Molecular Evolution Activities



Online Document

Motoo Kimura, "Evolutionary Rate at the Molecular Level," Nature 217 (1968), 624-626.
[Summary] [PDF 219K]

Kimura begins by stating that recent studies have shown that many mammalian proteins seem to evolve at a steady rate, which he then averages to get a figure of approximately one substitution per 28 x 10(6) years for a 100 amino acid polypeptide. Based on this figure, he concludes that in the evolutionary history of mammals, there has been a nucleotide substitution in "the population" roughly once every two years. He then argues that this evolutionary rate is "in sharp contrast" to Haldane's estimate of one substitution roughly every 300 generations, which was calculated using a cost of selection argument. Kimura claims that mammals could not tolerate the rapid nucleotide substitution that he calculates if there is a cost (or "substitutional load") for each one. Therefore, he argues that the high rate of molecular evolution he calculated can only be reconciled with the limits set by the substitutional load by assuming that most mutations produced by nucleotide replacement are neutral. In his conclusion, Kimura points out that if his theory is right, biologists will have to pay more attention to the role of random genetic drift in evolution than had been fashionable in the past decade. (jda)


This page was written by Michael Dietrich and Jay Aronson. It was last updated on May 15, 2004.