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).

Tuesday 6 April 2010

Awareness in Classification 2

In response to Michael from last 'Awareness in Classification' post

Several relationships are proposed, some conflict with others:
    1. Bird - dinosaur
    2. Humans - Apes
or:
    3. Bird - non-avian dinosaur
    4. Human - non-human ape
In examples 1 and 2 above dinosaur implies some distinct group of animals, as does apes. In examples 3 and 4 above 'non-avian' stands for 'not-bird', and 'non-human' stand for 'not human'. Thus,
    5. Bird - not bird
    6. Human - not human
It is tempting to explore the idea of what a 'not bird' might be (resisting exploring what a 'not-human' might be): a flower, a rabbit, a house...

Another relationship might be:
    7. Vertebrate-invertebrate
or
    8. Vertebrate-not vertebrate
It is tempting to explore the idea of what a 'not vertebrate' might be: a flower, a rabbit, a house...

One might argue that context is all important. Of course, a 'not vertebrate' doesn't mean a flower. Well, once again, what does it mean? 'Not vertebrates' are paraphyletic. One might re-classify all 'not vertebrates' as vertebrates, thus making 'not vertebrates' monophyletic (One might re-classify birds as dinosaurs making them monophyletic). Does this mean, now, that birds are invertebrates? Prokaryotes are paraphyletic. One might re-classify all 'prokaryotes' as eukaryotes, thus making 'prokaryotes' monophyletic. Does this mean, now, that birds are prokaryotes?

Words do indeed have multiple meanings. A taxon name is best associated with a relationship. Then the meaning can be empirically explored.