The genetic code did not originate from an mRNA codifying polyglycine because the proto-mRNAs already codified for an amino acid number greater than one.
I reply to Bernhart and Patrick (2014) that claim that the first amino acid to be codified in the genetic code was glycine, and that from mRNAs codifying for polyglycine originated all other codons of the genetic code. Indeed, given that the origin of protein synthesis should have preceded the one of the genetic code, then proto-mRNAs codifying for polimeric catalysts of the world in which originated the protein synthesis, should have been the more direct ancestors of mRNAs that originated in the world in which evolved the true genetic code. Therefore, it is clear that there would have been at least a partial evolutionary continuity between these proto-mRNAs and mRNAs. This evolutionary continuity has as logical consequence that cannot have existed of mRNAs codifying for only an amino acid because these mRNAs would descend from proto-mRNAs that already codified for more than one amino acid. Therefore, these mRNAs would not have reshaped their codifying capability to a single amino acid, without loss in the meaning of their coding, and this could not have occurred being counter selected. I also reply to other imprecisions made by Bernhart and Patrick (2014).
['Di Giulio|Massimo|M|']
D000596:Amino Acids D019143:Evolution, Molecular D005815:Genetic Code D005998:Glycine
Polyglycine Proto-mRNAs Genetic code origin Peptidated-RNAs