Migratory animals such as birds, turtles, and fish navigate using Earth's magnetic field, a sense known as magnetoreception, but its evolutionary origins remain unresolved.
Recent studies indicate that the magnetic navigation systems in complex animals likely arose separately from those in bacteria, rather than through direct genetic inheritance.
Bacteria inherited magnetite biomineralisation from ancient archaea, which formed iron oxide crystals to manage iron toxicity in early anoxic oceans. Some bacteria later arranged these crystals into chains that function as microscopic compasses.
A common magnetosome gene cluster underpins this bacterial ability, but searches have not found the same genetic signature in animals that display magnetoreception.
The only confirmed link between bacteria and eukaryotes occurs in single-celled protists, which acquire magnetoreception by ingesting or hosting magnetotactic bacteria.
Research on chitons, marine molluscs that form magnetite teeth for grazing, shows they use a unique protein and an extracellular process unlike the intracellular vesicle method of bacteria.
Scientists propose that animals may have independently evolved magnetite production by modifying existing iron-handling systems, later connecting it to the nervous system for navigation.
Despite progress, no magnetic receptor cell has been definitively identified in any animal, leaving the precise mechanism and evolutionary pathway open to further investigation.
New clues into how animals evolved an internal compass to navigate Earth
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