The nature of cladistics [...]

Curtis Clark jcclark-lists at EARTHLINK.NET
Fri Nov 19 17:39:47 CST 2004


on 2004-11-19 08:50 pierre deleporte wrote:
> Thanks for specifying what you have in mind.
> My tentative comment in the text below.

Rather than deal with each of these, I will simply claim that they are
all molecular, along with the rest of population genetics. I'll deny the
existence of emergent phenomena, and the huff in indignation when a
physicist claims that all "molecular" processes are really subatomic.

> It's not because it is a human historical construct thait it is not a
> perfectly relevant one, a very likely reconstruction of what really
> happened. I'm deeply convinced that historical science demonstrated that
> pterausaurs existed, and exist no more. But they existed as individuals
> and populations.

I'm not interested in taking apart the ideas of "individual" and
"population" to demostrate that they have no real existence in nature,
but there are people who would do that. I'm naturally suspicious of any
argument based on "the level I study is real, and all the rest is a
construct."

> The point in debate is that this does not make
> "reptiles through the ages" a real thing. It's a set of real things
> materially disconnected in space and time,

Unless one believes in spontaneous generation, the set of organisms in a
lineage is hardly disconnected.

> Interestingly, the property of being
> winged may have contributed to some common fate for different
> pterausaurian individuals and populations, but not the fact of
> "belonging to the same clade" in itself (this is a classificatory notion).

You misconstrue. There are no pterosaurs because the extinction rate of
that clade exceeded its speciation rate. One can attribute that to
features of individual pterosaur species. That in turn can be attributed
perhaps to the dynamics of pterosaur populations, and that in turn to
the behavior of individual pterosaurs, which might well result from
their brain chemistry, which gets us back to molecules.

Reductionism is a useful tool. But it isn't the only tool.

> The 'clade birds' does not change (does it?).

(Looks outside to see if teratorns are flying overhead. Negative.) I
think there is evidence that it does.

> I
> simply suggest than we can do that  without reifying clades and lineages
> and attributing them processes "at their level", when in fact we mean
> that some common features may cause the same effects.

Molecular biologists might very well say that you are "reifying"
individuals and populations. I don't find that whole approach at all useful.

> but convergence can do the trict the same way, can't it? If all big
> flying critters undergo extinction in some environmental context, does
> it matter that you "are a pterausaur" at all? Extinction is an
> individual and populational, ecological process of natural selection,
> not a "phylogenetic" one properly.

When the last member of a clade dies, the clade is extinct. The
biosphere is deprived of that lineage, and all the things that made it
unique. That hardly seems like a "construct" to me.


--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062




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