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

Curtis Clark jcclark-lists at earthlink.net
Sun Sep 14 22:55:06 CDT 2008


On 2008-09-14 16:11, Richard Pyle wrote:
> 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. 

Exactly.

> 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).

I'll ignore all but cells, since atoms and molecules don't have 
ancestor-descendant relationships in the same sense as cells, 
individuals, and species....

> 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.

The span of a human lifetime relative to an average mitosis is immense, 
but relative to an average speciation event is minuscule. If our lives 
were measured in milliseconds, perhaps mitosis might seem a vague, 
fuzzy, and disconcerting process.

> 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.

Indeed. To quote a colleague, "If it were easy, everyone would be doing 
it." But I see it as a challenge, not as a fatal flaw.

> 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). 

Alas.

> 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.

This is where our views seem to diverge. I can accept that there are 
real species without needing to accept that I know what they are. 
Certainly if I were looking at an aspen tree and thinking that it were 
an individual, totally ignorant of the fact that the entire hillside of 
aspen trees is an individual, that only speaks to my lack of 
understanding of the situation, not to any unreality of "individual" as 
a level of organization.

> *Obviously* I see the
> utility of "species", and as such I think it's fallacious to interpret "not
> real" as equivalent to "imaginary". 

Try convincing a mathematician of that wrt numbers.

> 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).

What if they are fuzzy? :-)

> 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.

With no intention of following the metaphysical path, objective 
existence is a slippery thing. Science can be understood totally in the 
realm of mental models: we make mental models, formulate hypotheses, 
test the hypotheses against our sensory inputs (and all that technology 
still has to funnel through our senses), and compare with our mental 
models of the mental models of other scientists. To the extent that it 
all agrees, it's "consensus reality". In that sense, species are as real 
as any other mental model as long as they are useful.

-- 
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Director, I&IT Web Development                   +1 909 979 6371
University Web Coordinator, Cal Poly Pomona




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