In the previous 500 million years, the outcomes are totally dependable with the claim that nucleotide substitutions have been neutral. Two types of neutral nucleotide sequences such as synonymous substitutions and non-synonymous substitutions are mapped out. Both the mutations are predictable to occur at the same rate.
Synonymous substitutions do not change the amino acid sequence of a protein and usually have no phenotypic effect and so not subjected to natural selection and are estimated to mount up freely. But, in case of non-synonymous substitutions the amino sequences change and possibly have a broad range of influence on phenotype and hence, subjected to natural selection.
A greatly inferior slope for non-synonymous mutations is depicted than for the synonymous mutations, which mean the rate of evolution at non-synonymous site is lower, because non-synonymous substitutions will be least harmful and chosen besides, decreasing the frequency, whereas few will be almost neutral. So, non-synonymous substitutions will be likely to accumulate much more slowly and be situated at a lower rate than the synonymous substitution. This type of common tendency would not vary from gene to gene. Hence, the effect would be expected to appear for most genes.