Scientists at the University of Tsukuba analyzed the hagfish genome and found an unexpectedly large set of vomeronasal-type receptor genes. Published in iScience, the discovery suggests these chemosensory receptors may have arisen earlier in vertebrate evolution than previously believed. Researchers propose the expansion is linked to hagfish adapting to dim, deep-sea environments where smell guides scavenging and mating behavior.
Slimy Hagfish May Have Helped Shape the Evolution of Our Sense of Smell
Lead image: Freshwater and Marine Image Bank
Smell is central to daily life and played a key role in vertebrate evolution, helping early mammalian ancestors locate food, communicate and evade predators. New genomic evidence suggests that some of the chemosensory building blocks of that ability may go back even further than previously thought — to ancient, slime-producing hagfish of the deep sea.
Hagfish are gelatinous, eel-like fishes that evolved more than 300 million years ago and belong to one of only two living lineages of jawless vertebrates. Although they retain many primitive features, hagfish possess a surprisingly sophisticated olfactory system that helps them find carrion, forage and locate mates in dim, deep-water environments.
Genome Study Reveals Unexpected Receptors
Researchers at the University of Tsukuba in Japan analyzed the hagfish genome to trace the diversification of genes involved in chemical sensing. They specifically searched for families of genes that encode olfactory receptors and vomeronasal-type receptors — the latter often associated with detecting pheromones and other social or environmental chemical cues.
The team discovered a "surprisingly large set" of genes related to a class of vomeronasal receptors, a finding reported in the journal iScience. This challenges the long-standing view that vomeronasal-type receptors originated only in jawed vertebrates and suggests these receptor families may have appeared earlier in vertebrate history than scientists assumed.
Why It Matters
These genetic signals imply that adaptation to low-light, deep-sea habitats — where smell is often more useful than vision — could have driven early expansion of chemical-sensing genes. By highlighting the unexpectedly complex chemosensory repertoire of hagfish, the study positions these overlooked animals as valuable models for understanding the origins and evolution of vertebrate senses.
"This finding calls attention to the importance of the hagfish, which has often been overlooked, yet holds significant potential to illuminate critical aspects of early vertebrate evolution," the authors wrote.
So the next time you savor the smell of freshly baked pie or a flower-filled meadow, consider that the deep-sea ancestors of vertebrates — slimy, scavenging hagfish — may have helped set the stage for how animals detect and interpret odors today.
