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From: Ellington@Frodo.MGH.Harvard.EDU (Deaddog)
Newsgroups: sci.bio,sci.chem
Subject: Re: Forgotten Entities: Do You Remember Any?
Message-ID: <4578@husc6.harvard.edu>
Date: 1 Nov 90 19:27:57 GMT
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Organization: Molecular Biology, Mass. General Hospital
Lines: 39
References:<1990Oct25.232546.12357@portia.Stanford.EDU> <1990Oct26.072420.28005@cec1.wustl.edu> <90300.133611JAHAYES@MIAMIU.BITNET> <1990Oct30.030717.8923@midway.uchicago.edu>

In article <1990Oct30.030717.8923@midway.uchicago.edu> 
chi9@quads.uchicago.edu (Lucius Chiaraviglio) writes:
> combination of slow evolution and deep phylogenetic divergence,
> which -- when the deeply-diverging organisms have a lot in common
> phenotypically, which they do -- implies greater resemblence to ancestral
> forms of life.
   This is somewhat disturbing.  
   First, isn't the fact that only a few, deep phylogenetic divergences 
have been found between the *known* Archaebacteria a function of the 
relatively small number that have been catalogued?  Wouldn't you say 
exactly the same thing if only one Gram-positive and one Gram-negative 
organism was known in the eubacterial ur-kingdom?  As the Archaebacteria 
lineage is fleshed out, I believe that intermediate forms will show up 
along all the branches (this is already true for the sulfur-utilizing 
Archaebacteria).
   Second, while the Archaebacteria have some traits in common, their 
phenotypic resemblances are immaterial to what a primitive life form looks 
like; it is only  those traits that are held in common by each of the 
three ur-kingdoms (or at least two out of three) that give us a logically 
valid picture of the common ancestor of modern life (what I like to call 
the progenote, but Woese has disagreed).  Also, what makes you think that 
Archaebacteria are more phenotypically similar within their ur-kingdom 
than eukaryotes or eubacteria; what traits are you referring to?
   Finally, the idea that the evolutionary rate of archaebacteria has been 
slow seems unsupported:  aren't the ribosomal RNA sequences within the 
archaebacterial lineage at least as divergent from each other as those 
within the eubacterial or eukaryotic lineages?  Doesn't the wide variety 
of metabolic adaptations seen for different archaebacteria (halophiles, 
thermophiles, acidophiles, chemolithotrophs, chemoautotrophs) demonstrate 
that the rate of evolution has been at least as quick as in the other 
lineages?
   I may be misreading your intent, but it seems as though you want to 
classify archaebacteria as 'living fossils'--and there just ain't such a 
thing.
A.E. 

Dept. Mol. Biol.
Mass. General Hospital
Non-woof