Evolution and Secondary Pathways

The occurrence of secondary metabolism is a feature common to all living organisms, but restricted to certain taxa. Intermediary metabolism and its products are reasonably well known, but our knowledge of secondary pathways and metabolites is still very limited. Starting from given precursors from intermediary metabolism, in secondary metabolism the evolution of biochemical pathways can proceed in all directions provided that the metabolites are toxic to the producing organism, at least not at the time of their appearance. The main selection principle during the evolution of organisms which can afford the "luxury" of a biochemical playground cannot be fast growth and short generation times. A continuous evolution of biochemical pathways in secondary metabolism must occasionally lead to compounds which offer an advantage to the producing organism. The playground of secondary metabolism is probably a very early relic of biochemical evolution.