limb being a well known example. These observations ledhim to promote the idea of invariant morphologicalarchetypes in Nature. Darwin later coined his memorablephrase ‘descent with modification’ to explain what we nowcall ‘homologies’ (traits with shared origins) in the traits oforganisms. The accompanying sense that, somehow,Nature is limited in what it can produce, being constrainedby a few archetypes or plans, remains influential eventoday, finding life in phrases such as ‘phylogeneticconstraint’ and ‘phylogenetic inertia’.

But it is a view with little supporting empirical ortheoretical evidence. Homologies are indeed widespread,but the ability of Nature to produce new traits and torestore old ones suggests a less constrained role. Apparentconservatism in some traits could say more about theirexceptional adaptive value than about any inability toalter them: just compare the mobility of the roboticMartian rovers currently inching around the surface ofthat planet to that of just about any tetrapod. Conservedmorphologies might also reveal something about thefundamental nature and physics of our environment.

Phylogenetic–comparative studies cannot replace fos-sils as a way of understanding the processes of evolution,but they can provide an independent and complementaryview [11]. From the evidence that researchers such asCollin and Cipriani and others report, we might expect tosee many more examples in the future of the creative roleof Nature in evolution.

References

1 Gould, S.J. (1970) Dollo’s Law: irreversibility and the status ofevolutionary laws. J. Hist. Biol. 3, 189–212

2 Collin, R. and Cipriani, R. (2003) Dollo’s Law and the re-evolution ofshell coiling. Proc. R. Soc. Lond. Ser. B 270, 2551–2555

3 Ponder, W.F. and Lindberg, D.R. (1997) Towards a phylogeny ofgastropod molluscs: an analysis using morphological characters. Zool.J. Linn. Soc. 119, 83–265

4 Larget, B. and Simon, D.L. (1999) Markov chain Monte Carloalgorithms for the Bayesian analysis of phylogenetic trees. Mol.Biol. Evol. 16, 750–759

5 Hoagland, K.E. (1977) Systematic review of fossil and recent Crepidulaand discussion of the evolution of the Calyptraeidae. Malacologia 16,353–420

6 Pagel, M. (1999) The maximum likelihood approach to reconstructingancestral character states of discrete characters on phylogenies. Syst.Biol. 48, 612–622

7 Marshall, C.R. et al. (1994) Dollo’s Law and the death and resurrectionof genes. Proc. Natl. Acad. Sci. U. S. A. 91, 12283–12287

8 Lynch, M. and Conery, J.S. (2000) The evolutionary fate andconsequences of duplicate genes. Science 290, 1151–1155

9 Crandall, K. (2002) Convergent and parallel evolution. In Encyclo-pedia of Evolution (Pagel, M., ed.), pp. 201–205, Oxford UniversityPress

10 Whiting, M.F. et al. (2003) Loss and recovery of wings in stick insects.Nature 421, 264–267

11 Pagel, M. (1999) Inferring the historical patterns of evolution. Nature401, 877–884

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|Letters

The PhyloCode: naming of biodiversity at a crossroads

Ronald Sluys, Koen Martens and Frederick R. Schram

Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, PO Box 94766, 1090 GT Amsterdam, The Netherlands

The rules for the naming of organisms are governed byvarious international Codes of Nomenclature. There areseveral Codes, each covering a different major group oforganisms, such as the International Code of ZoologicalNomenclature (ICZN; metazoa and protozoa), InternationalCodeofBotanicalNomenclature (ICBN;higherplants, fungiand algae), and the International Code of Nomenclature ofBacteria (bacteria and cyanobacteria). These Codes areregularly updated by international commissionsand revisedversions are published only after various drafts havecirculated amongst thespecialists’ community for commentsand suggestions, and following approval of the final versionby an international commission and organization thatrepresents the user community of the Code. For example,the fourth edition of the ICZN was adopted by theInternational Commission on Zoological Nomenclatureafter ratification by the Executive Committee of theInternational Union of Biological Sciences acting on behalfof the Union’s General Assembly [1]. The major goal of allthese Codes is to achieve stability of taxonomic names.

Over the past 15 years, some systematists have claimedthat the current Codes fall short of achieving name stabilityand that their Linnean, basically Aristotelean, typologicalprinciples for defining names for species or groups of speciesare no longer desirable in our modern age, with itsevolutionary, non-typological, biological paradigm. Theyhave also argued that we define names of organisms in acompletely different, non-Linnean way. In this phylogeneticnomenclature, a scientific name for a group of species is to bedefined in relation to its position on a phylogenetic tree. It isargued that a name defined in this way provides importantevolutionary information andismorestable than traditionalnames because the same name will always refer to the samegenealogical group [2–4]. Furthermore, under these prin-ciples of phylogenetic nomenclature, the Latin name of aspeciesshallnolongerbemadeupbyitstraditional twoparts(Linnean, binominal nomenclature) but will consist of onlyone word. A phylogenetic code of nomenclature, thePhyloCode, has been written and is available at http://www.ohio.edu/phylocode/

The pros and cons of both Linnean and phylogeneticnomenclature are currently hotly debated (cf. [3,5–9]), butCorresponding author: Ronald Sluys (sluys@science.uva.nl).

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there is, at present, no consensus as to which system wouldoffer the greatest stability of names. However, the generalconsensus that also emerged is that: (i) theoretical andpractical consequences of phylogenetic nomenclature mustbe explored, (ii) exploratory names and definitions coinedunder the rules of the PhyloCode would not be valid, and(iii) the debate over the differences of approach betweenthe PhyloCode and the traditional Codes might eventuallyimprove biological nomenclature.

However, the future of biological nomenclature mightbe rather different with the announcement [10] of theforthcoming First International Phylogenetic Nomencla-ture Meeting in Paris (6–9 July, 2004). In the circular forthis conference (see http://www.ohio.edu/phylocode/) it isstated that ‘Papers presented at the meeting will beassembled into a symposium volume…whose publicationwill coincide with the implementation of the PhyloCode.This volume will represent the official starting point ofphylogenetic nomenclature as implemented in the Phylo-Code…’ [our italics].

We welcome any effort that explores the extent to whichphylogenetic principles can be implemented more effec-tively into the theory and practice of systematics.Phylogenetic revolutions of the past have invigorated thediscipline of systematic biology. However, we deplore asituation in which two, very different, nomenclatural codeswill compete to govern the rules for naming organisms.Every practicing taxonomist would be faced with thedilemma of having to choose which of the two nomencla-tural codes to use in the definition of names. Furthermore,editors of scientific journals will have to decide whether toaccept taxonomic papers defining names according to thePhyloCode or the traditional Codes. Some journals mightdecide to publish only names coined according to thetraditional, Linnaeus-based codes, whereas others mightaccept only papers applying phylogenetic nomenclature.We feel that this state of affairs will be detrimental to

describing and cataloging the world’s biodiversity and thatconfusion will reign. There are already too few high-quality international journals willing to publish basictaxonomic research, in spite of the fact that the descriptionand conservation of biodiversity is greatly dependent onsuch studies. The unilateral implementation of thePhyloCode might indirectly result in the number ofjournals publishing taxonomic studies being reduced yetagain. We run the risk that agencies and public bodies whorequire, and are increasingly demanding, taxonomicinformation will look upon systematists as an assemblageof petulant quibblers.

References

1 International Commission on Zoological Nomenclature, (1999) Inter-national Code of Zoological Nomenclature, 4th edn, InternationalTrust for Zoological Nomenclature

2 de Queiroz, K. and Gauthier, J. (1994) Toward a phylogenetic system ofbiological nomenclature. Trends Ecol. Evol. 9, 27–31

3 Bryant, H.N. and Cantino, P.D. (2002) A review of criticisms ofphylogenetic nomenclature: is taxonomic freedom the fundamentalissue? Biol. Rev. 77, 39–55

4 Pleijel, F. and Rouse, G.W. (2003) Ceci n’est pas une pipe: names,clades, and phylogenetic nomenclature. J Zool. Syst. Evol. Res. 41,162–174

5 Dominguez, E. and Wheeler, Q.D. (1997) Taxonomic stability isignorance. Cladistics 13, 367–372

6 Nixon, K.C. and Carpenter, J.M. (2000) On the other ‘phylogeneticsystematics’. Cladistics 16, 298–318

7 Benton, M.J. (2000) Stems, nodes, crown clades, and rank-free lists: isLinnaeus dead? Biol. Rev. 75, 633–648

8 Brochu, C.A. and Sumrall, C.D. (2000) Phylogenetic nomenclature andpaleontology. J. Paleontol. 75, 754–757

9 de Queiroz, K. and Cantino, P.D. (2001) Phylogenetic nomenclatureand the PhyloCode. Bull. Zool. Nom. 58, 254–271

10 Donoghue, M.J. and Gauthier, J.A. (2004) Implementing the Phylo-Code. Trends Ecol. Evol. 19, 281–282

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Implementing the PhyloCode

Michael J. Donoghue1 and Jacques A. Gauthier2

1Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520, USA2Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA

The First International Phylogenetic Nomenclature Meet-ing is scheduled to take place in Paris, 6–9 July, 2004. Itsaim is to advance the implementation of the PhyloCode(http://www.phylocode.org), which governs a new systemof nomenclature designed to name the parts of the Tree ofLife by explicit reference to phylogeny [1]. The Parismeeting will bring into existence an International Societyfor Phylogenetic Nomenclature (ISPN), which will governthe use and further development of the PhyloCode andoversee the proposed name registration system. Contrib-uted talks will highlight the application of phylogenetic

naming within many major groups of organisms, therebeing much still to be learned about how best to framephylogenetic definitions to accommodate phylogeneticuncertainty, ensure continuity with the taxonomic litera-ture, and so on. Ultimately, the plan of the Society is toproduce a volume (or perhaps several) that would serve asthe official starting point for the PhyloCode.

The PhyloCode provides an alternative to the rank-based nomenclatural system embodied in the currentbotanical, zoological and bacteriological Codes. Namingunder the traditional Codes is tied to the assignment ofcategorical ranks (family, genus, etc.). Consequently, aclade whose composition and diagnostic characters haveCorresponding author: Michael J. Donoghue (michael.donoghue@yale.edu).

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