point on this topic was not at all the criterion for "significant
gaps" in itself (same problem in the two cases as you notice quite well, no
more "significant" or "natural", no less). I meant that additional
arbitrariness is introduced by the requirement of deciding "when to look at
phylogeny backwards", and not always "upwards" :
The cladist has a unique criterion: clades. He(she) may add the criterion
"significant gaps" if he refuses to name all the clades. Here he decides to
consider "more than 4 changes" as significant (qualitative criterion
possible, see above).
-------End of decisions.--------
Consequently, he names clades A+B (supported by 5 changes), and A+B+C+D
(supported by 10 changes).
Now, the eclecticist has two incompatible criteria: clades, and possibly
grades. He may add "significant gaps" if he refuses to name all the clades
or grades. Here he decides to consider "more than 4 changes" as
significant, just like the cladist (and qualitative criteria seem to be
******But this is NOT the end of decisions.******
He has now to decide when he will look at the tree "upwards" versus
Here he decides to look at the tree "upwards" at the 10-changes gap, but
downwards at the 5-changes gap
(strange enough, but this is your example).
---------End of decisions.---------
Consequently, he names clades A+B (supported by 5 changes), A+B+C+D
(supported by 10 changes), and grade C+D (supported by 5 changes at the
"upper bound"? Or supported by its insertion between the 10- an 5-changes
It simply seems obvious to me that supplementary decisions are involved in
the eclectic approach, and that they are logically necessitated by the
initial choice of implementing two incompatible criteria at the same time
for the unique task of naming.
The supplementary decision concerns when to stop applying one criterion in
favor of the other, which is clearly not a concern for the cladistic system.
If we add the possibility that no universal priority rule is presently
available for deciding between the two eclectic criteria, this makes a
pretty good lot of supplementary room for arbitrariness in applying naming
Now the good question seems to be: does it matter at all and why? What is
gained, what is lost, and are there more coherent alternative solutions for
conveying complex information (markers...)? And the answer should be linked
to: what naming conventions do we need for smart communication?
Reaching common agreement between scientists (hence at least more
stability) seems an issue, and minimizing abitrariness may matter in this
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