Last summer on a warm Paris morning, a few dozen members of the International Society for Phylogenetic Nomenclature gathered at the National Museum of Natural History. The occasion was a talk by Jason Anderson, a professor of veterinary medicine at Western University of Health Sciences in Pomona, California. Anderson’s talk—the fifth of the day—was about Lepospondyli, an extinct group of small four-limbed creatures that may be the ancestors of modern amphibians. To the uninitiated, it would have seemed deeply pedantic: The title of the talk was “Phylogenetic Taxonomy of Lepospondyli: Top-Down Versus Bottom-Up Approaches to Nomenclature in Uncertain Topologies.” Yet Anderson’s real subject was a revolution that could shake the foundations of how we describe life on Earth.
The 60 taxonomists from 11 countries who came to Paris for the society’s inaugural meeting had a radical agenda: to overthrow the system of classifying species that has reigned for a quarter of a millennium and replace it with a new one called the PhyloCode. Proponents of the PhyloCode say the old system, originally developed by Swedish botanist Carolus Linnaeus before Darwin discovered natural selection, is so archaic that every taxonomic grouping needs to be redefined. It’s a plan as ambitious as it is controversial. Science is supposed to shed its old habits when better ways of doing things come along. But who decides when one way of doing things is better than another? And what happens when not everyone agrees? “Science the process is objective,” says Yale paleontologist Jacques Gauthier, one of the leaders of the PhyloCode movement. “But scientists are people, and they aren’t objective.”
At the conference l’esprit révolutionnaire was in the air, and it was infectious. A pair of French graduate students were greeting conferencegoers at the door, wearing T-shirts that read “Join the Rebellion!” and “PhyloCode, May the Force Be With Us!” During coffee breaks, scientists chatted about “winning over hearts and minds.” Depending on how you look at it, their efforts are either heroic or quixotic. A century from now, Gauthier says, “People will look at this as history being made—or they’ll have a big laugh at our expense.” Either way, this revolution will not be televised.
Kingdom, phylum, class, order, family, genus, species: Every organism belongs to a species, every species to a genus, and every genus to a family, right on up the chain. When Linnaeus developed this system in the middle of the 18th century, evolution was still an exotic hypothesis, and fossils were thought to be the remains of animals that hadn’t made it onto Noah’s ark. Linnaeus himself freely mixed biology and theology: He believed his classification scheme was a window into the divine order of the universe. “God created, Linnaeus arranged,” he noted.
Since Darwin, however, most scientists have agreed that life on Earth is linked in a giant evolutionary tree, with single-celled organisms at the root and modern species at the tips. Between that root and those tips lie millions of branching points, representing historical moments of evolutionary divergence. The Linnaean system predated this theory by a century, but it worked because its nested hierarchy was much like Darwin’s tree of life. Linnaeus cataloged the natural world by grouping things that looked alike; Darwin showed that things that look alike tend to be closely related. As evolutionary theory evolved, however, the system had to be jury-rigged. In the 1960s, the German entomologist Willi Hennig invented cladistics, a method of determining which branches go where on the tree of life. Since then, taxonomists have tried to group organisms according to common ancestry rather than mere similarity.
The PhyloCoders don’t think that they’ve done a very good job. Regrouping species according to cladistics has only complicated an already confusing and outdated system, they say. Better to start from scratch, with taxonomic groups defined solely by their position on the tree of life rather than by common traits. In Gauthier’s words: “The feathers don’t make the bird; the bird makes the feathers.” Under the traditional system, for example, mammals might be defined as warm-blooded animals with hair and mammary glands (in fact, there’s no single definition, and at least 10 have been used over the years). Under the PhyloCode, they might be defined as all creatures descended from the most recent common ancestor of Homo sapiens and the platypus. The new definition is the equivalent of pointing to the tips of two twigs on the tree of life, tracing the branches back to where they meet, and describing the taxonomic group as everything in between.
What about all those hierarchical ranks in the Linnaean system, like phylum and family? Because they are just artificial constructs that reflect nothing inherent in the natural world, they become unnecessary under the PhyloCode. Homo sapiens would still belong to a taxonomic group called Mammalia, but Mammalia would no longer be a class. Thus every taxonomic grouping would get a new definition and in some cases even a new name. Gauthier says, “Everything else has changed since Darwin, but not this.”
Gauthier grew up in central California, on the leeward side of the Sierras in what he calls cowboy country. He wears string ties and speaks with deep, elongated vowels, gesticulates like a traveling preacher, and has a fondness for phrases like “that’s the way the weenie wiggles.” Gauthier also happens to be one of the most important vertebrate paleontologists of the past 50 years. He was responsible for much of the landmark work that affirmed the theory that birds are living dinosaurs.
Gauthier’s coconspirator in the PhyloCode movement, Kevin de Queiroz, couldn’t be more dissimilar. De Queiroz is a curator of amphibians and reptiles at the Smithsonian’s National Museum of Natural History. He has the earnest, well-groomed look of a retired Air Force pilot, with a runner’s build, cropped hair, and a voice that makes far fewer trips across the tonal register than Gauthier’s. While Gauthier is happy to invent his own folk taxonomies—dividing Homo sapiens into those who treat garlic like a spice and those who treat it like a vegetable, for instance—de Queiroz tends to preface every answer with a pause for deliberation. One colleague calls them “the odd couple.”
They met in graduate school, first at San Diego State University, where they both received master’s degrees, and then in the Ph.D. program at the University of California at Berkeley in the early 1980s. They shared the same adviser there, Richard Estes, and wrote papers together on the phylogeny of lizards. As part of their work, they created a lizard family tree, but when they began to assign names to the important branching points on the tree, they realized there were more groups to name than there were ranks in the traditional system. “I started using these exotic ranks like parvorder, cohort, and microorder, and all that kind of crap,” Gauthier says. “Then we’d learn more about the tree, and all the names would have to change. I thought, ‘That sucks. All these ranks, they’re a problem.’ ”
ORDER IN THE COURT
The traditional Linnaean system for classifying organisms and the upstart PhyloCode look very similar at first glance. Species are organized in a branching hierarchy, and their names bear more than a passing resemblance. But a closer look reveals some fundamental differences. In the Linnaean system, groups of organisms are nested within each other based on their physical similarity. The hierarchy is organized in neat rows so that every species belongs to a family, every family to an order, and so on. The PhyloCode does away with these strict rankings. Instead, it classifies species in a true family tree, with each organism connected to others by common ancestry. Biologists now know, for instance, that crocodiles and birds are descended from the same early reptiles. The PhyloCode reflects this by grouping Crocodilia and Aves on adjacent branches that lead back to the group Reptilia. Taxonomists have tried to reshuffle the Linnaean system in recent years to take common ancestry into account, but vestiges of the old thinking remain. For example, in the Linnaean scheme above (one of several configurations), Reptilia and Aves are both major classes of equal rank in the hierarchy.
Proponents of the PhyloCode have yet to settle on a convention for naming individual species. In the version above, proposed last year by Benoit Dayrat, a postdoctoral fellow at the California Academy of Sciences, species names would keep their original Linnaean epithet but would also include the name of the scientist who first described them and the year in which he or she did so. Humans, for instance, would no longer be Homo sapiens but rather sapiens Linnaeus 1758.
