First, thanks for introducing to me about codon. But I think it is not exactly relevant here. We are not talking about genetic diversity (a.k.a genepool) but DNA length (number of base pairs). OP implied that since human DNA length is shorter than ancestor, we devolved, which is rubbish. DNA not only contains useful information, but lot of it is junk/non-functional (or function not understood). Further, lot of genetic code is for "switching/timing" rather than making any protein (they switch other DNA on/off at specific timing). So, just because an organism has less number of base-pair (or DNA length), it doesn't mean "less evolved or devolved". My point is, there is no such thing as "devolution". If our ancestors had small tails and we don't but our successor species has even longer tails (due to say, in response to a specific natural pressure), it doesn't mean our successor species "devolved", it still means they evolved. The point of evolution is survival and until that (species survival) happens, by whatever response or change in the appearance/genetic code etc etc, it is still considered as evolution.