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I have read the many postings regarding speciation, and I was
happy to find that my lay understanding of the question seems
to agree well with that of the learned posters (is that the right
noun?). I would only like to point out three perhaps piddling
1. The biological and the phylogenetical species concepts are
of course two aspects of the same thing; the difference arises
only when you decide to regard that thing crosswise (in the
present, synchronically) or lengthwise (historically,
diacronically, to speak Structuralese). For reproductive
isolation is of course what keeps the descendants of a
historically split species apart; and as we are not all-seeing
and also not simultaneously present in all geological epochs, we
can only infer a historical splitting or branching ex post facto,
by observing a case of isolation, or by concluding that the
isolation must exist because of the striking dissimilarities of
the two groups.
2. So obviously there exists another species concept, the
typological. And this is of course the original one. It is even
older than Aristotle and Platonic essentialism. It is what
every pre-scientific human being has used since our
ancestors began to name the things on the face of the earth.
And, incidentally, this is what paleontologists are forced to
use, because even they cannot observe the actual splitting
event, and, as somebody noted, "fossils do not copulate".
So you have to select and agree upon certain distinctive
traits and base your typology on them.
And here enter not only chance, but also subjectivity. Chance:
you can only use traits that fossilize. They are in all instances
secondary, i.e. phenotypical, not genotypical. They may not
even be really important differences. They just happen to be
observable. So our (essentially metaphysical) drive to sort,
label or/and be damned drives us further than common sense
perhaps should permit us to go. Subjectivity: In one of his
satires, Strindberg tells us of a buttonologist whose calling it
is to construct a taxonomy of disciform vestment-fastening
devices. He classified them by their holes: buttons with two
holes, buttons without two holes, buttons with four holes,
buttons without four holes... and so forth. But he could just as
well have sorted them by material, or colour, or whatever.
Most of the disputes in fossil taxonomy seems to arise from the
question of choice of traits. And there is no obviously TRUE or
RIGHT choice. It is a matter of convenience---unless you are
a late-born Platonic essentialist of course.
3. Both the biological and the phylogenetic concepts are quite
impossible to apply to groups that do not reproduce sexually.
Bacteria for instance: they swap genes in a promiscuous
manner calculated to arouse the indignation of mr Helms
and the rest of the right-thinking majority. As we cannot
observe any reproductive isolation, we find it difficult to make
any conclusions about evolutionary branchings, except the most
gross ones. We are thrown back on typology: shape, Gram
colouring etc. And this goes for many plants too: look at the mess
which is subsumed under "Rubus sp." This is really the case
with the domestic dog even. Not only can all doggies have puppies
with each other---yes, even a great dane and a chihuahua, albeit
indirecly, say with an alsatian and a beagle as intermediaries
---the genetic pool labeled "dogs" (Canis familiaris) can
exchange AND DOES exchange genes with that labeled "wolves" (C.
lupus). So biologically, they are one species. The reason why
your poodle has a different taxon name than the grey wolf is
really historical: the biological species concept is so young that
we have not got around to drawing the conclusions yet.
Still, it it heartening to observe that any sane Bushman or
Eskimo agrees with any sane taxonomist on the question which
kind of critter, is, or is not, a distinct species. At least when they
classify vertebrates or higher plants. We are obviously observing
roughly the same thing, even if look at it differently.
(lexicographer ... "a harmless drudge" according to Dr. Johnson,
so bear with me)
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