TomHendricks474  wrote or quoted:

> > RNA seems /particularly/ unlikely as the first replicator - since
> > its replication is blocked by isomeric impurities in its bases -
> > as described by J. Maynard Smith on p. 73 of "The Major Transitions
> > in Evolution".
> 
> I'd like to know more about this - a web page anywhere
> on this that you know of?

The following study describes the problem:

``The case for an ancestral genetic system involving simple analogues of 
  the nucleotides.

  Joyce GF, Schwartz AW, Miller SL, Orgel LE.

  The idea that the first living systems on earth were based on 
  self-replicating RNA molecules has recently become popular as a result 
  of the discovery of ribozymes. However, there are several major 
  problems associated with the prebiotic synthesis of ribonucleotides. In 
  addition, there is the newly recognized problem of enantiomeric 
  cross-inhibition, whereby template-directed polymerization involving 
  one enantiomer of RNA is inhibited strongly by the presence of the 
  other enantiomer. Here we propose that RNA was preceded in the 
  evolution of life by a polymer constructed from flexible, acyclic, 
  probably prochiral nucleotide analogues that were synthesized readily 
  on the primitive earth. Several potentially prebiotic nucleotide 
  analogues are considered in this context, and some of the consequences 
  of this proposal are discussed.''

 - http://calorierestriction.org/pmid/?n=2440020

Incidentally, it appears that PNA is similarly afficted:

``Enantiomeric cross-inhibition in the synthesis of oligonucleotides on a 
  nonchiral template.''

 - http://calorierestriction.org/pmid/?n=11539924
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