METABOLIC AND MEMBRANE-ALTERING TOXINS, MOLECULAR DIFFERENTIATION FACTORS, AND PHEROMONES IN THE EVOLUTION AND OPERATION OF ENDOCRINE-SIGNALING SYSTEMS

The endocrine systems of vertebrates and higher invertebrates may have evolved functionally from as far back on the evolutionary scale as ba cteria and early multicellular organisms and their biological communit ies, which have been shown to produce a variety of cyclic nucleotides, peptides, fatty acids, prostaglandins and sterols with endocrine-alte ring effects in primitive as well as more highly evolved species.