 Tests of the theory using DNA sequence data consist of comparisons of the relative evolutionary rates of different kinds of sites (base pairs) within codons and take advantage of the redundancy in the genetic code. The rate of neutral evolution is estimated from levels of polymorphism or numbers of segregating sites within species or the divergence between species in silent or redundant site substitutions (e.g., Dapper &amp; Wade 2020). Silent sites are those that do not result in an amino acid change in the protein and, hence, are non-functional in the usual sense. In contrast, the rate of selective change or selective constraint is evaluated relative to the neutral rate using replacement sites, those base pair changes that result in amino acid changes. If the rate of substitution or polymorphism is lower than neutral, it is evidence of selective constraint or purifying natural selection acting to prevent change and preserve function in the face of mutational damage. If the rate of substitution is higher than neutral, then it is evidence of adaptive substitution. 