pierre.deleporte at UNIV-RENNES1.FR
Tue Apr 20 18:43:17 CDT 2004
Starting back from the original question:
At 22:11 13/04/2004 -1000, Richard Pyle wrote :
>The more specific question that I'm interested in is whether
>boundaries between species actually exist in nature (independent of our
>ability to observe them) and it is our job to discover them; or such
>boundaries are (artificially) defined by us as a means to allow more
Individuals are rather well circumscribed biological systems in themselves.
Classic species are classes of individuals. Species themselves are not
"individuals". They are not even loosely connected biological systems (the
dead individuals don't interact with the living ones, to the difference
with spatially restricted populations composed of living, interacting
individuals). Classic subspecies also are such kinds of classes and don't
form a coherent interacting system (the dead members of a subspecies don't
interact with the living ones, contrary to living members of an existing
population). (possible reading on this: Mahner and Bunge 1997).
According to Popper (which cannot be always wrong ! ;-), all
classifications are conventional. A species (or subspecies) is a terminal
taxon = a "class" of some kind. Its delineation depends on your convention
rules for delineating (sub)species.
Just define (sub)species a useful way, according to your problem at stake
(evolutionary, or other...).
Seems all trivial... What is required is at least to expose clearly your
criteria (which species concept you're using in a given context)... seems
it's not traditionally done (see other posts).
This said, it is not because you have a clear criterion (or unambiguously
combinable series of criteria) that species limits will not sometimes
appear fuzzy in the real world (see other posts). This is "real" too: the
easiness with which natural features will fit (or not well fit) into your
conventional classification grid. Part of the explanation is the ongoing
evolutionary process, and possibly "speciation" process, which is
progressive in populations and biotas (see many other posts).
Thus, OK with Richard's hint that species "boundaries are (artificially)
defined by us as a means to allow more effective communication". And
"effective communication" (hence relevant criteria) may change according to
different questions at stake. Classification implements useful conventions
Some will call "real species" the classes of individuals fitting
unambiguously their classification criteria; they rather should be called
"well discriminated species" according to these particular criteria.
Example: suppose you have a population of elephants. You may class it into
a species, and possibly a subspecies (...your criteria, for your specific
purposes). Two pink mutants occur in this population.
- if your problem is regional conservation biology, you can simply go on
calling this a population: all the local living elephants, including the
pink ones (i.e. you don't propose to shoot them down in order to preserve
the "original species" unspoiled, neither to breed them separately in order
to try to create a "new species"). Newborns join the population (even if
pink), dead ones quit it (even if grey).
- now if your problem is evolutionary biology and speciation processes,
it's interesting to distinguish the pink individuals as the first members
of a possible new (sub)species. If you mix up the pink ones with their
colleagues because they belong to the same population, you can't easily
engage into the analysis of the possible speciation process (i.e. follow
the particular fate of the pink elephant's descent). Evolutionary studies
must account for the apparition and fate of novelty. Hence some
'typological' classification is, paradoxically enough, useful for
evolutionary investigations: how do new "types" appear, and succeed or are
wiped out, or coexist in the long run with ancient types. If you have a
definition of "species" (or whatever way you decide to name your terminal
classes) which means "lineage" or "sympatry" (or both) whatever the changes
in "types", you cannot easily study what is classically called "speciation"
(= a process of divergent evolution).
- other question: an extreme proposition for phylogenetic analysis is to
use individuals as terminal taxa. Seems it should work. Certainly for
clonally reproducing organisms. And likely for other ones too (you simply
expect fuzziness in the "tokogenetic" apical zone of the tree... and some
extra computing time!).
Hence classifications and their corresponding classes are not "real or not
real" (they exist from the moment we forge them), they are "useful or not
useful" in a specified context, and classes or real objects appear more or
less well discriminated, this possible fuzziness being itself a possible
source of further investigation. Different problems, different optimal
classifications (criteria and delineation rules...), and this vails for,
let's say... terminal taxa of all imaginable kinds and names, defined for
optimal communication in specific contexts.
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