it suggests fewer amino acid changes are being fixed in the population than we would expect by chance compared to the fixation rate of silent mutations it suggests fewer silent mutations are being fixed in the population than we would expect by chance compared to the fixation rate of amino acid changes it suggests more amino acid changes are being fixed in the population than we would expect by chance compared to the fixation rate of silent mutations it suggests more gene duplications are being fixed in the population than we would expect by chance compared to the fixation rate of deleterious amino acid mutations