The neutral theory of molecular evolution

By the early 1960s amino acid sequences of hemoglobins and cytochrome c for many mammals had been determined. When the sequences were compared, investigators began to notice that the number of amino acid differences between different pairs of mammals seemed to be roughly proportional to the time since they had diverged from one another, as inferred from the fossil record. Zuckerkandl and Pauling [8] proposed the molecular clock hypothesis to explain these results. Specifically, they proposed that there was a constant rate of amino acid substitution over time. Sarich and Wilson [6, 7] used the molecular clock hypothesis to propose that humans and apes diverged approximately 5 million years ago. While that