Continuity, reticulation, and classification

John R. Grehan jrg13 at PSU.EDU
Tue Jul 24 11:25:25 CDT 2001


At 05:07 PM 7/23/01 -0500, you wrote:
>     Before getting back to viruses and gene evolution, I'll quickly address
>the "human construct" issue.  Any bioclassification is a construct and
>arbitrary.

If it is 'arbitrary' does this mean that it has no predictive value about
the nature of reality? If not then arguments over classification are
rendered pointless.


>There is no real beginning or end to any species (especially when time is
>considered as well as space).  The tree of life is a continuity, and any
>cuts to divide it into taxa are arbitrary.

Depending on what one may mean by arbitrary. There is a continuity between
myself and my parents, but a specific event may be identified to specify my
individuality. Perhaps selection of that event is 'arbitrary' but the
resulting designation is not (at lease I perceive a separate existence from
my parents, as they do me).

>Cladistic classification is just
>as arbitrary in a different way, and many cladists believe that sister
>groups actually exist (which I find very troubling).

I'm not aware of 'troubling' being a criterion for the reality of something.

>Its benefits are
>marginal at best, and the drawbacks just keep getting more and more
>apparent.

In biogeography at least, cladistic techniques have been more than marginal
in helping to provide a more precise resolution of character geography.

>     Anyway, reticulation is just one more reason strictly cladistic
>classification fails to reflect the reality of evolutionary history.

But it can present potentially informative statements about the nature of
reticulation.
This was demonstrated by Craw (1983) for biogeographic analysis.

  However, strictly cladistic
>classification will most clearly betray its fundamental weaknesses (and
>overly simplistic underpinnings)

Perhaps all techniques have fundamental weaknesses?

  But a hybrid system will
>allow some measure of stability over a wide range of detail---from the broad
>evolution of organisms at kingdom and phylum levels down to minute details
>of genetic variation among individuals.


It seems to me that the overall theme for this system is utility, and it
seems to me that utility is the hallmark of the arbitrary.

John




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