🚀 go-pugleaf

This thread does not seem to have picked up any chemistry, so I have directed
followups to sci.bio.

In article <4618@husc6.harvard.edu> Ellington@Frodo.MGH.Harvard.EDU (Deaddog)
writes:
>Well said!
>However, I think that the previous responses by Drs. Chiaraviglio and 
                                                 ^^^^
>Yanega (like chemical companies, I find it simplest to assume everyone is 
>a Dr.; no disrespect intended)

	Unfortunately, not until a few years in the future. . . :-P

>                               were more subtle than "thermophilic 
>archaebacteria stopped evolving."

	Yes, as I explained in a couple of previous posts, what I was trying
to say was about slowly-evolving, deeply-diverging (with respect to main
trunk(s) of closest primary lineage), thermophilic organisms.

>                                   I believe the central issues are 
>(1) Has one deeply-branched lineage of archaebacteria evolved MORE SLOWLY 
>(i.e., adopted fewer metabolic or physiological changes over the course of 
>time) than other organisms?  (Obliquely, this applies to the bees as well; 
>that is, can a lineage evolve slowly relative to other lineages.)

	Yes.  What Carl Woese calls the Crenarchaeota (in his recent _Proc.
Natl. Acad. Sci._ article) fits this description, as does the "genus"
Thermococcus (probably more appropriately defines a kingdom) in what Carl
Woese calls the Euryarchaeota, which also includes Archaeoglobus, the three
(or more) Methanogen kingdoms, and some non-methanogenic organisms derived
from the Methanogens (Thermoplasma and the Extreme Halophilic
Archaebacteria).  Within the latter groups, which branch from the
Euryarchaeote main sub-lineage, the more deeply-diverging kingdoms tend to be
more slowly-evolving (except Thermoplasma, which isn't that much of a
thermophile anyway) and contain members whose optimum and maximum growth
temperatures are higher -- by a considerable margin (up to around 90`C maximum
last time I looked for the Methanococcus kingdom as opposed to around 55`C to
65`C for the kingdom composed of the more highly-evolved Methanomicrobiales,
for instance).  The same pattern is also apparent within the Crenarchaeota, of
which the fastest-evolving "genus," Sulfolobus, is also the one capable of
growing at the lowest temperatures (however, being able to grow in and even
use oxygen may also be a factor in its more rapid evolution, but this does not
seem to be a factor among the Gram-positive Eubacteria, for which this
possibility has been investigated).

	A similar but substantially muddier picture exists for the Eubacteria.
Unfortunately, no such picture or refutation thereof exists for the
Eukaryotes, because

	1.  The deepest-diverging members of the Eukaryotes are not
	    very deep divergers when one takes into account the total
	    amount of evolution the Eukaryotes have undergone since
	    splitting off from the Archaebacteria

	2.  The deepest-diverging members of the Eukaryotes, the
	    Microsporidia and Giardia and its relatives, have been
	    evolving even more rapidly than the other Eukaryotes
	    characterized by molecular phylogeny, and the next-deepest
	    divergers, the Trypanosomes and their relatives, have also
	    been logging evolutionary distance pretty rapidly.

	3.  No high thermophiles have been found among the Eukaryotes.
	    The best Eukaryotic thermophiles only grow at up to about
	    60`C (give or take ~2`C), and these ones of these for which
	    the molecular phylogeny has been done have been shown to
	    have evolved from mesophilic groups.

>(2) If so, does this imply that the ancient forebear to these organisms 
>has characteristics similar to the modern versions?  (I don't believe that 
>(2) necessarily follows from (1), since both questions involve the rather 
>complex question of what constitutes a 'trait' and whether all 'traits' 
>are equal.)

	You are right that (1) does not prove (2).  However, it lends
considerable credence to (2), since it is unlikely that several slowly-
evolving lineages which diverged from each other long ago will have undergone
great phenotypic changes relative to each other.

>Nevertheless, I could not have summarized the argument against "frozen 
>evolution" better than you did.

	[That refers to a poster following up one of my articles.]  I never
said anything about "frozen evolution."  What I have talked about is rates of
evolution which differ considerably, as outlined in a previous message.

--
|   Lucius Chiaraviglio    |    Internet:  chi9@midway.uchicago.edu