[Taxacom] A Cladist is a systematist who seeks a natural classification

Sat Apr 7 00:10:40 CDT 2018

Since there are at various times some strong opinions on cladistics and on
natural classification I have pasted below the text of a recent article
that might be of interest to some (some typos may have crept in during the
copy/paste).

Biol Philos (2018) 33:10
https://doi.org/10.1007/s10539-018-9621-7

David M. Williams & Malte C. Ebach

A Cladist is a systematist who seeks a natural classifcation: some comments
on Quinn (2017)

Abstract. In response to Quinn (Biol Philos, 2017.
https://doi.org/10.1007/s1053
9-017-9577-z) we identify cladistics to be about natural classifications
and their
discovery and thereby propose to add an eighth cladistic defnition to
Quinn’s list,
namely the systematist who seeks to discover natural classifications,
regardless of their affiliation, theoretical or methodological
justifications.

Derived from various permutations of phylogeny, biology, philosophy,
methodology, sociology, loyalty etc., Aleta Quinn recently proposed “seven
specific definitions that capture distinct contemporary uses” of cladistics
(Quinn 2017, p. 1). Our own efforts, based on the same criteria, yielded a
further seven, which we do not intend to bore our readers with here. We are
sure more could be found and more people could be found who
subscribe/correspond to them. Suffice to say, one might find definitions
for anything—and in any case, Quinn was clear about her motives:“I do not
intend to classify individuals, ideas, or research programs. Rather, I
clarify distinct things that speakers mean by the term ‘cladist’” (Quinn
2017, p. 1). Depending on one’s outlook—philosopher, historian, biologist,
even sociologist (Hull 1988)—the definitions might help progress their
subject. As biologists, we found much to think about but rather than
dissecting the minutiae, we seek to clarify by attempting to simplify.
We need first to dispense with one misconception. Quinn draws upon a
commonly preconceived notion, namely that systematics requires evolution as
a prior condition:1

“What that theoretical foundation may have been [in reference to de
Candolle’s
view on characters] is not relevant to my points about contemporary
systematics,
whose conceptual framework presupposes the concept of evolution” (Quinn
2017, footnote 11).

Consider the concept of a cladogram, which everyone might agree is a
branching diagram commonly included as part of the results of a cladistic
analysis. One might derive from this diagram which taxon is more closely
related to itself than to any other. One might explain this relationship by
common descent. The cladogram, however, need not be constructed with any
evolutionary assumptions in mind; rather, the evolutionary assumptions
serve to explain why one taxon is more closely related to itself than any
other.

The search for a natural classifcation was established prior to the
adoption of
any theory of evolution. In fact Augustin P. de Candolle’s had a great deal
to say
on the matter, especially the differences between natural and artificial
classifications (Candolle 1913). But de Candolle was working some time ago,
so what, if anything, might be his relevance today? Methods of systematics
change as time passes. But all methods fnd cladograms, in the sense that
the results yield sets of relationships, either as a branching diagram or
as a written classification. Regardless of method, which of these
relationships might be considered to reflect something that actually
exists, rather than a product (an artefact) of the method? How can any
method achieve that without knowing the answer beforehand? Obviously it
can’t. One might play around with simulation studies to judge the
performance of any suite of methods, or one might delve into philosophy to
create justification, but in the court of last resort all that remains are
sets of cladograms that either agree or disagree to a greater or lesser
extent in terms of common relationships found. That is, they agree in the
cladistic parameter, the relationships specified—that the signal to noise
ratio is working in our favour, as is evident from classifications of the
past. Here we might argue that natural classification is the result derived
from several cladograms, regardless as to how they were arrived at;
artificial classifications are derived from a specific method, be that
Wagner parsimony, UPGMA, maximum likelihood and so on, or from a specific
source  of data (DNA, ultrastructure, etc.), and so on. Why are these
artificial? Because a method, any method, assumes the results that are
required (the shortest tree; or the most similar taxa grouped together; or
the most similar taxa grouped together via a weighted model of character
change, etc.); for a data source, they assume those data are privileged
over other data (DNA must be the source of ‘true’ relationships, etc.).
Cladistics, in its most general sense, does not associate with any one
method, or any one data source. It applies to sets of relationships—it is
the set of relationships. This is effectively what de Candolle argued for,
and has been the basis of systematics for decades, if not centuries:

“For the last 50  years and more—even now continuing into the realm of
nomenclature—in the name of the modern and the new, Visionaries aim, as
it were, to confine the past to a dustbin of history, and to bolt and lock
the
lid upon it. As if without it, we be in some way better, even born again
more
whole-some; as if Carl Linnaeus really were among the last of the Ancients,
and not, rightly, the first of the moderns, and so related to us—of a group
inclusive of us” (Annual Review of the Linnean Society, 2001).

These words, not readily accessible, were spoken by Gareth Nelson after
receiving the Linnean Gold Medal and re-cast above as part of the 2001
Annual Review of the Linnean Society, London. Linnaeus as the first of the
moderns? Among other matters, Linnaeus spoke of the differences between
artificial and natural classification, a subject taken up and developed by
de Candolle (1913). One might cast that debate in very simple terms:
artificial classifications are found by imposition, natural classification
is discovered. Imposition implies some method or motivation to erect a
particular classification, such as a field guide or handbook for
identifying specimens—today it is more likely those would be websites, or
online interactive guides. There is nothing wrong with artificial
classifications. We both use them all the time, almost every day (
https://www.trilobites.info/;
http://naturalhistory.museumwales.ac.uk/diatoms/). But whatever merits they
have, and there are many, they
are created by acts of imposition. We ask our readers, then, if they would
consider analysis of some data with one or another statistical program, or
with one or another parsimony program, or with one or another phenetic
program, whether this is an act of imposition or an act of discovery? We
see it as an act of imposition. How could it be otherwise? Cladistics,
then, is about discovery, about finding repeating patterns,finding the same
relationships, finding relationships that are not method dependent, finding
relationships that are reflections of the world as it is:

“What, then, of cladistics in relation to the history of systematics? If
cladistics
is merely a restatement of the principles of natural classifcation, why has
cladistics been the subject of argument? I suspect that the argument is
largely
misplaced, and that the misplacement stems, as de Candolle suggests, from
confounding the goals of artifcial and natural systems” (Nelson 1979, p.
20).

For us, cladistics is about natural classifcations and their discovery, an
activity
that occurs with or without “knowledge of process”. Look in museums,
herbaria,
universities and other institutions that still hire systematists and you
will see:

Cladist (viii): A cladist is a systematist who seeks to discover natural
classifications.