Introduction: Genetic information contained in mRNA is in the form of codons, sequences of three nucleotides, which are translated into amino acids which then combine to form proteins. At certain sites in a protein's structure, amino acid composition is not critical. Yet certain amino acids occur at such sites up to six times more often than other amino acids. In the 1960's, molecular biologists sought to determine if amino acid composition was a reflection of the genetic code or if certain amino acids were naturally selected as optimal.
Question: Are frequencies of particular amino acids simply a consequence of random permutations of the genetic code or instead a product of natural selection?
Supplement to 'The Genetic Code': https://cnx.org/contents/jVCgr5SL@15.43:aXYynRWE@10/15-1-The-Genetic-Code