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Re: Princeton Field Guide
Without wanting to get too drawn into species vs genus etc, one of the key
points I presented at SVP, and that Greg has touched on in his post, is that by
using analysis of stratigraphy and ontogeny (amongst other factors), species
become testable hypotheses. Defining taxa is NOT just opinion: this is the old
paradigm, little changed form the days of Marsh and Cope, where every slight
variation in morphology was defined as a new taxon. Coding "taxa" for cladistic
analyses cannot test the validity of species in the same way ... although we
use this approach to show that juvenile specimens not only tend to plot more
basally than the adult forms, but also that they are often the very reason for
polytomy disasters, erosion of node strength and CI/RI.
Arguing over what defines a species or genus is of little importance, other
in maintaining a stable and robust taxonomy: the essential underpinning for
paleobiological studies. Rather, morphologies ("taxa" if you like) need to be
tracked in time, space and through ontogeny in order to understand their change
and variation, but also (significantly) the origin of that variation. Defining
all variation as 1's and 0's makes morphology black and white, but with a good
fossil record (and the Late Cretaceous of North America is exceptional) you get
so many shades of grey that this approach is becoming less useful.
Things are changing. Analysis of morphological change through ontogeny and
high-res stratigraphy is coming to dinosaur groups where it has previously
received scant attention, and it's making sense of some morphological
peculiarities that have remained unexplained until now.
Oh, I just ordered my copy of the Princeton book, and I got 'dinosaurs of the
air' too. I figured I should get it really, what with some upcoming papers and
----- Original Message ----
From: Raptorial Talon <raptorialtalon@gm
Sent: Wed, 20 October, 2010 9:49:07
Subject: Re: Princeton Field Guide
I have 1) a general statement on the matter, and 2) a direct reply to
one of Greg's arguments.
I mostly agree with Jaime here, although I differ slightly in
interpretation. I think that "species" can be defined so as to make it
a term describing real entities (phylogenetic species concept, i.e.
distinct evolutionary destinies), but I would also say that there are,
practical sense, so many hurdles to actually identifying and measuring
species as distinct entities - and to applying any single species
concept across all of biology, without special pleading for umpteen
different subfields - that the concept of "species" in any
hard-and-fast sense is useless. It is good only as an approximation to
ease communication somewhat.
So while species can be defined in such a way as to be clear that they
are logically real, actually applying the definition in the field or
laboratory is a sisyphean task. We know they're there, but we lack the
tools - or the time - to ascertain them. And if we can't consistently
apply the concept in practice, what use is it to science to bicker
over the philosophical minutiae? What use is it, period? Only
consistency of communication springs to mind as potentially being a
legitimate purpose, but even then we have to agree to be flexible and
make concessions now and again.
I think that's at the crux of what we need to be aware of: for we as
humans to be certain, within reason, that an entity is real, we have
to either a) observe it empirically or b) deduce it logically. If we
can see it, we know it's there; if we can use logic to demonstrate it,
we know it's at least possible because it makes logical sense. If we
cannot either observe and measure it on one hand or demonstrate
validity through reason on the other, then we have no way of saying
the postulated phenomenon actually exists. It could, perhaps, but
science can't justify claims about it. I believe "species" can be
addressed logically, as stated, but not
ves us some basis for saying it is a real
concept. "Genus," however, has never been measured, nor to my
knowledge has it ever been given any definition that can validate its
existence through logic alone. The concept is somewhat useful as a
sort of "handle" by which we can mentally "pick up" various similar
species-ish taxa simultaneously - a sort of shorthand, really - but
that's about it. It lets us conceptually grab bunches of species
together instead of listing the whole lot or constantly laying out the
definition of their clade.
Genera are therefore subjective. If we agree on their content by
convention, then so be it, because we know what we mean by it and it
hypothetically facilitates communication. If we start talking about
inclusion or exclusion of taxa according to phylogeny as elucidated by
traits, we're applying objective reasoning to a subjective construct.
That does not work. Only subjective consensus applies to defining
subjective phenomena. So saying that we should or shouldn't include
taxa in a genus based "only" on traits like frill horns or whatnot is
absurd, because we can subjectively attach as much or as little
significance to any given trait as we collectively agree to do.
Greg's subjective preference that we give less value to such features
is not wrong by any means, it's just not the standard agreed upon by a
larger set of people-interested-in-the-issue. Greg's standard has
therefore been excluded by subjective consensus; he is (in my view)
feeling unfairly excluded from the process, or perhaps looking for
consistency with a still-larger set of workers, and so is trying to
use objective reasoning in an appeal to the subjective reasoning of
peers. This happens every day in human life - all human motives and
perceptions are subjective, yet we use objective reasoning to try to
convince others of how their subjective perceptions may be flawed and
why their subjective motives may be worth changing. Whether one enjoys
a movie is purely subjective, for example, yet I've successfully used
in the past. For us as subjective beings, logic is merely a means to
an end when trying to alter another subjective being's psychological
frame of reference.
That's all fine and normal and I sympathize strongly with the
sentiment (believe me . . .), but when we start trying to use logic on
subjective perceptions *as though they were empirical entities,* we
have crossed out of science and into effectively intractable realms of
philosophy. It's OK to discuss it, but if we're interested more in the
science, we need to keep grounded scientific reasoning. And that means
keeping a clear view of what is and isn't measurable and definable.
Some point-by-point responses to a particular line of reasoning:
"It is not possible to define species either, but species are real."
As far as science is concerned. all real things have a definition.
Whether *we* can find a definition and whether a definition is
*possible* are two distinct questions that we need to be careful not
"It is not possible to define life, but it is real."
"Life" is a loaded word. I would argue that reasonable definitions for
it do exist, as long as we're careful about "unloading" it first to
avoid confusion. (Although if if by "life" you mean subjective
conscious experience, I would agree that defining it objectively is a
monumental philosophical problem - but that's a whole other canister
"There is no way to precisely define battleship versus battlecruiser
(HMS HOOD for example) versus heavy cruiser (Alaska class for
That's because, philosophically, there's no such thing as a
"battleship," "battlecruiser, or "cruiser." Let me clarify. The
designs for those vessels exist; the vessels themselves exist as
physical objects. They are real and they are mathematically definable.
But the categorizations for them are ultimately arbitrary human
labels. Yes, one could say "semi-arbitrary," because tonnage and
certain other factors are measurable as portions of a continuum, which
is what such terms are attempting to
in general, the labels themselves have no fixed meaning, and further,
there are so many continua being lumped together (tonnage, dimensions,
# of guns, etc) that a huge number of variations along one or all
continua are possible. We could define every possible combination
along every last axis if we had the time and inclination to do so, but
it's such a complex question that no one has the wherewithal to
attempt it, and that would still leave us with a radically different
form of classification.
In point of fact, there is no *empirical* dividing line along any
continuum at which one category turns into another, except in our own
minds due our own subjective preferences (because in this case we
*want* categories, so we delineate them at our convenience. We could
choose to lump them all into a single category if we desired to do so,
or we could break them down until we only talk about specific designs,
specific mission profiles, or specific vessels). The physical world
only shows that one ship has X guns and another ship has Y, *not* that
this difference has significance in any absolute sense, and therefore
*not* that this difference demands any *specific* nomenclature for
categorization. The only significance is in our minds, and hence the
terms we apply to individual designs are still arbitrary designations
- except insofar as we wish to communicate useful information (so
while we could call a "battlecruiser" a "flying spaghetti warship" if
we so wished, we prefer to use the term that will convey meaning more
effectively to those who might otherwise be confused).
I could lay out how this applies to the question of genera, but I
think everyone can see the parallels well enough.
"Many terms are approximations, it does not mean that they cannot be
used to describe and distinguish basic, comparable types."
Right. Approximations. General notions. Not things we can be definite
about. So not, for example, things we can definitely say include or
exclude any one taxon.
After all, making definite claims from indefi