  We apply Markov chain lumping techniques to aggregate codons from an
empirical substitution matrix. The standard genetic code as well as higher
order amino acid substitution groups are identified. Since the aggregates are
derived from first principles they do not rely on system dependent assumptions
made beforehand, e.g. regarding criteria on what should constitute an amino
acid group. We therefore argue that the acquired aggregations more accurately
capture the multi-level structure of the substitution dynamics than alternative
techniques.
