classifying life ("primitiveness")

Wed Apr 19 08:05:32 CDT 2000

Brian,
     First, let me assure you that I do not base my
theories upon Schopf's "cyanobacterial" fossils (although the morphological
similarities are remarkable, and I do believe that they are primitive
cyanobacteria).  It would
certainly be naive and simplistic of me to do that.  More
on that below.
     And I certainly would not strongly object to dividing
Monera into two Kingdoms if we had the knowledge to do so.
But I don't even like the new Diderm-Monoderm dichotomy
(also called Negibacteria-Unibacteria dichotomy), even
though this would be somewhat preferable to Woese's
classification and nomenclature.  Even Cavalier-Smith (one
of the most brilliant evolutionary biologists alive today)
had the sense to return to single Kingdom of prokaryotes
(although he prefers to call it Kingdom Bacteria rather
than Kingdom Monera).  He has now downgraded "Archaebacteria" (=
Metabacteria) two steps from a Kingdom to an Infrakingdom.  This is still
very inflated in my opinion, but certainly far less than Woese.
      I still think one Kingdom Monera with 4 Phyla (or
more?) is preferable.  Having looked at it from both
microbiological and zoological perspectives in my career,
there are great many ways to measure diversity (genetic,
metabolic, developmental, etc., as well as morphological
and species diversity).   Without balance, taxonomic
inflation would probably lead to Kingdoms Arthropoda and
Chordata (seriously, if someone hasn't done this yet, someone will
eventually, mark my words).  Choosing Three Domains over Five Kingdoms is
the currently popular thing to do (especially on the Internet), but one
should not assume that those who reject Three Domains are all out-of-date or
stuck in an old rut.
     My ideas on the early evolution of prokaryotes, which
are still evolving and being refined, are based on
metabolic pathways, Woese's own rRNA data, the structure and chemistry of
cell membranes, evolution of photosynthesis, and a lot of other things.  I
certainly do not agree with some of the ideas being put forward by
Cavalier-Smith, Gupta, Lake, Margulis, Mayr, and many others who are also at
odds with Woese's rather simplistic approach, but at least they are trying
to look at and incorporate a broader range of evidence.
     I certainly cannot expect anyone to presently accept
my theory that primitive Cyanobacteria (much simpler than
modern forms) were the first forms of cellular life on
Earth.  There are still too many missing pieces to this
puzzle, and I do not have the resources to piece them
together any faster than I am trying to do.
     But even if early cellular life was not
cyanobacterial, there is not a doubt in my mind that they
were eubacterial and non-thermophilic (probably mesophilic, but possibly
even psychrophilic).  I believe that Woese's
ideas are totally offbase, and the idea that early life was  thermophilic is
total nonsense.  I am certainly not alone
in that opinion, although I will admit that I am presently
pretty much alone in discussing (at least publicly) a
cyanobacterial origin of life.  What amazes me is that other critics of
Woese (and there are many) are still being taken in by his thermophilic
rooting of Eubacteria, but it certainly partially explains why they do not
take seriously the notion that Cyanobacteria could be very close to the base
of the Tree of Life.  So it goes.
                           ---------Ken Kinman
P.S.  Obviously a given species of fish (or even a bacterial species) can be
younger than a given species of mammal.  I am talking about broad crown
taxa.  And if Woese contends that prokaryotes should be classified higher
taxonomically just because they have been around longer, that doesn't hold
water for me.
      Classifying a single Kingdom Monera and multiple Kingdoms of
eukaryotes is rather similar to classifying a single Class Amphibia and
multiple classes of amniotes (reptiles, birds, and mammals).  Of course,
strict cladists hate this because Monera and Amphibia are paraphyletic.  But
in the Kinman System, an appropriately placed marker for the Eukaryota
(within Kingdom Monera) should hopefully assuage some of their paraphyletic
Angst.  And hopefully this also answers Brian's question about not
classifying eukaryotes in Monera---by using such "cross-referencing"
markers, I do show the origins of eukaryotic host cell (and organelles as
well) within Kingdom Monera.
     Anyway, trying to couple geological age and rank of a taxon is
obviously futile.  I'm tempted to discussing anagensis and the vast
differences in molecular "clocks" in different taxa and at different times,
but that is another "can of worms".  Suffice it to say that I personally
believe cyanobacteria generally have the slowest molecular clocks of any
form of life still extant.  ---K.E.K.
*********************************************************

>From: "B. J. Tindall" <bti at DSMZ.DE>
>Reply-To: "B. J. Tindall" <bti at DSMZ.DE>
>To: TAXACOM at USOBI.ORG
>Subject: classifying life ("primitiveness")
>Date: Wed, 19 Apr 2000 10:32:20 +0200
>
>Just a few comments on what Ken Kinman wrote. Okay the
definition of
>primitive is not the way that I thought you might be using
it and in
>context that appears to be suitable. However, it would
start splitting
>hairs about what was the ancestor of what. If we take
eukaryotic organelles
>as an example (mitochondria, chloroplasts, etc.) then I
would say that
>ancestor of modern day prokaryotes are the ancestors of
these organelles.
>
>In quoting the time scale for the evolution of bacteria
"Metabacteria" I
>would assume that the "early" date is based on
"cyanobacterial" fossils. I
>would just like to raise the point that these fossils are
considered to be
>cyanobacteria based on morphology. There would appear to
be no evidence
>that they contained photosynthetically active pigments.
Morphologically it
>would not be easy to distinguish some of the filamentous
gliding
>cyanobacteria (e.g. Oscillatoria) and the large celled,
filamentous gliding
>bacteria, such as members of the genus Desulfonema (which
are anaerobic
>sulphate reducers and are not oxygenic phototrophs). Here
is see a danger
>of extrapolating from present day organisms back to
ancestors, without
>knowing much about the ancestors. In the case of
mitochondia and
>chloroplasts we do not know whether they became associated
with eukaryotes
>via a single, or multiple events. As for what came first,
ancestoral
>"bacteria" or ancestoral "archaebacteria" I do not know
because I was not
>there (c.f. D.Colless, "The phylogenetic fallacy"). Could
it be that these
>ancient fossils represent lineages which did not develop
further - the
>Burgess Oil Shale seems to provide evidence of such
effects in eukaryotes,
>so why should one not also have similar effects in
prokaryotes?
>
>I also think there is a big difference between the
ancestoral role of
>certain prokaryotes and the present day state of affairs.
My impression is
>that Woese has tried to emphasise the current diversity
which is why he
>wants more higher taxa within the prokaryotes. This is a
consequence of
>diversification over geological time, the longer one is
around, the more
>diversification, the more higher taxa (anyway that is what
I interpret from
>his work). This reminds me of a statement from Simpson
which, while
>acknowledging that Homo sapiens may have an amoeba as an
ancestor, he
>strictly rejected linking Homo sapiens with the amoeba.
While prokaryotes
>may have been around first I do not see that it is a
logical consequence of
>their early presence on Earth to restrict them to one
kingdom - but I am
>open for appropriate arguments.
>
>There is also a comment about secondary simplification of
organisms - this
>is certainly a point worth stressing, since one often gets
the impression
>that evolution always leads to more complex forms. I agree
with that point.
>
>If the origin of prokaryotes is so important in
restricting them to a
>single kingdom, then the chimera origin of eukaryotes
would suggest that
>they also have a (multiple) prokaryotic origin, but they
are not included
>in the prokaryotes? This is a question, not a statement.
>
>Are all crown taxa equally old? Good question. Probably
not, but I am not
>sure that this problem has been properly addressed. If we
assume the
>evolutionary sequence:
>fish->amphibians->reptiles->mammals
>then it is true that fishes can be found in the geological
record over a
>longer period of time than mammals. But does this mean
that a modern fish
>species is inherently older than a mammal species? Please
correct me if I
>am wrong, but is it not possible that a modern fish
species arose after a
>modern mammal species on a geological time scale? Thus,
the age of modern
>day taxa are not automatically coupled to the length time
over which their
>(first) ancestors have appeared in the older geological
record. We have
>examples of ancient or fast evolving bacterial taxa (e.g.
genera) which
>have simply been fragmented into several genera.
>More food for thought.
>Brian
>
>
>**********************************************************
**********
>* Dr.B.J.Tindall      E-MAIL bti at dsmz.de
        *
>* DSMZ-Deutsche Sammlung von Mikroorganismen und
Zellkulturen GmbH *
>* Mascheroder Weg 1b, D-38124 Braunschweig, Germany
        *
>* Tel.: ++ 531 2616 0 (general)
        *
>* Tel.: ++ 531 2616 224 (direct)
        *
>* Fax:  ++ 531 2616 418
        *
>* Fax:  ++ 531 2616 491 (ISDN)
        *
>*
        *
>* Homepage: http://www.dsmz.de/index.html
        *
>* E-MAIL: help at dsmz.de (general enquiries)
        *
>*         sales at dsmz.de (sales)
        *
>**********************************************************
*****
______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com