Pheromones have evolved in all animal phyla, to signal sex and dominance status, and are responsible for stereotypical social and sexual behaviour among members of the same species.

[1] The VNO is present in most amphibia, reptiles and non-primate mammals but is absent in birds, adult catarrhine monkeys and apes.

They appear to be distantly related to the mammalian T2R bitter taste receptors and the rhodopsin-like GPCRs.

[8] These receptors are expressed in the basal regions of VNO, where they couple to G proteins to mediate inositol trisphosphate responses.

[9] Homologues have also been identified in fish,[10] and the ligand specificity of one such receptor has been determined: a receptor from goldfish olfactory epithelium has been reported to bind basic amino acids, which are odorants for fish.