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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.
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