deletions | additions       diff --git a/introduction.tex b/introduction.tex  index 8a61d11..3a43cd5 100644  --- a/introduction.tex  +++ b/introduction.tex 
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The fundamental conclusion of even the most rudimentary analysis is that amino acid sequence differences correlate well with morphological and paleontological considerations.  \end{quotation}  Despite this they went on to show evidence that rates of nucleotide substitution are not constant across vertebrates \cite{LangleyFitch1974}.  Evidence for or against  the existence of a molecular clock (sometimes known as the `rate-constancy hypothesis') played provided  a key role in support of the neutral theory of evolution and thus formed one of the battlegrounds between battleground on which  neutralist and selectionist views of molecular evolution were contested  \cite{Kimura1987}. Kimura \cite{Kimura1987} put it thus: 
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