Evolutionary rate of cistrons and DNA divergence

The ratio of DNA divergence to cistron divergence was estimated for various comparisons ofDrosophila and mammalian species. It was shown that a negative correlation exists between this ratio and the length of one generation. It was proposed that the majority of the amino acid substitutions in evolution are the result of random fixation of nearly neutral mutations for which selection intensity fluctuates considerably but the average selection coefficient is very slightly negative. On the other hand, the evolutionary rate of DNA divergence is negatively correlated with the generation time if the majority of mutations are completely neutral and if mutation rate at the nucleotide level is mildly dependent on the generation time.