Neutral changes during divergent evolution of hemoglobins.

A comparison of the mRNAs for rabbit and human beta-hemoglobins shows that synonymous changes in codons have accumulated three times as rapidly as nucleotide replacements that produced changes in amino acids. This agrees with predictions based on the so-called 'neutral theory'. In addition, seven codon changes that appear to be single-base changes (according to 'maximum parsimony') are actually two-base changes. This indicates that the construction of "primordial sequences" is of limited signficance when based on inferences that assume minimum base changes for amino acid replacements.