deepreef at BISHOPMUSEUM.ORG
Mon Jan 14 09:33:15 CST 2002
> >I hope that clears up the point I was trying to make, but I fear
> >I've only made things more confusing....
> I'm afraid so...
The dilemma I face is whether to attempt once more to clarify my point, or
simply give it a rest for the benefit of others on this list who remain
uninterested in this thread. Given that the "D" key is an easy strike (I
know because I use it often myself), and fair warning was given in my
previous post, I will try yet again to get this point across.
> Sorry - I can't see any difference between this statement and
> your previous one
But do you still feel that one point was "abandoned" for another?
> There 's the rub again! What use is a definition if the "thing" it points
> to is changing all the time?
No, the "thing" is *not* changing all the time. The specific "thing" to
which the Phylocode name applies is an actual, tangible entity -- the most
recent common ancestor shared by two stated "points" in an evolutionary
tree. The only part that changes is the interpretation of where to place
that "thing" in the context of other, equally explicitly-defined "things".
Contrast that to the "thing" to which a Linnaean name is applied. The only
unambiguous part of a Linnaean name definition is the primary type (...of
the type species, etc.). If the purpose of Linnaean names was to put a name
on every single unique individual organism, then a single-point definition
is all that we would need. But obviously, we want those Linnaean names to
refer to more than just one individual organism -- we want the names to
apply to all the relevant kin of that single primary-type organism as well.
But nothing in the actual definition of the name allows us to permanently
specify the "endpoint". Without an endpoint explicit in the definition, you
cannot permanently anchor the name to a node in a cladogram.
Now, this is not to say that Linnaean names are "bad" -- indeed, as I have
emphasized in previous posts, they have served and continue to serve a VERY
valuable function in biological sciences -- it's just that they are not
ideally suited to represent evolutionary lineages (nodes on a cladogram).
The "thing" that a Linnaean name represents is a human construct -- an
assemblage of convenience for discussing actual living organisms and the
remnants (fossils) of organisms that once lived. In most cases, convenience
of communication is maximized when those names do abstractly represent nodes
in a cladogram -- but as discussed elsewhere, there are exceptions.
My point in all of this (and in the earlier posts to which you have
responded) is that the way in which a Phylocode name is *defined* explicitly
anchors it to a specific node on a cladogram, while Linnaean names are
anchored by definition only to single end-points of a taxonomic tree. As
such, Phylocode names are a more effective and unambiguous (and stable) tool
for communicating how the nodes on a cladogram sit with respect to each
other, than Linnaean names are.
I'm running out of ideas for how to illustrate this point more effectively,
other than resorting to ASCII-art cladograms to show specific examples. I
really don't think I have time for that -- especially considering that my
motivation in supporting Phylocode is *not* related to any anticipation of
using it myself (as said earlier, I doubt I ever will). Rather, my
motivation is to help establish another sandbox in which people who want to
argue about hypothesized relationships among organisms can go play, without
messing up the Linnaean sandbox (in which I intend to continue playing).
There are plenty others out there who understand the Phylocode much better
than I do, so I can only hope some of them will step in to explain the
fundamental distinction (in terms of communicating hypothesized phylogenies)
between single-point name definitions and multi-point name definitions.
> In fact, it is a perfect "thiscar". You know there must be one,
> but at each
> time you look it's a different creature, with different features.
I hope by now you recognize how your "thiscar" analogy doesn't hold here.
In case it's not clear, then maybe it would help if I redefined your
"thiscar" to represent a specific car, with, for example, the license number
"DEF 123". Since you know the license number series is sequential, doesn't
skip any positions, and continues well beyond the "DEF" series, then you
know there is a car out there, somewhere in history, that had this license
number. To carry the analogy further, current cladistic tools allow us to
infer which car that might be, based on various lines of evidence such as
when and where other known licenses existed, and on what sorts of cars. We
all agree that "thiscar" exists, and really is a specific car, but because
the lines of evidence are often so indirect and vague, we get different
people arguing about which car actually is "thiscar". Perhaps, eventually,
our technology will increase to the point where we can actually see the
license numbers on every single car that is out there, and therefore know
with great confidence which car really is "thiscar". (Or, if you maintain
that we can never actually directly observe the evolutionary lineage of
organisms, no matter how good our technology is...then perhaps the analogy
would be better stated as a technology that gives us access to the car
registration records -- which will give is enormous confidence in our
association of licenses to specific cars, if not exactly perfect certainty).
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