The significance of redundancy in the genetic code

The genetic code has an inherent bias towards some amino acids because of the variable number of synonymous codons per amino acid. In proteins generally, this bias is expressed in the relative proportions of the twenty amino acids. It is suggested that even though neutral mutation may be responsible for the 'expression of this bias, the latter could be providing a positive advantage by directing mutation to introduce chemically simpler and more immutable amino acids where selective criteria have become relaxed.