Natural selection can drive the evolution of similar traits through convergent evolution. Peptides identical to certain vertebrate hormones are present as toxins in the venoms of species of ants and wasps (hymenopterans) and the skin secretions of frogs. The genes encoding the hymenopteran and frog peptide toxins do not share common ancestry with those of the vertebrate hormones but instead independently evolved, sometimes multiple times, from other peptide toxin genes. These peptides serve a defensive function against vertebrate predators and their resemblance to vertebrate hormones was driven by selection for efficacy at the predators’ receptors. These studies highlight how with a suitable genetic substrate and shared environmental pressure, natural selection can result in repeated convergent evolution of identical peptides even across distantly related species.