CYANOBACTERIA are ancient "Windows to the Past"
kinman at HOTMAIL.COM
Tue Dec 2 11:14:56 CST 1997
Although one must be very careful to distinguish between
plesiomorphies and apomorphies in so-called "living fossils", such
windows on the past are all around us. Although most modern
cyanobacteria display apomorphies that mask their fundamental
primitiveness, I believe they are the most significant "window on the
past" of life's cellular evolution.
And once Woese's "Three Domain" tree of life is challenged and
corrected, even the rRNA sequences of cyanobacteria will be seen as
primitive relicts of a considerable radiation of eubacterial groups that
preceded the origins of the Metabacteria("Archaea")-Eukaryote lineage by
many hundreds of millions of years.
I do not base this view on Schopf's fossil evidence of archaic
cyanobacteria, but it is certainly comforting that the fossil evidence
does back up my beliefs. Woese's belief that thermophily is a
plesiomorphic characteristic that offers a window on life's origins
should also be looked at with extreme skepticism.
>Thomas Schlemmermeyer asked for examples of windows to the past.
>Windows to the past are more often illusions than reality for a simple
>reason. Primitive groups do not generally survive, almost by
>They are replaced by more advanced groups. Representatives of primitive
>groups survive in two ways.
>1. As relicts in isolated geographic locations. The NZ tuatara
>one such example.
>2. As modern representatives of old groups. Monotremes in Australia and
>chamaeleons in Africa are good examples. Both are very successful, but
>Members of the first group may indeed be windows to the past. The
>group should be treated with caution because they are essentially
>taxa with a few more plesiomorphic characters, but nevertheless highly
>modified. Even members of the first group should be treated as windows
>the past on the understanding that they are likely to be hotel windows
>ocean views. You might be standing on the toilet looking through a
>the paint to see the sea....
>Department of Anatomy and Physiology
>RMIT - Bundoora
>PO Box 71
>Bundoora Victoria 3083
>email gjw at rmit.edu.au
>Phone 61 3 9468 2589
>Fax 61 3 9467 8589
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