 AVT (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Arg-Gly-NH2), which occurs in the lamprey, represents the ancestral form in the phylogeny of the vertebrate neurohypophysial hormones.Gene duplication and point mutation have produced two distinct lineages, one involved in reproduction (oxytocin-like peptides) and the other in osmoregulation (vasopressin-like peptides).These hormones have remained highly conserved throughout evolution.