This from 'Evolution', Strickberger
concerning problems with the RNA world concept.

"We can calculate that 90% fidelity of replication
will conserve a molecule no longer than 12
nucleotides,... whereas 95% fidelity of replication
will conserve a molecule about twice as long.
Similarly, superiority of survival influences
length: the greater its relative superiority over
other molecules, the longer the sequence of 
nucleotides that can be maintained for some given
fidelity of replication. But fidelity... has an 
essential requirement ... that an RNA molecule
be long enough to act as a replicase enzyme....
Joyce and Orgel suggest that the minimun length
for RNA catalytic activity is possibly a 
triple stem-loop containing 40-60 nucleotides.
.... (less than exact fidelity leads to mutation)
.... High mutation rates might seem an advantage
in a rapidly evolving world, (but) they would cause
increasingly inefficient enzymes with each
mutational generation..." 
*  *   *
But IF the RNA was solely selected as that
which survives the heat cycle, then at the end
of the day you would have RNA with 100% fidelity
(fidelity to its purpose of surviving that environment)

Thus if you look at the problem of fidelity through
the eyes of one who wants to get RNA TO a certain
advanced place in the future - it presents tough and 
almost unsurmountable problems

But if you look at RNA as that that best survives
that environment, and also has the ability to
produce variants that might survive even better,
then it has 100% fidelity of surviving its environment.

I suggest surviving its environment is the cause for life
NOT a chemistry system that evolves to what we want
billions of years down the line.
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 * RgateImp.MoonDog.BBS at 5/6/04 10:46:47 PM