"Character"

[Robin Leech]

Hi Don,

In this case, I was merely trying to assemble a set of features that are
common to all mammals (that everyone recognizes are characters of mammals)
BEFORE launching into a set of the narrower, more specific characters of
select mammals.  Thus, birds would not have the mammary glands and teeth,
and they have feathers rather than body hair (yeah, I know, after you pluck
all the feathers, you singe the corpse to remove hair).

If you will recall, my response was in relation to features that are not
wide-spread in organisms, and my point was that the wide-spread characters
are there, but that at a generic, or even a family, level, we acknowledge
them silently and not directly. We do this by "knowing" Characters 1-5 to be
present for a mammal, then assembling a number of organisms that we put into
taxa within and under these characters.

Unless I am missing something, stating that an organism has hair, or does
not have hair, is stating the presence or absence of a character without any
further assessment.  If the nature of the body hair is important for
distinguishing between species within a taxon (say a family or genus), then
the character state would denote things like quantity, length, texture, etc.

This is the way I have always understood the distinction between character
and character state.

To put this another way, if you are describing and listing the characters of
the Class Aves, I do not think that you would state "Mammae and teeth
absent", and similarly for the Class Mammalia, you would not state "Feathers
absent".  In discussion with students, you would probably comment that birds
do not have mammae and teeth, and that mammals do not have feathers.

If, on the other hand, you were making a key to distinguish birds from
mammals, then you would state the presence or absence of these features.
But, a key is merely a tool for identification, and it should not reflect
either classification or phylogeny.

If a group of organisms has never had a certain character (e.g., the
ancestors of birds lacked mammae), I have trouble assigning a character
state.  If the extinct ancestors of a group of organisms had a certain
character which is absent in extant forms (e.g., apterous hyms, groppers,
flies, beetles), then a character state can be assigned.

In my view, a character state must reflect some sort of change of state of a
character between related organisms, and not the fact that the character has
never been a feature of the organisms or their ancestors.

Robin


----- Original Message -----
From: <Don.Colless at CSIRO.AU>
To: <TAXACOM at USOBI.ORG>
Sent: Wednesday, July 10, 2002 10:44 PM
Subject: "Character"


> Robin Leech wrote:
>
> "I believe that the following "characters", without assessment of
character
> state, work across widely different taxa:
>
> "Character 1" - 4-chambered heart
> "Character 2" - body hair
> "Character 3" - warm blood
> "Character 4" - vertebrae
> "Character 5" - mammary glands
>
> If you add more "characters", (at this point without assessment of
character
> state), the focus is narrowed, as I shall show below"
>
> With respect, this illustrates pretty nicely a usage that distinguishes
> poorly between "character" and "character state" - indeed, it seems to me
to
> confuse them, to the detriment of clarity (see the paper I quoted -
> Sys.Zool. 34:229, 1985). E.g., his Character 2, "body hair" seems to be
used
> in the sense of  "body hair present", which is one state of the character
> (sens. mihi) "body hair present or absent".. Is this nit-picking? I regard
> it as an attempt to get a clear terminology.
>
> Don Colless,
> CSIRO Div of Entomology,
> Canberra.
> email don.colless at csiro.au
> tel. (02)62464270
> tuz le munz est miens envirun :