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\section{Introduction}   Zuckerkandel and Pauling\cite{zuckerkandl1962,zuckerkandl1965}  were arguably the first to describe and apply suggest the existence of  a molecular clock to obtain an ``molecular  evolutionary time scale from clock'' such that the rate of change at the level of  molecular sequence data. appears to be very similar across diverse lineages \cite{zuckerkandl1965}.