In the beginning, living systems were relatively simple and depended upon only a small number of macromolecules for metabolic activity and continued existence. Evolutionary progress entailed the acquisi-tion of new macromolecules and metabolic processes, eventually resulting in the great variety and biochemical complexity of the life forms that exist today. Early biological evolution required the creation of new metabolic machinery en-coded innew deoxyribonucleic acid (DNA). However, much subsequent evolutionary change has depended primarily upon the modification and elaboration of preexisting components, particularly the DNA (1, 2), as indeed the term evolution