Woese art., archaebact.

Andrew J. Roger aroger at is.dal.ca
Sat Aug 31 09:49:55 EST 1996


David Faguy, Ph.D. wrote:

> However, I
> don't think anyone could say that M. jannaschii is close to the (last) common
> ancestor.  It is exactly (in real time) the same 'distance' from the last common
> ancestor as you or I. The genome sequence  may (or may not) have evolved at
> a faster rate. In any case, M. jannaschii is very different from what the LCA could
> have been like.
> Sorry if I sound overly didactic, but when people talk about the archaea as 'ancient'
> or 'primitive' it bothers me.


You couldn't be more correct. I have no idea why this mythology persists.
The name "Archaea" means ancient. Its derived from "Archaebacteria" which
was the original name that Woese gave them when he thought that the three
domains were all separately derived from a primitive progenote. At that time
there was some speculation that Archaebacteria were closest phenetically to
the LCA. In the early 90's Woese turned it around and endorsed the view
that Archaebacteria are an immediate sister group to eukaryotes. At this
time the peculiarities of Archaes not shared by eukaryotes and Eubacteria 
started to look like autapomorphies (such as the isoprenoid ether-linked
lipids in their membranes). So how the hell do characteristics like these get
turned around again to be "ancient"? 

It is utterly vague propaganda which tries to elevate the importance of
the Archaebacteria (I personally think they are very important but not
for silly reasons like this).

I think that if this kinda stuff keeps appearing we should start calling
them the "We-hold-the-key-to-every-major-evolutionary-transition-bacteria".
Either they share derived characters with eukaryotes and they are not ancestral
or both eukaryotes and archaes have the ancestral state and its the
eubacteria that are the derived ones. The things unique to archaebacteria
are LEAST likely to be characters found in the LCA if we accept the following
topology of the universal tree:

(Eubacteria,(Archaebacteria,Eukaryotes))

I am guessing that part of this BS comes from the idea that many archaes
are thermophiles and many people think that the LCA was also a thermophile.
But then why would archaebacterial thermophiles look more like the LCA than
eubacterial ones (e.g. Thermotoga, Aquifex, Thermus etc.)?  

Answer: there is no reason at all to think this.

Sorry for this unprovoked attack at nobody in particular but it bugs
me too.

Cheers
Andrew Roger
aroger at is2.dal.ca
Dept. of Biochemistry
Dalhousie University
Halifax NS
TEL: 902 494 3569
FAX: 902 494 1355

PS- did anyone see the New York Times, Friday August 23,96 article
on the Methanococcus genome? This contains more BS than anything
I've seen before. In fact, it is probably the most misleading
but at the same time vacuous article I have read about the subject
of Archaebacteria.



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