[Taxacom] The Reality (or not) of Species (again!)`

Richard Pyle deepreef at bishopmuseum.org
Sun Sep 14 18:11:00 CDT 2008


> I didn't say it wasn't a representation, I said it wasn't 
> reality. 

Fair enough -- my bad on the original wording.

> As a representation of evolutionary history (in 
> contrast to it also being a representation of smoke), I find 
> it un-useful, since it generates no hypotheses.

Yes, but I think that the *point* some of us are making is that the premise
of the so-called "hypotheses" generated by cladograms may be fundamentally
flawed.

> With respect to your essay about species, I think our 
> differences *are* semantic, but no less important for the way 
> they shape our views of evolution.

I would agree with this assertion.

> Consider the cells in a metazoan or land plant. With some 
> exceptions (cardiac muscle comes to mind), most of us have a 
> clear conception of cells as "real" objects. There's an 
> entire field, cell biology, that assumes they are.

When discussing atoms, we think in terms of "reality" at the resolution of
subatomic particles, without getting bogged down in higher resolutions of
physics.

When discussing molecules, we think in terms of "reality" at the resolution
of atoms, without getting bogged down in subatomic particles.

When discussing cells, we think in terms of "reality" at the resolution of
molecules, without getting bogged down in atoms.

When discussing tissues, we think in terms of "reality" at the resolution of
cells, without getting bogged down in molecules.

When discussing individual organisms, we think in terms of "reality" at the
resolution of tissues, without getting bogged down in cells.

When discussing populations, we think in terms of "reality" at the
resolution of individual organisms, without getting bogged down in tissues.

When discussing species, we think in terms of "reality" at the resolution of
populations, without getting bogged down in individual organisms.

So, it naturally follows, then, that when discussing clades and associated
patterns of evolution and phylogeny, we think in terms of "reality" at the
resolution of species, without getting bogged down in any of the
finer-resolution units. 

But here's what I see as the problem:  atoms, molecules, cells have very
discrete boundaries, with almost no dissention among the people doing the
discussion.  Thus, for each discussion at a given level of resolution, there
is very little quibbling about the definition of the units at the lower
level of resolution (I'm not so sure about subatomic particles and tissues
-- but these are both irrelevant to the current discussion).

For most of our discussions, and for most taxonomic groups, we have very
little ambiguity about units of individual organisms.  However, once we get
above the level of the individual organism, things become increasingly
ambiguous. Some people assert that populations can be defined reasonably
well, but I see them simply as being at the least-messy end of the
increasingly messy transition of populations through infraspecific clusters
through species and on to higher levels of classification.

My point is this: If we want to have a meaningful discussion at some level
of resolution, then we end up spinning in circles if we are not basing our
discussions on well-defined units at the finer level of resolution.  Because
"species" (and I would argue "populations" as well) are so dramatically
less-well defined than units such as atoms, molecules, cells, and (in most
cases) individual organisms, we are somewhat handicapped when we want to
discuss phylogenies and evolution.

I am NOT suggesting that all discussions on evolution, phylogeny, etc.
necessarily need to fall back to the resolution of individual organisms
(although, in the case of cladistics, they ultimately do by default, because
characters -- whether morphological or molecular -- are observed on
individual organisms).  If I felt the notion of "species" (and other ranks
of taxonomy, both higher and lower) were useless, I SURE as hell wouldn't be
a practicing alpha-level taxonomist!

Rather, the crux of the "reality of species" issue has more to do with how
we construct inferences and extrapolations from our taxonomic analyses.  If
we fall into the trap of assuming "species" to be as "real" as organisms,
molecules, atoms, etc., we run the risk of losing site of what it is we are
actually studying.

Just one more point here on the "reality" (or not) of individual organisms:
the imprecision of this particular unit of biological nature is, in my
estimation, the basis for the discrepancy we sometimes see between
phylogenies of genes (resolution of the molecule), and phylogenies of
"species".

> I consider species to be real because I (used to) study their 
> origins. 
> As I pointed out to Tom, that would be pretty silly if 
> species were imaginary. 

I was going to respond to this, but then Jim Croft's message beat me to it
(and articulated my response better than I would).  *Obviously* I see the
utility of "species", and as such I think it's fallacious to interpret "not
real" as equivalent to "imaginary".  My point is that, when discussing
evolution and phylogenies, the meaningful level of "reality" is at the
resolution of individual organisms (show me some individual organisms of
leprechauns, and I'll define a useful species concept for them).
Populations and species and other such clusters are incredibly useful to
facilitate our discussions in truly meaningful ways.  But that doesn't mean
(in my mind, anyway) that they have any degree of objective "existence"
outside of our own minds.

> And I consider the fuzzy parts to be the most interesting. 

As do I!!  Which is why I direct my intellectual attention in that
direction.

> Despite there being a lot more tools for studying these 
> things, such studies are less popular that they used to be. 
> But the questions are still out there.

Amen to that!

Aloha,
Rich






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