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From the standpoint of the neutral theory, the clocklike progression of molecular evolution can be explained by assuming that the rate of production of neutral mutations per year is nearly constant among related organisms for a given molecule over time.   \end{quotation}    The precise fidelity claim of clocklike progression  ofthe  molecular clock evolution  was quickly brought into question examined  by a series of empirical studies that showed that the variance of the molecular clock was greater than would be expected from Poisson error alone \cite{} \cite{LangleyFitch1974}     
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