The distinction between primary and secondary metabolites is not always easily made. At the biosynthetic level, primary and secondary metabolites share many of the same intermediates and are derived from the same core metabolic pathways. Secondary metabolites generally, but not always, occur in relatively low quantities and their production may be widespread or restricted to particular families, genera, or even species. They were known, however, to have significant economic and medicinal value and were thus of more than a passing interest to natural products chemists. In recent years, however, it has become increasingly evident that many natural products do have significant ecological functions, such as protection against microbial or insect attack.