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Naming the World
From: The Natural History Museum
| By:
Peter Forey |
EDITOR'S INTRODUCTION |
Modern day taxonomy is based on the work of Carl Linnaeus who invented systems of binomial naming and hierarchical ranking in the eighteenth century. Many biologists today argue that this system is out of date and that, with our greater levels of knowledge of evolutionary processes, it no longer serves as a useful tool. Peter Forey of The Natural History Museum, London, presents a lively and informative critique of the traditional, and proposed updated methods, of naming the world. |
 he Natural History Museum is an institution that goes back to 1753 and holds some 68 million specimens, with a wealth of literature that relates to them. It holds representations of a large percentage of the world's biodiversity, and a great deal of the research of the 300 scientists who work there is targeted to understanding the evolutionary relationships of organisms and applying names to species and higher categories in order to convey that information. In other words, we are in the business of systematics and classification; what Sir Peter Medawar described in 1967 as 'a comparatively humble and unexacting kind of science, research into the parish registers of evolution'. I contest that rather dismissive description. What we do is key to all areas of comparative biology and its need has only intensified over the years with our appreciation of the fragility of the world's biota. |
Why do we need classifications?
- To understand what we are trying to save and what we have lost.
- For effective communication--to refer unambiguously to a species or a group of species.
- To be predictive--to say that a species is a member of a genus or family implies some expectation that certain qualities will be found (e.g. drug potential, edibility, behaviour pattern, suitable experimental organisms).
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In other words, names and classifications are a shorthand for organising our knowledge. It is not just mindless cataloguing; they contain theoretical underpinnings of how the biota came to be the way it is. These are activities very far from humble science and parish registers. |
Linnaeus and the origin of binomial naming
Our classifications and system of naming species today stem from the work of Carl Linnaeus. Most people are familiar with the process of naming species using a binomial, for example the herring's proper name is Clupea harengus. We are used to the fact that species are placed in genera, genera in families, families in orders etc. This hierarchy of groups within groups, which we designate with ranks such as Class, Order, Family etc, is known as the Linnean hierarchy. It has served us well for 250 years. Today we use far more ranks than Linnaeus, simply because we know far more organisms than he did. In the image below, the ranks in black are those that Linnaeus used. Those in green are some of the many added later. The species rank, which Linnaeus did use, is in red because this is the 'dynamite' rank as I'll explain later on. There are various international codes of nomenclature set up to regulate the naming of organisms. |
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| The taxonomy of Clupea harengus pallasi, the Pacific herring. | |
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| Carolus Linnaeus (1707-78). | |
But Linnean classification is now being challenged. Many biologists claim that the Linnean hierarchy no longer meets the needs of a modern biologist. Some speak of the poverty of the Linnean Hierarchy; some say that it obfuscates the knowledge we now have about the world; some claim that the theory of evolution cannot be grafted onto the Linnean system of classification, which was devised in a pre-evolutionary world, whilst others claim that biological taxonomy must eventually outgrow the Linnean system. |
In this feature I will introduce a few of the arguments. I do not claim originality for the ideas, equally I do not wish to take blame for the mayhem that new recommendations may cause. I do believe that the anti-Linnean commentators have a point. But, equally I believe that the system which they want to replace it with is short-sighted and could lead to so much confusion that the stated aims of being able to communicate our ideas with clarity and stability will be lost. |
Before I launch into these arguments I will explain what Linnaeus did for us because it is his system that we have inherited, albeit with drastic modification. Prior to Linnaeus' work in the eighteenth century the names of animals and plants were not fixed. Often the actual name that was given was effectively a short description, encapsulating the observable features of the organism. The problem was that different people described it differently. For example the name of a species of the Convolvulus genus was given as Convolvulus folio Althae by Clusius in 1576. In 1623 Bauhin named it Convolvulus argenteus Althae folio. And Linnaeus named it Convolvulus foliis ovatis divisis basi truncatus: laciniis intermedius duplo longiorubus in 1738. |
There was no theoretical underpinning as to why a certain name was given. True, there were people before Linnaeus who recognised the need for conformity and also some desire to try to express the similarities and differences between organisms through classification. But it was done in a theoretical vacuum. Linnaeus, on the other hand, had a clear idea of why the world appeared to be ordered, at least at what he called the genus and species level. For Linnaeus the genus displays the essence--that is, the God-given property which causes its existence. He adopted the Aristotelian logic of sub-division whereby an organism or group of organisms, the genus, has a recognisable essence. And within this there are differentiae--variations on the essence of the genus. The word genus here is used in a philosophical sense but we have co-opted it for use as one of many ranks in the Linnean system. |
Linnaeus recognised that the essence of a plant allows the plant to breed true. Thus the genus was the crucial entity. He believed that the essence of the genus lay in the fructification (the flowers and fruits). So, it was the variation in the parts of the flower and fruit which allowed us to discover the essence. |
There is a very important point to be made here. The descriptions of the essences showed that they were equivalent to one another in terms of the parts of the fructification. So there was, for Linnaeus, the notion that one genus of plants was equivalent to another. The species of genera are the differentia--variations on the generic essence. |
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| Two species of plantain as described by Linnaeus. | |
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The image above shows two species of plantain. Linnaeus named the one on the left 'plantain with pubescent ovate-lanceolate leaves, a cylindric spike and a terete scape' and distinguished it from the one on the right, 'plantain with lanceolate leaves, an almost ovate naked spike and angled scape'. These were the distinguishing features of the species within the genus Plantago which had already been described by its essence. But we could not have a species name without the genus name. You could not call something "lanceolate leaves, an almost ovate naked spike and angled scape". The diagnostic attributes had to be linked with a genus name. Therefore there were always two parts to a species name--the essence (genus) and the differentiae (the species). And like the genus, one species was regarded as equivalent to another. |
Apart from this theoretical justification for genus and species, Linnaeus was above all a practical person. He wanted biologists to be able to remember the names and to memorise the position of one species relative to another. So he did two things. He realised that it would be impossible for people to remember all the long descriptions of genera as names and so he shortened them to one. Linnaeus recognised about 300 plant genera and, as he thought this was the limit of God's creation, he considered that this number was well within the capabilities to anyone to remember. But there were about 8000 species accepted then and he acknowledged that no one could remember all these. In fact, people had started calling the species by number (e.g., Plantago number 1, 2 etc). So, as with the genera, he suggested that we use just a single species name such as Plantago media or Plantago lanceolata. |
And so, binomial naming was invented both for logical reasons--the essence and the differentia--and for practical purposes, that is to memorise a name and it's systematic position. Linnaeus also encouraged the choice of a species name that would most obviously distinguish it in one word from other species. We still try to do this but succeed in only a small percentage of species names. |
There is another important point in Linnaeus' naming. Remember that the name originally was a description of what the species looked like. Having shortened the name to two words it was impossible to encapsulate this description. So, the idea of a type specimen was introduced (although not until some time after Linnaeus). That is an actual specimen on which the species was first recognised. Any future worker who considers that they may have discovered a new species should consult the type specimen of the various species already described to establish whether their new organism is in fact a new species. The Linnean system is often called a typological system. Every organism except one has a type specimen. And this is why The Natural History Museum and others like it are so important because they hold the type specimens. Due to the age and size of The Natural History Museum, many type specimens used by taxonomists to erect names are here. |
There is one exception, Homo sapiens, for which no type specimen exists. William Stearn, a Linnean scholar, suggests in his insightful essay on Linnean classification that as the name Homo sapiens was erected by Linnaeus, and as Linnaeus studied Linnaeus intensively (he wrote his autobiography five times), then it follows that the type specimen should be the skeleton lying beneath a stone slab in Uppsala Cathedral inscribed 'ossa Caroli Linnaeus'. |
Although Linnaeus was certain that his genera and species were natural, he was less certain about the naturalness of the ranks above the level of genus. He used two other ranks, classes and orders, which we still use today. But he admitted that his system of recognising orders and classes was artificial because he differentiated his orders and classes on single characters, not combinations of characters, like the parts of the fructification. |
He also decided that some features were less important for the life of plants than others and, therefore, of limited use. For example, he decided that the petals, sepals and nectaries were of less consequence for a plant's existence than the stamens or pistils, explaining this in a most delightful way: |
The flowers' leaves themselves (:petala) contribute nothing to the generation, but only do service as bridal beds which the great Creator has so gloriously arranged, adorned with such noble bed curtains, and perfumed with so many soft scents that the bridegroom with his bride might there celebrate their nuptials with so much the greater solemnity
So, to summarise, Linnaeus believed that genera and species were real natural entities. He used the binomial species name as a shorthand for the description. The generic name embodied the essence and was necessary both to limit the comparisons which had to be made, and to act as an aide mémoire. He believed that one genus was equivalent to another and he based his genera on a type species, and his species later came to be based on type specimens. |
Taxonomy today
The Linnean taxonomy that we use today is very different in the theoretical underpinning from that put forward by Linnaeus himself. We accept that the theory of evolution is the reason for biological diversity, not special creation. It is genealogical connectedness which is the primary cause of biological diversity and morphological (or genetic) similarity which is the manifestation. We no longer believe that genera and species have essences that can be discovered and described. We no longer accept that one genus is in any way equivalent to another, or that a family of beetles is equivalent to a family of fishes. |
Linnaeus made a logical break between the genus, which he thought was natural, and orders and classes and which he admitted were artificial. If we nowadays make a break at all, and not everyone does, we make the break between the species and the rest. Most people regard the species as the unit of evolution and therefore different from genera etc. |
For Linnaeus, the species, like the genus etc., was a fixed entity. For us, species and species lineages are regarded as mutable and hence are constantly changing. We also, and most importantly, regard it as desirable that our ideas of how species, genera, orders, etc. are related to each other should be reflected in classifications. These ideas change constantly. Our problem is how to hit a moving evolutionary target (the species), and our changing ideas of relationships between organisms (our theories), with a naming system that was originally designed for static, immutable organisms. |
So, there are fundamental differences between the causal phenomena we are trying to explain and encapsulate in our naming and classifications. Yet, with some exceptions we still use Linnean taxonomy. We still use the binomial name. We still use the ranks species, genus, order, class as if they mean something. We still use a typification system up to at least the family level (this is demanded by the Zoological and Botanical International codes). |
The aims of a modern classification and naming system are:
- Information storage/retrieval system (an aide mimoire).
- It should allow (valid) generalisations to be made (Ernst Mayr, the evolutionary biologist, adds the word 'valid' by which he means evolutionary).
- It should be predictive: we should be able to infer properties that were not part of its construction.
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At the same time we would like a taxonomic name to be:
- Unambiguous: the meaning of the name should be clear and mean the same thing to everyone.
- Unique: there should be one name for one entity.
- Stable: the name once established should refer to the same thing, and the same thing should not change its name.
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Sadly, such desirability is very far from being achieved. For now I just want to concentrate on the third of these items in the wish list. This is the one that causes the most difficulty and is the source of most irritation amongst non-taxonomists. One of the most frequent complaints I get is "Why do you keep changing the names?" To which I reply, "We do it to reflect our changing ideas of relationship." In other words, to keep you, the user, up to date. |
There are several reasons why a change in our ideas about relationships can cause a change in the name. The most frequent reason occurs at the species level, when a species is moved to another genus because it is now thought more closely related to a different set of species in a different genus. |
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| The changing name of the tomato. | |
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One very dramatic example, with potentially expensive consequences, concerns the humble tomato. The tomato has had a long and confused history of naming. In the days before Linnaeus it had many descriptive names including Poma amoris (the apple of love). However, Linnaeus called it Solanum lycopersicum: it was placed in the same genus as the potato (Solanum tuberosum). However, sometime after Linnaeus, someone decided that the tomato really belonged in the genus Lycopersicon. So, the name should have been Lycopersicon lycopersicum. But botanists do not allow tautologous names (unlike zoologists, who euphoniously named the wren Troglodytes troglodytes). So the specific name was changed to esculentum, giving us Lycopersicon esculentum. |
Sandy Knapp, a scientist at The Natural History Museum, and her co-workers have now shown that the tomato, Lycopersicon esculentum, is really most closely genetically related to some species within the genus Solanum. So to reflect this the species esculentum is moved to become associated with species within the genus Solanum. The genus Lycopersicon is now no longer recognised. So the tomato must now be known as Solanum esculentum. But, esculentum was not the original specific name--it was only changed because of botanical dislike of tautonyms. So it was moved back to the name that Linnaeus originally gave it, Solanum lycopersicum. What goes around comes around. |
This kind of event, whereby species' names change, happens many, many times every year. It causes problems because of the binomial name. Because there are two names to a species, changing ideas of relationship mean that the generic name must be changed. And, in this case, matters are double trouble because of the date priority of the original species name. So, after many years of the tomato being known as Lycopersicon esculentum, it should now be known as Solanum lycopersicum. This could be expensive because it implies that all tomato seed packets need to be reprinted with the genealogically correct species name! |
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| Problems for Linnean nomenclature under phylogenetic revision. | |
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This sort of thing can happen at higher hierarchical levels and it usually has more severe consequences for name changes. The example above is often used by opponents of Linnean taxonomy: Imagine we had a phylogeny of Families of Agamid and Chamaeleonid lizards. Subsequent phylogenetic revisions suggested that some members of the family Agamidae were more closely related to Chamaeleonidae. If we wish to express this new phylogenetic hypothesis, changes in the Linnean classification would be needed. We would have several choices such as upgrading the family Chamaeleonidae to an Order and recognising three families. Or we could recognise just one family (here it would be the family Chamaeleonidae because it was the older used name), and then recognise three subfamilies; Leiolepidinae, Agaminae and Chamaeleoninae. So we've changed the spelling of the words to accord with Linnean rank and, furthermore, the original Agamidae does not have the same content as the new Agamidae. Thus, we change names to reflect changing ideas of genealogical relationships. |
But there is a catch because biologists cannot agree on what type of evolutionary similarity to recognise. |
During the last 30 years there have been considerable, sometimes vituperative, debates over the systematic methods used to discover genealogical relationships. Two particular methods met head-on in the 1970s and 80s. One is the traditional method championed by, amongst others, Ernst Mayr. The other is a method put forward by the German entomologist Willi Hennig. They differ in the kinds of evolutionary similarity they recognise. I will not get into the intricacies of each, but I will point out that the classifications, derived from the results of certain methodologies, imply different things. |
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| Hennig and Mayrian relationships. | |
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In the left hand side of diagram on the above, according to the Hennigian method, species B and C are more closely related to each other than either is to A because they share a unique common ancestor (X) not shared by A. This relationship can be identified because B and C share at least one observable special similarity inherited from their common ancestor and not shared with A or any other species. This special similarity, character 'b' in this diagram, is called a shared derived character or synapomorphy in systematic jargon. B and C are called sister-groups because they share a unique common ancestor (X). B and C are genealogically more closely related to one another than either is to A. This group is called a clade, or a single lineage. The sister-group to a group B+C is species A. Since this systematic method is only interested in recognising these groups or clades it is called cladistics. A Linnean classification expressing this relationship could be written as B and C being placed in one genus and A in another collateral genus. In which case the genus A would be monospecific--it contains only one species. |
The right side of the diagram shows another way of looking at the same genealogy. Here, some overall measure of morphological (or molecular divergence) is indicated by the different lengths of the lines. Character 'b' places B and C as sister groups as in the first diagram. B and C still share a unique common ancestor. However, species C shows eight unique characters, labelled c-k, sometimes known as autapomorphies that serve as fingerprints. Evolutionary taxonomy, as championed by Mayr and Simpson, claims that this morphological divergence is an equally important evolutionary phenomenon. After all, evolution is descent with modification. For example, the presence of characters c-k may have allowed species C to invade a new adaptive zone. Evolutionary taxonomists might well group A and B together because, in character terms, these species have not departed as much from the common ancestor to all three species as has species C. The Linnean classification would place species A and B in one genus and species C in a collateral monospecific genus. |
These two ways of classifying groups, whether they be species or higher ranking taxa, reflect different types of groups. In cladistic classification, the only groups recognised are like B+C, and they are called monophyletic groups. They are defined as having a common ancestor and all the descendents of that ancestor. They are recognised by shared derived characters. However the group A+B, recognised by Mayr is a paraphyletic group. This group contains the common ancestor of A, B and C but excludes one of the descendents, that is C. |
Evolutionary taxonomy recognises that both genealogy and morphological divergence or modification are important. After all, evolution is descent with modification. But exactly when to emphasise one or the other--genealogy or divergence--in a formal system of classification is left to the 'skill of the competent systematist'. In most of our Linnean classifications, different parts of the phylogenetic tree will be classified in different ways. There will be a mixture of mono- and paraphyletic groups. |
The difference between cladistic and evolutionary schools has implications for Linnean rank. In the Hennigian classification, the sister groups we recognise take equal rank. So, it is very clear that just given the Linnean classification that we could reconstruct the genealogical tree. For the Mayrian classification the Linnean rank may mean some measure of morphological divergence--how much we are not told. Effectively, A+B is there to emphasise the distinctiveness of Genus/species C. That is why you see relatively frequent announcements that a newly discovered animal or plant is so unusual, i.e., morphologically divergent, that it must be accorded a new Family, or Order, or even Phylum. So, in this sense, we seem to have inherited and even expanded the idea that ranks--genus, family, phylum--have some kind of essence, some measure of morphological diversity. Linnaeus did believe in genus essences, but not for higher ranks. |
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| The problem of birds and reptiles in the Linnean system. | |
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Lest these arguments seem a bit abstruse, I will give some classic examples of confusion. Perhaps the most obvious candidates in the animal kingdom are the reptiles. Everyone agrees that the diagram above depicts the genealogy where birds are most closely related to crocodiles. However, our standard Linnean classification places birds in one Linnean class, Class Aves, and allies crocodiles lizards, snakes and turtles in another, Class Reptilia. These two ranks at the class level in Linnean classification are not comparable. The Class Aves is a clade--a monophyletic group. Class Reptilia is not, it is a paraphyletic group because it excludes one of its genealogical members--birds. |
There are many examples of this but some of the more familiar are Class Bryophyta (mosses and liverworts), Class Algae, Class Pisces (fishes) and even Class Dinosauria. Just by reading a Linnean classification you would not know that these are not genealogically comparable to Class Angiospermae or Class Mammalia. |
Taxonomy of the future
It is against this background of ambiguity and instability that some people have decided that it is time for change. Two years ago a system of nomenclature appeared on the Web. It is known as the PhyloCode. It arises from the work of two herpetologists, Kevin de Queiroz and Jaques Gauthier, and a botanist, Philip Cantino, although many others have been involved. At present it is only in draft form, for reasons I will explain later. This code for naming stems from the desire to reflect our ideas of genealogy, to avoid the unnecessary name changes when our ideas change, and to get away from the idea that ranks are somehow equivalent to one another. I've already explained that a big part of the problem is Linnean rank. So one of the aims of the PhyloCode is to abolish the rank under PhyloCode nomenclature. There is no family, order, class, etc. Instead there are just names. Furthermore, the idea is to name only clades, that is monophyletic groups. So, there will be vast spreads of the tree of life where we are uncertain whether the species form true monophyletic groups, which will be left un-named, or be named in the old Linnean Nomenclature. |
But the soup gets a little thicker here because monophyletic groups or clades can be defined in one of three ways. |
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| The phylogeny leading to modern birds. | |
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Consider the diagram above which shows a phylogeny leading to modern birds, traditionally called Aves. Let's drop the rank class. This lineage may be considered as a series of speciation events, each split being marked as a node that was occupied by an ancestor 'A'. The intervening sections of the evolutionary history can be thought of as a series of stems. During the evolutionary history of the lineage, changes between successive nodes may be characterised by the appearance of new characters (apomorphies) such as, in this case, feathers, which have been inferred to appear between two nodes. This entire lineage will have a sister group, in this case designated as crocodiles. |
Under what is called a node-based definition (see Figure 1) the name 'Aves' is the name given to a clade stemming from the most recent common ancestor of Struthio camelus (the ostrich) and Corvus corax (the raven). Struthio camelus and Corvus corax are called specifiers. They serve analagous functions as Linnaean types except they have no characters. |
In the stem-based definition (see Figure 2), Aves is named as the clade consisting of Struthio camelus and all organisms sharing a more recent common ancestor with Struthio camelus than with Crocodylus nilotica. So again we have a reference to specifiers but this time one (Struthio camelus) is included and one (Crocodylus nilotica) is specifically excluded. The stem-based definition states that a taxon is more closely related to one specifier than another. |
In the apomorphy-based definition (see Figure 3), the definition is a clade stemming from the first species to possess character feathers, synapomorphic or homologous with that in Struthio camelus. Again there are two specifiers but one is conceptually quite different from the other. |
So what is the problem? It is that we have to know under what definition the name was established before we can refer an organism to the group Aves. During the last few years there have been some spectacular finds of bird-like fossils in rocks from China of about 140 million old. These look like animals traditionally called dinosaurs. Palaeontologists are mostly agreed on the genealogy of these animals. With traditional dinosaurs like Tyrannosaurus they form a series of species that successively acquired bird-like characters. One form, Sinosauropteryx, is covered with tiny filaments, which appear to be the rudiments of feathers. Another, Sinornithosaurus, is covered with structures that have a filament which branches while another, Archaeopteryx, shows structures just like modern day feathers. The snag is what do we call them? Well, that depends on how the definition of Aves was set up. |
If Aves were node-based none of these animals would be included because all occurred in the phylogeny before the common ancestor of Struthio and Corvus existed. |
If Aves were stem-based all would be included, including Tryrannosaurus, because all are genealogically more closely related to Struthio than they are to Crocodylus. |
If Aves were apomorphy-based, Archaeopteryx would be included and Tyrannosaurus would be excluded but we would be undecided about the other two because it all depends on what you accept as being a feather. |
So with this newly-discovered bird-like dinosaur, you would have to know exactly how the PhyloCode name Aves was set up before you could include or exclude your fossil from Aves. You would, in other words, have to go back to the original author of Aves to make your decision. Some similar kind of knowledge is also needed when using the Linnean names, so we have neither gained nor lost anything here. The problem is that if PhyloCode is adopted, we would have to trail through two complete sets of definitions to find the answer. So, in a sense, PhyloCode is adding complexity, confounding the clarity that was asked for in the first place. |
The species question
Lastly, let me turn to species. If there is one word in the biological dictionary guaranteed to start a barroom brawl it is 'species'. Of course, for Linnaeus, the species was nothing special--it was just a variation on the genus essence. But now species are regarded as the engine of evolution. I do not want to get into interminable arguments over the ways we recognise species, I only want to address how we name them. Even here there is more than enough to talk about. |
The reason that PhyloCode remains in draft form is that the proposers cannot agree on how to deal with naming species. At the beginning I outlined how Linnaeus arrived at the binomial two-part name for the species. I also detailed how a species name would have to change should our ideas of genealogy change. This is because the Linnean binomial tells us something about relationships. It tells us that species Lycopersicum is in the genus Solanum and therefore is probably more closely related to the species tuberosum, the potato, which is also in the genus Solanum, than it is to species in the genus Rannunculus. But there is a reverse side to this. Sometimes an investigator may be uncertain as to what genus a species belongs. However, he or she is forced to place it in a genus, or create a new genus, only because of the demands of the Linnean system. |
Therefore, supporters of the PhyloCode want two objectives relative to species names. They want to be able to indicate the phylogenetic relationships of species--that is the whole basis of Phylogenetic Nomenclature--and they want the names to be stable should our ideas change. To me, these are incompatible aims but I will outline some suggestions that have been made. There have in fact been about 15 different suggestions as to how to change the current naming of species. |
Stability is the easiest to deal with. There are currently about 1.5 million species names in use so any suggestions will have to deal with converting those names to some new system like Phylogenetic Nomenclature. |
Of the methods proposed some effectively suggest the maintenance of the old Linnean binomial but proposed to freeze it in time such that any suggested move to reflect a new phylogenetic idea is not reflected in the name. So, going back to tomatoes, if the traditional name of Lycopersicon esculentum became associated with Solanum through phylogenetic revision, then the name would remain as Lycopersicon esculentum. The name could be distinguished from a Linnean binomial in a number of ways, two of which are to spell out the name in entirely lower case or use a hyphen, dash or period, to run the words together into an effective uninomial name. So we could have Lycopersicon-esculentum, not associated with the Linnean genus Lycopersicum. Whether such subtleties will be used and understood by non-taxonomists is a moot point. |
Another set of possibilities which has been entertained is based entirely on the specific epithet of the Linnean binomial. That is Lycopersicon esculentum would simply become known as esculentum. If there were another esculentum we would add a numerical suffix calling it esculentum2. |
Finally, there are people who want the phylogenetic information to be directly linked with the name. To some extent we already do this in the Linnean binomial. The species esculentum is related to other species in the genus Lycopersicon or Solanum, depending on which phylogenetic hypothesis you believe. This is referred to as a taxonomic address. However, it is rather limited. |
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| Linnean names and their alternatives. | |
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Brent Mishler, a botanist working at Berkeley, goes further by suggesting that species are no different from any other Linnean rank. Whereas most people would consider all species as being equal in some sense (for example all species are units of reproductive cohesiveness), Mishler claims they are no different from what would be called genera, families, etc. He therefore advocates the use of the PhyloCode and does away with all ranks, including the rank of species. At the same time he wants to keep phylogenetic information, so he suggests we use a uninomial species name but incorporate the taxonomic address within the name. So, esculentum would be associated with solanum solanacaea solanales eudicota angiospermae tracheophyta plantae life. |
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| 'Sapiens Homo Homonidae Primata Vertebrata Metazoa Eucaryota Life'. | |
The individual words that go to make up the name would be PhyloCode names, subject to the definitions given by the people who erected them. In theory, parts of the name would have to be changed should our ideas of phylogeny change. But remember that the idea of PhyloCode is to erect names that would be stable. So as we currently understand the tree of life we would be known as 'Sapiens Homo Homonidae Primata Vertebrata Metazoa Eucaryota Life'. |
In a sense we have returned to pre-Linnean systems of polynomials--multiple words for naming a species. What goes around comes around! However, this time we are not describing physical attributes by which we can identify an organism. Instead we are replacing it with something conceptual, our notion of the genealogy. |
Whether these ideas for naming species and more inclusive groups will catch on remains to be seen. Certainly there are classifications that use naming systems concordant with those put forward by the PhyloCode. But, at present, they only relate to groups--clades--that are above the species level. They are unfamiliar to us and we have to check whether the names are node-, stem- or apomorphy-based. Of course unfamiliarity alone is no reason to simply reject such schemes. |
But the abolition of Linnean rank, while philosophically sound, may generate unwanted shock waves for biologists who use classifications produced by taxonomists. For example, in biodiversity estimates, it is common practice to simply note the existence of a representative of a family because the organism may be new and can only be recognised initially to family level. Equally, in studies on the patterns of diversity through time, genera and families are used as surrogates for species ranges because of the incompleteness of the fossil record. Such counts and such studies will be impossible under PhyloCode nomenclature and we may indeed have to rely on our creaking Linnean system here. |
I'm not sure where all this will end, although I fear confusion. There have been, and still are, many debates at scientific meetings, on the Web and in scientific journals. All I can tell you is that there are determined attempts to rewrite the Parish Registers. |
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