LETTERS TO THE EDITORS
Cracking the Code
To the Editors:
Two items in the July-August issue addressed the PhyloCode, a system
for governing the names of biological taxa (taxonomic groups) based
on evolutionary principles. As a co-author of that document, I would
like to clarify points raised in both articles.
In her From the President message, Lynn Margulis states
that the PhyloCode uses a conceptually flawed topology of
evolutionary trees. The PhyloCode, however, is not based on
evolutionary trees but on definitions that specify the references of
taxon names in terms of common ancestry relationships. Such
definitions can be applied in the context either of trees or of more
extensively connected graphs, which are necessary to represent
evolutionary fusions. In the latter case, they result in names being
applied to partially overlapping groups. Consequently, names
governed by the PhyloCode would do a better job of representing the
symbiogenetic origins, as Dr. Margulis advocates for certain
taxa, than do the traditional taxonomic and nomenclatural
systems. As a unified code, the PhyloCode would also solve the
problem pointed out by Dr. Margulis concerning organisms that are
neither plants nor animals but have been given different names under
the traditional botanical and zoological codes.
In "Attacks on Taxonomy" (Science Observer),
Roger Harris aptly describes the controversy surrounding the
PhyloCode. He states, however, that the system of nomenclature
represented by the PhyloCode is meant to replace the system
developed by Carl von Linné (Linnaeus). The system of
nomenclature that the PhyloCode is meant to replace was developed
roughly 100 years after the time of Linnaeus and ties names strongly
to taxonomic ranks. The PhyloCode represents a return to an approach
more similar to that adopted by Linnaeus and other early naturalists
in that names are more strongly tied to taxa (now conceptualized in
evolutionary terms) than to ranks. Nevertheless, abandoning the
Linnean hierarchical ranks is not a core proposition of the
PhyloCode, which does not prohibit the use of ranks but only
replaces their function in specifying the references of names with
methods based on evolutionary principles.
Kevin de Queiroz
National Museum of Natural
History
Smithsonian Institution
Washington, D.C.
Dr. Margulis responds:
I laud Dr. de Queiroz's expertise and the PhyloCode's desire to
stabilize the names of taxa when their associated ranks change. Were
we to know common ancestry relationships among a majority of
species, definitions that specify the references of taxon names
might be properly descriptive.
However, we know very few of the estimated 30 million species of
extant organisms. Therefore, the ability to employ partially
overlapping taxonomic groups does not solve any problems of names
and ranks. Rather, it will likely generate more esoteric confusion
and grant license to those who yearn to replace groupings of messy
live beings with neatly quantifiable computer categories. For this
reason, I reiterate the need to open the acute problem of the naming
and evolutionary classification of all life to the broader research
community that Sigma Xi represents.