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From: chi9@quads.uchicago.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio,sci.chem
Subject: Re: "Primitive" != Unevolved (was Re: Forgotten Entities...)
Message-ID: <1990Nov6.043039.13166@midway.uchicago.edu>
Date: 6 Nov 90 04:30:39 GMT
References: <4578@husc6.harvard.edu> <90307.154236JAHAYES@MIAMIU.BITNET>
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Organization: Department of Biology at the University of Chicago
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In article <90307.154236JAHAYES@MIAMIU.BITNET> JAHAYES@MIAMIU.BITNET (Josh
Hayes) writes:
>With respect to apparently primitive critters in vent communities
>and such. This is a bugaboo that I run into in my intro bio courses
>all the time; there is this idea that phylogenetically "primitive"
>organisms somehow stopped evolving when they arose...[. . .]
>               [. . .] Sharks, archaebacteria, sponges, humans,
>that we see around us today, are all equally primitive and all
>equally highly-evolved. [. . .]

	This is partly true, but not 100% true.  While it is highly unlikely
that any extant organisms have STOPPED evolving, it has become fairly obvious
from doing molecular phylogeny that not all organisms evolve at the same rate.
The high thermophiles (so far all archaebacteria and eubacteria) have been
evolving slowly; mycoplasmas evolve rapidly (thus, their lack of complexity is
degenerate, not primitive); all of the known eukaryotes evolve rapidly;
microsporidia and Giardia and its relatives evolve very rapidly; and
mitochondria and chloroplasts evolve at superspeed.  Many references on this
are available -- the best ones that I can think of right off hand are Carl
Woese's articles in a 1987 issue of _Microbiological Reviews_ and in a June
(+ or - a month) 1990 issue of _Proceedings of the National Academy of
Sciences_ and a reference (don't remember author's names off hand) in the
latter article about how to root a tree using duplicated genes.  I also have
other references at home if you are interested.

	The moral of this is that the various organisms are NOT all equally
primitive or equally highly-evolved.

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