  Part 1 of the study intends to show that the universal trend of amino acid
gain and loss discovered by Jordan et al. (2005) can be accounted for by the
spontaneity of DNA typical damages. These damages lead to replacements of
guanine and cytosine by thymine. Part 2 proposes a hypothesis of the evolution
of the genetic code, the leading mechanism of which is the nucleotide
spontaneous damage. The hypothesis accounts for the universal trend of amino
acid gain and loss, stability of the genetic code towards point mutations, the
presence of code dialects, and the symmetry of the genetic code table.
