What are antibiotics? Archaic functions for modern activities.

Secondary metabolites are proposed to have played important roles in the evolution of the reactions of living forms on earth, in effecting and modulating reactions during biochemical evolution by chemical and structural interaction with 'receptor' sites in primitive macromolecular templates. For example, in the evolution of the translation system, as the polymerizing reactions became more complex and proteins became involved, the low molecular-weight effectors were functionally replaced by polypeptides, but retained their ability to interact with receptor sites in nucleic acids and proteins. Many of these low molecular-weight effectors now play a different role, that of antagonists, by interacting with the original receptor sites in macromolecular structures; this explains their contemporary activity as antibiotics.