27 February 2010

One Name, One Taxon -- For One Rank Group

How Many Taxa Per Name?


A while back I pondered a seeming contradiction between the way zoological nomenclature is practiced and what the ICZN actually says. To illustrate, let's consider the case of Columbina Illiger 1811 and Columbina Spix 1825. The former is a subtribe, typified by Genus Columba, and the latter is a genus. It's possible for Columbina Illiger 1811 to include Columbina Spix 1825, although, as I understand it, they would generally be considered disjoint taxa, with Columbina Spix 1825 in another subtribe.

In several places, it seems as though the ICZN would not allow one name to refer to different taxa. The Preamble states that one of its objectives is "to ensure that the name of each taxon is unique and distinct", and Art. 52.1 states that, "When two or more taxa are distinguished from each other they must not be denoted by the same name." Logically, it would seem that Columbina Spix 1825 should be considered invalid, and that Columbina Illiger 1811 should have priority.

But this is not how the code is interpreted. There is an understanding that homonymy only occurs within rank groups (family group, genus group, species group). Since Columbina Spix 1825 is a genus-group name and Columbina Illiger 1811 is a family-group name, they can't be homonyms. (Elsewhere, a term has been coined for such apparent homonyms: "hemihomonyms".)

This understanding is implicit. Nowhere does the ICZN explicitly lay it out. The closest it gets is in Article 53, which discusses the particulars of how homonymy works. It discusses homonymy within the family group, homonymy within the genus group, and homonymy within the species group. Nowhere does it discuss homonymy between rank groups. Only by this omission does the code hint at the idea that homonymy only occurs within rank groups.

I've communicated with several taxonomists, including people involved with the ICZN, and they all seem to agree that this is the code's intent and that the wordings in the Preamble and Art. 52.1 are confusing. Hopefully a future version of the code will clarify this.

When a Code Is Not a Namespace


So, with that more or less settled, now I'm back to my original problem. In Names on Nodes, authorities (such as nomenclatural codes) are treated as namespaces, i.e., sets of distinct names. So far as I know, there is no problem in treating the other codes (including the PhyloCode) in this manner, but apparently the ICZN does not work this way. Suppose I refer to the ICZN using a URI based on its ISBN number: urn:isbn:0853010064. What would the qualified name urn:isbn:0853010064::Columbina refer to?

Here are a few ideas I've come up with.

One Code, Three Namespaces


So the ICZN doesn't function as a namespace—but it does function as three namespaces, one for each rank group. I could use each zoological rank group as a namespace. The only problem with this is that there is no standard URI to refer to each group. At least, I don't know of any—if there is one, speak up! (I suppose I could use the draft BICI standard to refer to the particular page in the code where it defines the rank group in question, but that's a bit awkward.)

Orthographic Differences


Note that Columbina Illiger 1811 is in normal font and Columbina Spix 1825 is italicized. I could use this to distinguish the names from each other, e.g., urn:isbn:0853010064::Columbina (the subtribe) vs. urn:isbn:0853010064::_Columbina_ (the genus). For consistency, this would have to be done to species names as well, e.g., urn:isbn:0853010064::_Columbina+passerina_

This isn't the only way to do it, though. The ICZN makes a further distinction, putting family group names in all-capital letters, e.g., COLUMBINA Illiger 1811. (Although it never states this as a rule, and most publications don't follow this convention.) I could follow this convention in the qualified names, e.g., urn:isbn:0853010064::COLUMBINA (the subtribe) vs. urn:isbn:0853010064::Columbina (the genus). No change would be require for qualified species names, e.g., urn:isbn:0853010064::Columbina+passerina.

Augmented Local Names


Another possibility is to consider the rank group to be an essential part of the name itself. This could be reflected in a qualified name by augmenting the name with a prefix, e.g., urn:isbn:0853010064::fam:Columbina (the subtribe) vs. urn:isbn:0853010064::gen:Columbina (the genus). To be consistent, this would have to be applied to species names as well, e.g., urn:isbn:0853010064::sp:Columbina+passerina.

What About Other Names?


The ICZN has few rules to do with names above the level of the family group, and overall it doesn't govern much about them. Thus there are all kinds of examples of homonymous taxa above the rank of family group. For example, Pterodactyloidea Plieninger 1901 is a suborder which includes Pterodactyloidea Meyer 1830, a superfamily. "Decapoda" is the name of an order-group taxon in two different phyla, Arthropoda and Mollusca. Etc., etc.

I had wanted to be able to use qualified names for all zoological names, but I'm having trouble seeing how that will be possible for those ranked above the family group. I'll probably have to use the coining publications themselves as authorities, or a URI (e.g., an LSID) for each name. Rather inconvenient.

Defining Rank-Based Taxa Mathematically

Let U be the set of all individuals.

Let ranks be represented by a contiguous series of natural numbers (). Let 1 represent the lowest (finest) rank and let some natural number n represent the highest (coarsest) rank.

Let T be a sequence of n sets of type individuals (i.e., individuals represented by type specimens). Let each set in the sequence (other than the last set) be a superset of the next set, i.e., T1 ⊇ T2 ⊇ … Tn.

Let d be a metric function measuring some distance between any two individuals: d(x, y) ∈ ℝ0+ (the set of nonnegative real numbers). Note that, because it is a metric, d(x, x) = 0 and d(x, y) = d(y, x).

For each rank level r, let pr be a function mapping each member, t, of Tr to a taxon (set of individuals): pr(t) := {x ∈ U | for all s ∈ Tr, d(x, t) ≤ d(x, s)}. Let Pr be the image of pr. Then Pr is the taxonomy of rank level r.

Note that some individuals may be placed in multiple taxa of the same rank if they are equidistant between type individuals. These individuals may be considered unclassifiable for that rank. Let U′ be the set of all individuals except for those which are unclassifiable for some rank. Similarly, let P′r be Pr but with all unclassifiable individuals removed from each member taxon. P′r is a partition on U′. For any two rank levels q and r, if q < r, then P′q is a refinement of (or equal to) P′r.

25 February 2010

Tricksy Definitions Expressed Mathematically

Just for fun, here are a few definitions of nonstandard type to go along with those in the previous post. As any practitioner of phylogenetic nomenclature knows, most definitions are node-, branch-, or apomorphy-based, but there have been a few that don't fall into these categories.

Here are Wagner's (2004) definitions of Panbiota and Biota:

   Panbiota := (Cladeprc)(Homo sapiens).

   Biota := Crown(Panbiota, "extant as of or after 2004").

This is one of the few cases where it makes more sense to define the crown clade based on the total clade rather than vice versa. (Maybe the only case? Not sure.) Technically, Wagner's wording for the definition of Panbiota might be better translated as (sucminprc)(Homo sapiens), but it works out to the same thing.

And here's Clarke's (2004) definition of Ichthyornis:

   Let M := "apomorphy 2" ∩ "apomorphy 5" ∩ "apomorphy 6" ∩ "apomorphy 7" ∩ "apomorphy 8".
   (These refer to apomorphies in Clarke's Ichthyornis dispar Diagnosis.)

   Ichthyornithes := Clade(YPM 1450 Struthio camelusTinamus majorVultur gryphus).
   ("YPM" refers to the Yale Peabody Museum's Vertebrate Paleontology collection. YPM 1450 is the Ichthyornis dispar holotype specimen.)

   Ichthyornis := Clade((M @ YPM 1450) ∩ Ichthyornithes).

Names on Nodes: MathML Definitions (Version 1.1)

After posting Version 1.0 earlier this week, I had a revelation: the cladogen functions are completely unnecessary, and everything would work a lot nicer if I just tossed them. I also realized that there really was no reason I couldn't include the various relations (precedence, immediate precedence, proper precedence, etc.), just in case anyone wanted to do some seriously non-standard definitions. After some significant revisions, I present Version 1.1.

Some examples of the updated notation, using humans (Homo sapiens), platypuses (Ornithorhynchus anatinus), and Dimetrodon grandis, a stem-mammal:

Union. Homo sapiensOrnithorhynchus anatinus = all humans and all platypuses (polyphyletic taxon, also monothetic)

Exclusive Predecessors. Homo sapiensOrnithorhynchus anatinus = humans and all of their ancestors, except for the ancestors shared with platypuses (lineage)

Synapomorphic Predecessors. "milk glands" @ Homo sapiens = humans and all human ancestors to possess milk glands synapomorphic with those in humans (lineage)

Node-Based Clade. Clade(Homo sapiensOrnithorhynchus anatinus) = Mammalia

Branch-Based Clade (simple). Clade(Homo sapiensOrnithorhynchus anatinus) = "Pan-Theria"

Branch-Based Clade (multiple external specifiers). Clade(Homo sapiensOrnithorhynchus anatinusDimetrodon grandis) = "Pan-Theria"

Branch-Based Clade (multiple internal specifiers). Clade(Homo sapiensOrnithorhynchus anatinusDimetrodon grandis) = (unnamed clade comprised mostly of Therapsida)

Null Branch-Based Definition (multiple internal specifiers). Clade(Homo sapiensDimetrodon grandisOrnithorhynchus anatinus) = ∅

Apomorphy-Based Clade. Clade("milk glands" @ Homo sapiens) = "Apo-Mammalia"

Node-Modified Crown Clade. Crown(Homo sapiensDimetrodon grandis, "extant as of or after 2010") = Mammalia

Branch-Modified Crown Clade. Crown(Homo sapiensOrnithorhynchus anatinus, "extant as of or after 2010") = Theria

Apomorphy-Modified Crown Clade. Crown("milk glands" @ Homo sapiens, "extant as of or after 2010") = Mammalia

Total Clade. Total(Mammalia, "extant as of or after 2010") = Synapsida (or "Pan-Mammalia")

Image showing a node-based clade (Mammalia) under a given phylogenetic hypothesis. Click to enlarge. More here.

21 February 2010

Names on Nodes: MathML Definitions (Version 1.0)

I've just posted version 1.0 of the MathML definition for Names on Nodes. This document provides the foundation for the mathematical entities and operations in Names on Nodes. Previously I had posted an incomplete draft version—this is the first complete version, and also the first version with illustrations. It won't be the last version, but it (or a slightly edited version) will be associated with the first release of Names on Nodes.

This document refines and rectifies concepts laid out in my 2007 paper. It's an important milestone to completing Names on Nodes, a project I've been working on for almost six years.

One of the illustrations, showing how the Clade function works.

15 January 2010

Mangani Individual Chart Update

First things first: want to contribute to Haitian relief? Here's a guide to the appropriate charities.



Second things second: I just posted an update to my diagram showing all known mangani individuals.



Previous version here.

I'm trying a different value scheme to differentiate the vertices and the text. I also revised the earliest species (kadabba, ramidus, and anamensis) based on a rigorous review of the primary literature, and added one early species that had been overlooked (praegens, which may be a nomen dubium but is certainly a mangani or stem-mangani). The later species were revised a bit as well, but not as rigorously.

I really wish there were some place that just listed every known locality with its number of specimens and least possible number of individuals. I've been slowly compiling my own as a Google spreadsheet, but I'd like a better way to catalogue it. Hmmm, perhaps it's time to return to another project of mine.

04 January 2010

The Mangani Holotypes, Entry I: Carl Linnaeus (Uppsala domkyrka)

I, Human

Humans are an egotistic species. Ancient writers considered humans to be created in the image of the gods, destined to rule all other entities. We humans have not one, but two major fields of study devoted to ourselves and named accordingly (anthropology and the humanities). Pick up a book at random and its main topic is likely to be humans (or at least anthropomorphized non-humans).

Yet we are also an outward-looking species. Alone among the life forms of Earth, we regard the skies, the deep, the land. We observe what is, fashion tests to determine how it came to be, and speculate on where things are going. We are self-centered, but our curiosity about things other than ourselves is boundless.

One of the best examples of this apparent paradox lies with systematics, the naming and organizing of life. And no one person illustrates it better than the founder of systematics, Swedish botanist Carl Linnaeus.

Out of Chaos, Order

Carl Linnaeus lived during the 18th century, a time when science, in its modern meaning, was still emerging from what had been called "natural philosophy". The term "biology" had not even been invented yet. Microbes and cells had been discovered, but things like evolution, germ theory, genetics, biochemistry, etc. were a long way off. The study of life was largely a chaotic mess.

Carl Linnaeus as a young adventurer, dressed in Sámi clothing, painted by Martin Hoffman.
Enter the organizer: Linnaeus observed natural entities and saw order, not chaos. He began to arrange animals, plants, and minerals into hierarchical groups, first in his notes, then in pamphlets, and finally as a series of volumes, Systema Naturae. He was not the only naturalist of his time to do this, but he went further than most, and enjoyed more success. Unlike many scholars, his brilliance was recognized in his own time.

Perhaps nobody recognized it more than Linnaeus himself. True to his species, he had a healthy ego. "Deus creavit, Linnaeus disposuit," he was fond of saying: God created, Linnaeus organized. He thought enough of himself to slave over his autobiography almost as much as his systematic work. And he thought enough of his species to give it the name Homo sapiens—"wise human"—and place it in an order called Primates—"primary ones".

But religious leaders of the day took a different view of Primates. To them, the idea that humans could possibly be grouped alongside such lowly creations as lemurs, apes, and monkeys (and bats, originally included in Primates but long since removed) was sacrilege. (Compounding this, "primate" is a religious title as well.) The Roman Catholic Papa Clement XIII banned Linnaeus's books outright in 1758 (although in 1774 Papa Clement XIV actually fired his Professor of Botany for deficient knowledge of Linnaeus's system!) (Soulsby 1993:39). Even Linnaeus's own religious leader, the Lutheran Bishop of Uppsala, considered him impious (Aczel 2007), although this was no bar to Linnaeus being ennobled later on, whereafter he was known as Carl von Linné.

Carl von Linné in 1775, painted by Alexander Roslin
Privately, Linnaeus confessed that he would have liked to go even further in arranging humans with other members of Order Primates. He saw no anatomical reason not to include apes, monkeys, and humans in the same genus (which was a much broader category as he used it than as we use it today), let alone the same order. The only reason he did not name us Simia sapiens was because he feared theological backlash. (Linnaeus 1747)

So here we have a man who saw his species as "wise" and "primary", but recognized that it did not stand apart from other species. Subsequent biological research has upheld our connection to other living things. Ethologists have found that other species use tools, communicate vocally, and even domesticate other life forms. Geneticists have discovered that our DNA is little different from that of a chimpanzee. Paleontologists have found series of extinct species showing that we evolved from ancestors that we share with other animals. Phylogenetically, his inclination was correct—we are one of many kinds of monkey.

Today we struggle to find things that make humans unique. There are still a few—for one thing, no other terrestrial species has attempted to catalogue its fellow life forms. Ironically, this effort, which brings us into the fold with other life forms, also sets us apart.

Naming the Animals

"And Yahweh [of the El Gods] sculpted from the ground every living thing of the field and every flier of the sky-waters. And he brought the Human in to see how he would call them. And whatever the Human called it, that was that living animal's name. And the Human called names to all the beasts, to the fliers of the sky-waters, and to every living thing of the field."
—Anonymous Yahudi, Bereshith 2:19–20a (my translation)

Modern zoological nomenclature, as governed by the International Commission on Zoological Nomenclature according to the International Code of Zoological Nomenclature (ICZN), descends directly from Linnaeus's Systema Naturae. Many of his groupings seem quaint or even laughable today, but, on the other hand, many don't, and a large number of the names he coined are still in use (albeit often for somewhat different groups). The tenth edition of Systema Naturae, published in 1758, is considered one of the founding works of zoological nomenclature (along with Carl Alexander Clerck's lesser-known 1757 work, Aranei Suecici ["Swedish Spiders"]). By the ICZN's rules, these are the earliest works to contain valid zoological names.

The ICZN's way of doing things is a bit different from that of Linnaeus and other early systematists. In some respects this may be regrettable (e.g., the tying of names to ranks has led to much nomenclatural instability—in Linnaeus's time names were free to be ranked however the systematist saw fit, without any spelling change required [de Queiroz 2005]). In other ways, there has been improvement. One notable improvement is the mandating of type specimens.

In Linnaeus's works, names are paired with diagnoses—descriptions of the entities which the name signifies. But diagnoses are an unstable way to define biological groups. They may be too general, bringing unrelated forms into the same group. They may be too specific, excluding forms which should rightly belong. Sometimes they are flat-out wrong. Whatever the case, they are constantly revised in the literature.

What biological nomenclature needed was a way of anchoring definitions. Thus, the ICZN (as well as other nomenclatural codes) uses the concept of a type, one entity which "sets the standard" for the entire group. One specimen (a specimen being some object that has been catalogued within a collection) is selected as the standard-bearer for each species name. There are various types of types in zoological nomenclature, but the most important one is the holotype, the one specimen that anchors the name. Other individuals may be included or excluded as the systematist sees fit, but the one represented by the holotype must remain. (Note that, as practiced, this is different from the Platonic concept of an archetype, in that the holotype need not be a "typical" specimen. That concept is too subjective to be useful in science.)

The Human Holotype

The requirement that zoological names must have a holotype was not grandfathered in, or too many old names would have been invalidated. Instead, provisions were made such that subsequent authors could select a holotype if the original author did not. There are certain restrictions on this, set up to guarantee that the holotype is something that the original author would have included.

When Linnaeus named Homo sapiens, he diagnosed it much more succinctly than usual. "Homo, nosce te ipse," "HOMO nosce Te ipsum," he wrote: "HUMAN know yourself." Nothing further needed, at least at the time.

In 1959, in honor of the tenth edition of Systema Naturae's 200th anniversary, W. T. Stearn wrote a commemorative article that, among other topics, addressed the lack of a holotype specimen for Homo sapiens:
"Since for nomenclatorial purposes the specimen most carefully studied and recorded by the author is to be accepted as the type, clearly Linnaeus himself, who was much addicted to autobiography, must stand as the type of his Homo sapiens!"
Although stated jokingly, this meets the ICZN's requirements for the designation of a type specimen. Linnaeus's remains, interred at the Uppsala Dome-Church, are the standard-bearer for the species Homo sapiens (and, by proxy, Genus Homo, Family Hominidae, etc.). A fitting tribute to his brilliance ... and his ego.

The Mangani Holotypes

Like any good human, I am fascinated by my own species. I spend much of my spare time studying our origins. It's tough going at times, because many people are fascinated by the same topic, and so there is a huge wealth of hypotheses, ranging from crackpot to well-substantiated. On one hand, the wealth of material is great, but, on the other hand, it's hard to sort out the solid ideas from the less solid. In short, it's a chaotic mess.

I am no Linnaeus (and I'm sure he would agree), but I like to organize my thoughts. So this is the first post in a series where I will take a look at what anchors we do have in this sea of confusion. One by one, I intend to look at each holotype specimen within the human-chimpanzee group, which I informally call "mangani", as explained in an earlier post.

I haven't decided on a particular order, but in many ways it seems that the most apt way to begin is with the first species to be named.

Carl Linnaeus (Uppsala domkyrka)

CollectionUppsala domkyrka, Uppsala, Sweden (Sverige), Europe
NameCarl Linnaeus
Other NamesCarolus Linnaeus (Latin)
Carl von Linné (after ennoblement)
Carolus von Linné (Latin, after ennoblement)
L. (standard abbreviation in botanical literature)
Remainsinterred corpse
Geographyborn in Älmhult, Småland, Sweden (Sverige), Europe
died in Uppsala, Sweden (Sverige), Europe
Chronologyborn 1707 CE May 23
died 1778 CE January 10
Sexmale
Age71 years
Height~1.8m? ~1.6–1.7m?
Typified Taxa Names
Species Homo sapiens Linnaeus 1758 [holotype]
Superspecies Homo (sapiens) Linnaeus 1758 [holotype]
Subspecies Homo sapiens sapiens Linnaeus 1758 [holotype]

Homo sapiens typifies:
Genus Homo Linnaeus 1758
Subgenus Homo (Homo) Linnaeus 1758

Homo typifies:
Superfamily Hominoidea Gray 1825
Family Hominidae Gray 1825
Subfamily Homininae Gray 1825
Tribe Hominini Gray 1825
Subtribe Hominina Gray 1825
Taxonomy

Although most of the higher taxa have varying usages, the species Homo sapiens is used fairly stably nowadays to include all living humans and their ancestors for approximately the past 200,000 years. More inclusive usages in the past included forms now generally placed in other species, such as Homo neanderthalensis and Homo heidelbergensis. (Genetic data has supported this for H. neanderthalensis [Krings & al. 1997].) Early specimens are similar to Homo heidelbergensis and Homo rhodesiensis, and are often placed in subspecies other than Homo sapiens sapiens (to be detailed in later entries).

Of the higher taxa, the most stable is Hominoidea, which is generally used for the clade of tailless primates (gibbons and great apes, the latter including humans).

Comments

Many things about the designation of this specimen as the holotype are odd, not the least of which is that the individual represented by the specimen founded biological nomenclature. Apart from that, this specimen is not "typical" of its species in several ways. Notably, although Homo sapiens originated in Africa, this specimen is from a boreal peninsula of Europe, where members of the species exhibit some aberrant local adaptations, notably marked depigmentation. Even so, the individual still bears the distinctive hallmarks of the species: extremely high, vaulted cranium with high capacity, large body size coupled with gracile build, extremely flat face and small brow ridges, etc.

Designation of this specimen as a holotype is problematic in that it is not available for study, on religious and cultural grounds. However, the individual is otherwise well-documented, both in writings and paintings, and was physically normal. Additionally, he has dozens of living descendants, via two of his daughters.


Carl von Linné's gravestone, at Uppsala domkyrka. Photo by Wrote.
Biotechnologist Martin Nervall with a painting of his great great great great great great grandfather, Carl Linnaeus. Photo by Teddy Thörnlund, appearing on Uppsala Universitet's page here.

References

  • Aczel, A. D. (2007). The Jesuit and the Skull: Teilhard de Chardin, Evolution, and the Search for Peking Man. Riverhead Books. isbn:1594489564
  • Clerck, C. A. (1757). Aranei suecici, descriptionibus et figuris oeneis illustrati, ad genera subalterna redacti speciebus ultra LX determinati. Svenska spindlar, uti sina hufvud-slagter indelte samt. Stockholmiae.
  • de Queiroz, K. (2005). Linnaean, rank-based, and phylogenetic nomenclature: restoring primacy to the link between names and taxa. Symb. Bot. Ups. 33(3):127–140. Available online at http://si-pddr.si.edu/dspace/bitstream/10088/4506/1/VZ_2005deQueirozSymBotUps.pdf
  • International Commission on Zoological Nomenclature (ICZN) (1999). International Code of Zoological Nomenclature, 4th Ed.
    London: International Trust for Zoological Nomenclature.
  • Krings, M., A. Stone, R. Schmitz, H. Krainitzki, M. Stoneking & S. Pääbo (1997). Neandertal DNA sequences and the origin of modern humans. Cell 90(1):19-30. doi:10.1016/S0092-8674(00)80310-4
  • Linnaeus, C. (1747). [Letter to J. G. Gmelin]. Available via The Linnaean Correspondence, http://linnaeus.c18.net, letter L0783 (consulted 2009 Jan 31).
  • Linnaeus, C. (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. ed. X, tom. I–II. Holmiae: Impensis L. Salvii.
  • Soulsby, B. H. (1933). A Catalogue of the Works of Linnaeus in the British Museum (2nd Ed.). British Museum. Available online in partim at http://www.nhm.ac.uk/resources-rx/files/xi-zoological-works-23636.pdf
  • Stearn, W. T. (1959). The background of Linnaeus's contributions to the nomenclature and methods of systematic biology. Systematic Zoology 8:4–22.