Re: Species [arbitrary to a degree]

["Jaime A. Headden" <qilongia@yahoo.com>]

  David Marjanovic (david.marjanovic@gmx.at) wrote:

<BTW, I've learned today that the bacteriologists who can't use biospecies have 
taken the
morphospecies to the logical extreme, _they have invented a specificometer and 
a genericometer_:
Stems belong to the same species if they don't differ in G + C content by more 
than 5 mol%, and to
the same genus if they don't differ by more than 10 mol%. This is immensely 
practical* because
whether 2 bacteria belong to the same species or genus has become testable. But 
I'd be a bit
surprised should it turn out that this idea could be extended to eukaryotes 
respectively to known
biospecies.>

  While testable, this is still doubly arbitrary. The assumption that a genus 
has any sort of
fundamental difference from a species, as if a genus has any reality or, for 
that matter, a
species, being one of them. The other is the cut-off point for what can or 
cannot be a congenetic
or conspecific bacterium. It should also be made clear that rates of evolution 
have changed, and
bacteria show much more variation within the whole than do the entire 
Eukaryota, are much more
plentiful, and populations of a group can quite easily take on genetic 
information from other
bacteria, befuddling true phylogenetics into just a percentile genome variance 
issue. Population
stability is not something easily found in either archaean or bacterian or 
basal eukaryotan
organisms. The higher eukaryotes appear to have developed a stability regime in 
their genome that
prevents most accidental transcription or lateral gene transfer. Suggestive 
that what might work
with bacteria (and I'm not saying it doesn't, but that's what it looks like) 
would probably _not_
work with eukaryotes, higher eukaryotes, etc.


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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