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\section{Introduction}   Zuckerkandel and Pauling were arguably the first to suggest the existence of a ``molecular evolutionary clock'' such clock'', based on evidence  that the rate of evolutionary change of molecular sequences appears appeared  to be very similar per unit time across diverse lineages \cite{zuckerkandl1965}. Allan Wilson was a pioneer of the application of the molecular clock and one of the first examples of a molecular phylogeny challenging palaeontological evidence came from Wilson and Sarich's paper entitled ``A molecular time scale for human evolution'' \cite{WilsonSarich1969}, in which they estimated an age of the common ancestor of humans and chimpanzees of 4-5Myr, far more recent than the accepted figure of 20-30 Mya that had been proposed by palaeontologists.