[Taxacom] Classification of ALL life forms?

Kenneth Kinman kennethkinman at webtv.net
Wed Apr 21 21:57:26 CDT 2010


Dear All,
       The relatively new overall classification of life (2005) by Peter
Ward has apparently not attracted a lot of attention or support, which
is a very good thing in my opinion, because I don't think the newly
proposed taxa are particularly natural or useful.  Actually I only
stumbled across it today for the first time.            
       I do agree with him that RNA life preceded present-day DNA-based
life, and also agree with him that viruses should be classified as
"life", even if all present-day viruses are probably parasitic.
However, his classification has a lot of problems:
      (1) There is no evidence that cellular RNA forms (his Domain
Ribosea) ever existed.  Seems more likely that a precellular RNA world
evolved into a precellular RNA-DNA world before becoming cellularized
into the obcells (of Cavalier-Smith) or other kinds of protocells.  We
may be able to synthesize cellular RNA forms in the future, but giving
such freaks of nature a separate Domain is based on the totally
unsubstantiated assumption that DNA evolved after cellularization of
primitive life.
      (2)  I also see no advantage in dividing viruses between two
high-level taxa (his Dominions Ribosa and Terroa).  Some present-day,
non-cellular RNA viruses may well be just as derived as non-cellular DNA
viruses).  All types of viruses may have been popping in and out of
genomes for billions of years, so whether you regard viruses as living
or not, it is a polyphyletic grouping no matter how you classify them.              
      (3)  Most importantly, if the RNA world preceded the DNA world,
and Peter Ward and agree on that, his Dominion Ribosa is not only
paraphyletic, but paraphyletic in a highly asymmetric (and unuseful)
way.   So I see this new high-level classification as overly asymmetric,
unuseful, and as discussed above, probably unnatural.  Therefore the new
taxonomic category Dominion seems both unnecessary and extremely
problematic.
       Finally, his proposal that Dominions Ribosa and Terroa be
combined into a single taxonomic category (Arborea) for earth-based life
is unneeded.  He not only failed to name the earth-based taxon of rank
Arborea, I proposed a same taxonomic category back in 1994, named
Cosmogenre, and gave earth-based life the specific name Cosmogenre
Geobiota.  I also proposed calling all non-Earth-based life under the
umbrella term Cosmogenre Exobiota until specific such life forms were
discovered and described.  If you regard the supposed Martian "fossils"
found in Antarctica as independently evolved forms of life, I suggested
that you could perhaps call them Cosmogenre Martiobiota, but I am
skeptical about these supposed "fossils", so perhaps it is best to wait
until paleontologists find fossils on Mars (in situ on that planet), a
couple of decades from now.
       In any case, I still prefer classifying viruses and progenotes in
taxon Parabacteria.  Whether you want to call it a separate Domain or
Kingdom is one thing, but I find the new higher-level taxonomic category
(Dominion) neither natural nor useful.  Instead it seems even more
unnatural and problematic than Woese's Domains.  In both cases, there
seems to be an implication that they reflect holophyletic taxa (clades)
when there is no credible evidence to back it up.  Such cladification at
the highest level is more harmful than helpful.  Frankly, I see them as
simplistic, deadend, classifications which divert us from a true
understanding of the early evolution of life.  It is strict
cladification prematurely run amok (amuck) and is not only unhelpful,
but harmful in the long run.  I think Peter Ward should be more
skeptical of Woese's views.  It is best to recognize paraphyly where it
clearly exists (and is extremely useful) and stop pretending (and
simplistically ignoring) that such paraphyly is not only useful, but a
fundamental expression of how the true Tree of Life actually evolved.
Even if you don't buy this at the species level, it is abundantly clear
at broader (especially Kingdom) levels.             
       ------------Ken Kinman              

Ward's overall classification of earth-based life:

Dominion Ribosa (RNA life)
      Domain Viroea (non-cellular RNA viruses)
      Domain Ribosea (theoretical, cellular RNA forms)
Dominion Terroa (RNA-DNA life) 
      most Earth life (including some viruses)

     NOTE: It is unclear to me if he would put such Terroa viruses in a
separate Domain from Woese's Three Domains.  In any case, the basal
Domains of Terroa are almost certainly  paraphyletic, not holophyletic
(strictly cladistic).  The only Domain that is clearly holophyletic is
Eukaryota.  I don't find either the proposed phylogeny or the name
"Terroa" (a real clade??) particularly helpful.  Paraphyletic taxa are
clearly useful in my opinion, but pretending that such paraphyletic taxa
are holophyletic (strictly monophyletic) is extremely problematic,
especially at such high levels of biological classifications.






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