Tree of life proposal divides scientists

BY GLENNDA CHUI
Mercury News Science Writer

A ROSE is a rose -- but it may not belong to the family Rosaceae forever.

In a highly controversial plan that could shake biology to its core, a few maverick biologists are proposing to abandon the traditional way of naming and ranking every living thing on Earth, a system invented 250 years ago by the Swedish botanist Carolus Linnaeus and a staple of textbooks to this day.

It was a good system for its time, critics say, invaluable for describing how one organism arose from another and how creatures as big as whales, as tiny as germs and as self-important as people are related.

Kingdom, phylum, class, order, family, genus and species -- the traditional hierarchy has been memorized by generations of students with the help of phrases such as King Philip Came Only For Gold and Silver.

But now, critics argue, the system is swamped by the sheer volume of information pouring in from genetic studies, which are rearranging the branches and twigs of the tree of life at a dizzying rate.

They say there are simply not enough ranks in the traditional system to encompass this growth spurt. In place of Linnaeus' creation, they want a family tree without ranks, as free-form and flowing as evolution itself.

``I think it's the greatest thing since sliced bread,'' said Michael Donoghue, director of the Harvard University herbaria and a proponent of the new scheme. ``It's the beginning wave of something that's probably going to happen -- and people aren't going to like it.''

Which appears, at this point, to be an understatement.

``It's moronic!'' said William Burger, curator of botany for the Field Museum in Chicago, expressing the sentiment of a great many of his colleagues at the recent International Botanical Congress in St. Louis.

``When you've got a system that's worked for 200 years,'' he said, ``who the hell cares about the phylogeny of these plants?''

Phylogeny?

It's a fancy word for evolutionary relationships, and it's the heart and soul of biological classification.

When Linnaeus began his ambitious work of classifying everything in the animal, vegetable and mineral kingdoms in the 1700s, Charles Darwin's theory of evolution was still a century away, and each type of living thing was thought to have been separately created.

Linnaeus divided the animal and plant kingdoms into classes, and then again into genera and species, based on the superficial characteristics of organisms -- say, whether the reproductive organs of a flower were out in the open or hidden.

As more species were discovered, scientists were forced to add more categories to the Linnaean hierarchy, and they changed it to reflect what they knew about evolutionary relationships.

So, for instance, in the current version the human lineage goes this way:

Single-celled creatures called eucaryotes gave rise to metazoans, the multicelled animals. Metazoans begat chordates, which have rods of cartilage supporting the nerves that run along their backs. And they in turn spawned animals with backbones, four-legged animals, mammals, primates, hominids, early humans and us.

In the language of classification, we belong to the Eukarya, the Metazoa, the phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Mammalia, order Primates, family Hominidae, genus Homo and species Homo sapiens.

But as the tree of life gets more complicated, researchers continue to discover new and interesting groupings that they want to formally name so they can communicate more easily among themselves.

Convention invention

They invent new categories -- things such as tribes, cohorts and phalanxes, not to mention supertribes, subcohorts and infraphalanxes -- and wedge them in among the traditional ones.

In theory this can expand the system indefinitely. But in practice it becomes awkward and confusing.

The beauty of the new, rankless nomenclature is that ``you don't have to spend time memorizing whether an infracohort is higher than a subcohort,'' said Kathleen Kron, a botanist at Wake Forest University. ``You can concentrate on evolution and biology and the whole reason we got into this in the first place.''

One of the leading proponents of the new system, known as phylogenetic nomenclature, is Brent Mishler, director of the herbaria at the University of California-Berkeley.

He points out that the family tree for the 300,000 species of green plants alone, if printed out on a very wide roll of computer paper, would be nearly one and a half miles long. On that tree are hundreds of thousands of branching points, each one giving rise to a group of plants that scientists might like to name.

But under today's rules, you can't give a group a formal name without assigning it a rank, too.

And the thought of trying to squeeze all those ranks into the Linnaean system makes Mishler shake his head.

``There's just no way,'' he said. ``You get rid of the ranks. If you're an educated biologist, you just need to know how these (groups) nest inside each other'' -- and that information is widely available in databases that contain diagrams of groups branching off from other groups, like the branches and twigs of a tree.

Under the new system, researchers would be free to name any branch of the tree of life without regard to rank.

But they wouldn't rename existing groups -- ``far from it,'' said Kevin de Queiroz, curator of the national collection of reptiles and amphibians at the Smithsonian Institution. ``We're probably using all the same names and giving them different definitions. So we would still be Mammalia. We just wouldn't care if it was a class or a superclass or a giga-superclass.''

Mishler goes further than most in overhauling the new system, arguing that even the category of species should be abolished. Instead, each organism would go by a single name -- sapiens, in our case. If more than one creature bore the same moniker -- as in the many species labeled alba (meaning white), vulgaris (common) or californicus (from California) -- you simply append the name of the next group up the line, like a schoolteacher distinguishing two Jennifers by attaching their last initials.

Others would keep the idea of species, either with their current names or with slight changes, so humans might become Homo/sapiens or Homo-sapiens, reminiscent of the hyphenated names some people take after marriage.

Which is appropriate, because the whole idea makes a lot of people crazy and has some talking in terms of divorce, so deep is the split between advocates of the old system and the proposed new one.

``It looks great when all you see is a theoretical concept on the board,'' said Barbara Ertter, collections manager at the UC-Berkeley herbaria. ``But I rejected it on the grounds that it's going to screw up a system that is working.''

Dick Brummitt, a botanist at the Royal Botanic Gardens in Kew, England, adds that if some researchers want to use the new system, ``it's not for me to stop them. But if they think other people are going to stop using traditional names, they're mistaken. The great majority are totally against what these people are trying to do.''

Opponents fear that a new system would lead to chaos: With two separate types of names floating around, they say, biologists would have difficulty searching through past studies for things that are relevant to their work. Herbaria, those repositories of plant specimens, might have to relabel their collections at great expense.

Given these potential drawbacks, many scientists feel themselves uncomfortably straddling the fence. They can see the logic of the new way of thinking. But they fear that without some sort of ranking it will be much more difficult to communicate, in words, the relationships between the organisms they're studying.

``In practical work, as opposed to theoretical work, one has to come to grips with what has already been done and put it into some kind of framework,'' said Malcolm McKenna of the American Museum of Natural History in New York, who recently co-authored a book classifying all the mammals. ``I find myself trying to accommodate both worlds.''

Mixed emotions

David Maddison, a specialist in the evolution of beetles at the University of Arizona and one of the creators of the Tree of Life Web page, admits, ``I haven't decided personally what I'm gonna do the next time I get around to doing some classifications.''

Proponents of the new nomenclature are now engaged in writing rules, which will be known as the PhyloCode. It will take them a few years yet.

They acknowledge that they may never win over the senior scientists who sit on the committees that determine the rules of nomenclature for various fields of biology. But they are convinced that the next generation of leaders, who grew up with computers and are comfortable with the idea that a diagram can supersede words, will take to the new method and make it their own.

And if the new code does not succeed -- well, that would be nothing less than the survival of the fittest at work.

``We're almost counting on the older generation of people to be resistant. That's the way it works,'' said de Queiroz of the Smithsonian. ``That's not necessarily a bad thing. It keeps crazy ideas from spreading too quickly.''

It's a sort of natural selection, he said. If people find the new system is handier than the old, ``it will succeed and replace the other one. If it doesn't, it won't. That's how we prefer it to be.''