Metabolic and membrane-altering toxins, molecular differentiation factors, and pheromones in the evolution and operation of endocrine-signalling systems.

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