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Attacks on Taxonomy

Roger Harris

Most people view taxonomy as a rather dry field of science, so when an online auction to name a new species of Bolivian monkey brought the science of classification to the public's attention, taxonomists were surely delighted. Among the bidders was television celebrity Ellen DeGeneres—who lost to the winning bid of $650,000.

But the publicity did little to unite two camps engaged in a debate that threatens the very foundations of the nomenclatural edifice upon which all of modern taxonomy is built. The melee, reports of which are turning up in popular magazines, is between some scientists who want to implement the PhyloCode, a new method of naming taxonomic groups, and those who want to keep the existing system.

The PhyloCode would name and organize living things based on common ancestry and the branching of the evolutionary family tree. It is based explicitly on phylogeny, the evolutionary history of a species or higher taxonomic group.

Its proponents mean to replace the venerable system developed by Carl von Linné (Carolus Linnaeus, 1707-1778), the father of modern taxonomy, in the mid-1700s and used universally by scientists since then. Linnean classification organizes species in a hierarchical scheme based largely on similarities in their forms and other traits that usually, but not always, reflect evolutionary relationships.

In a hypothetical example of how Linnean naming works...Click to Enlarge Image

Unlike the PhyloCode, Linnean taxonomy does not formally incorporate phylogeny. However, its ranks (species within genus, genus within family, family within class and so on) imply evolutionary relationships. The main drawback of the Linnean system is that groups must be named with suffixes that denote their rank in this hierarchy. For instance, all animal families end in -ae, as in Hominidae. Reclassification of an existing species or discovery of new one can lead to changes in rank and therefore require renaming whole suites of taxonomic groups—a cascade of renaming—even without any new information on those groups. The Phylo-Code solves this problem.

The core proposition of the PhyloCode is to abandon Linnean hierarchical ranks and recognize only species and clades. (A clade is a group of all the organisms that share a particular common ancestor.) The scheme does not dispense with hierarchical organization, as clades will be nested within one another according to phylogeny. The key advantage is that changes made in one part of a classification do not require altering other group names. The PhyloCode's use of common ancestry to establish taxonomic relationships—the  practice called cladistics—has received greater impetus in recent years. Molecular data enable workers to determine relationships with greater certainty than using physical resemblances alone.

Although the clade concept is well defined, PhyloCode workers have not yet established rules for converting existing species names or for naming new species; at least a dozen proposed methods are on the table. Several involve retaining the binomial name (genus, species: Homo sapiens) but formatting it differently to distinguish from clade names, so that human beings might become homosapiens in the Hominid clade.

How would this system affect naming of new species? Robert Wallace, discoverer of the monkey whose naming rights were up for auction, and his team used Linnean rules. If the monkey's name is changed according to PhyloCode rules, it could end up quite different from what the winning bidder, an as-yet-unnamed commercial enterprise, had in mind. Perhaps callicebusmicrosoftii, or callicebuswalmartus?

Supporters say the PhyloCode is simple and will properly reflect evolutionary connections between species, thus promoting stability and clarity in nomenclature. Kevin de Queiroz, a research zoologist at the National Museum of Natural History and an early architect of the PhyloCode, says that, with the phylogenetic system, names of taxonomic groups "will make more sense from an evolutionary perspective."

But the PhyloCode is meeting resistance. Critics say that the Linnean system effectively organizes and conveys information about taxonomic categories at all levels of biological organization and that replacing this system does not justify redefining millions of species and higher taxonomic levels. If the PhyloCode is adopted, the change could mean reworking the names of 1.75 million species (and counting).

According to Michael Benton, chair of vertebrate palaeontology at the University of Bristol, the proposed changes for species names will require systematists to redefine all the species named so far. "This opens up endless vistas of fruitless time-wasting and bickering," Benton says, "and for no benefit whatsoever." He worries that the arguments will result in loss of funding and respect for taxonomy.

De Queiroz argues that much of the protest is overblown. "The system that we‘d like to replace is virtually unknown to the general public," he says. "We're not talking about replacing names; we are talking about replacing the rules governing those names."

Even if academic, the debate has  implications. Implementing the Phylo-Code could profoundly affect global biodiversity catalogs.

One of these is the Catalogue of Life, a coordinated effort to categorize and document all life on Earth. In March, Catalogue of Life scientists announced they now have information for half a million species in their database. The work continues apace. Yet there's barely a nod to the PhyloCode in the relevant literature.

Paul Kirk, a biosystematist at CABI Bioscience, a nonprofit life-sciences research organization collaborating on the project, points to "friction between those who wish to represent life on earth in a 'PhyloCode' way and those who wish to follow the traditional Linnean hierarchy." Although the Catalogue of Life is "firmly based in the Linnean system," the project's participants are talking about how best to manage a possible merger of the systems.

Frank Bisby at the University of Reading, executive director of Species 2000, another Catalogue of Life partner, believes that cataloging efforts can readily incorporate whatever classification system is used by taxonomists. "We're not taking a precise position," he says. "We're asking the specialists to keep us up to date, and that means in one group of organisms we're using natural [Linnean] concepts, while in others we're using the modern [phylogenetic] systems.… There's no claim the database tree is perfect or accurate."

Paul Kirk observed that the two systems "should be able to run in parallel." But Benton is less sympathetic: "In understanding biodiversity, the PhyloCode merely introduces semantic debate; it can provide no enlightenment of real issues."

At the moment, the Linnean camp has the upper hand, with the weight of numbers and of history. But the PhyloCode is gathering support. Will Ellen DeGeneres get to name her monkey after all?—Roger Harris

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