Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The original proteins did not apparently contain all of the twenty present-day aminoacids.It can be assumed that the individual aminoacids were incorporated into proteins and into the code gradually so that part of the codons for a certain aminoacid began to be translated by a new aminoacid (Ikehara et al. 2002; Cavalier-Smith 2001).In this connection, it could be quite important that aminoacids formed by common metabolic pathways from common precursors are frequently coded by similar triplets (Wong 1975).For example, the pairs of sibling aminoacids, Cys–Trp, Asn–Lys and Ile–Met, each has a common set of four triplets, which differ only in a nucleotide in a single position.The coevolutionary hypothesis of the formation of the genetic code thus assumes that the development of biochemical pathways for the synthesis of the individual aminoacids was directly connected with the development of the universal genetic code (Di Giulio & Medugno 2000).