Such expressions as that famous one of Linnæus, and which we often meet with in a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent,—the only known cause of the similarity of organic beings,—is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classifications (Darwin, 1859, p. 413f).

Sunday, 28 March 2010

Awareness in Classification 1

Our recent post reveals a few things we believe are simply misunderstandings:
    1) Paraphyletic groups and their reality
    2) Taxa descending from other taxa
    3) Phylocode adjustements to make taxa monophyletic.
Let's change to a more general issue, that of invertebrates. Are invertebrates real? No. Wikipedia begins:
    "An invertebrate is an animal without a backbone. The group includes 95% of all animal species - all animals except those in the Chordate subphylum Vertebrata..."
Can invertebrates be defined? Yes. We could list all taxa that are included within and then list as absent all the characters vertebrates have: "An invertebrate is an animal without a backbone" -- but anything can be so defined. Are invertebrates monophyletic? No. They are paraphyletic, they exclude vertebrates. But if we include vertebrates within them, then do they become monophyletic? Yes, but then that is chordates. Are vertebrates descended from invertebrates? It's a nonsense question as invertebrates do not exist in any meaningful way - from nothing comes something?

Now, replace the terms 'invertebrate' for 'dinosaur' and 'vertebrate' for 'bird'.

To say dinosaurs are amniotes is like saying invertebrates are animals. Both true but neither telling us what dinosaurs actually are (lots of thing are amniotes). Are dinosaurs monophyletic? Are inverterbrates monophyletic?

1 comment:

Michael said...

"Now, replace the terms 'invertebrate' for 'dinosaur' and 'vertebrate' for 'bird'."

Unfortunately, what your vertebrate/invertebrate scheme is analogous to is not bird/dinosaur but bird/non-avian dinosaur or human/non-human ape. Bird/dinosaur is really no more bothersome than titanosaur/dinosaur. These aren't confusing if you keep your contexts straight, and any words are confusing if you don't, because words, at least those that don't exist solely within some one particular jargon, have multiple meanings.

"To say dinosaurs are amniotes is like saying invertebrates are animals. Both true but neither telling us what dinosaurs actually are (lots of thing are amniotes)."

Here you are confusing description and definition. 'Dinosaurs are amniotes' is descriptive of dinosaurs (like 'dinosaurs can be seen with the naked eye') but not definitional. Some descriptions may be sufficiently precise as to be definitions for things like groups of animals, but that's not usually the case. As long as you grasp the context, that one is describing not defining, I don't see a real problem, or at least not one that is beyond what plagues any naturally developing language.