The study by Wu and Li (1984) investigates the rates of nucleotide substitution in rodents (mice and rats) compared to humans, using 11 genes from each species. They find that rodents evolve significantly faster than humans, with a ratio of 2.0 for synonymous substitutions and 1.3 for nonsynonymous substitutions. This trend is also observed in the 5' and 3' untranslated regions of five different mRNAs, with ratios of 2.6 and 3.1, respectively. The authors suggest that the higher substitution rates in rodents can be attributed to their shorter generation times, leading to higher mutation rates. They discuss the implications of these findings for molecular phylogeny and the molecular clock hypothesis, emphasizing the importance of considering generation time effects in evolutionary studies. The results support the neutralist view of molecular evolution, where mutation rates play a crucial role in shaping evolutionary rates.The study by Wu and Li (1984) investigates the rates of nucleotide substitution in rodents (mice and rats) compared to humans, using 11 genes from each species. They find that rodents evolve significantly faster than humans, with a ratio of 2.0 for synonymous substitutions and 1.3 for nonsynonymous substitutions. This trend is also observed in the 5' and 3' untranslated regions of five different mRNAs, with ratios of 2.6 and 3.1, respectively. The authors suggest that the higher substitution rates in rodents can be attributed to their shorter generation times, leading to higher mutation rates. They discuss the implications of these findings for molecular phylogeny and the molecular clock hypothesis, emphasizing the importance of considering generation time effects in evolutionary studies. The results support the neutralist view of molecular evolution, where mutation rates play a crucial role in shaping evolutionary rates.