Magnetoreception mechanism in animals

Partly settled. Some of it is understood, some is still argued about.

Wolfgang Wiltschko's 1972 experiments first demonstrated that European robins use an internal magnetic compass for orientation, launching decades of research into how any animal could sense a magnetic field as weak as Earth's. The leading hypothesis, developed since the 1970s-2000s, proposes that light striking the protein cryptochrome in the retina creates pairs of chemically reactive 'radical' electrons whose quantum spin states are subtly influenced by the ambient magnetic field, altering the protein's chemistry in a way the animal could perceive. Laboratory studies through the early-to-mid 2020s have shown cryptochrome from migratory birds is magnetically sensitive in vitro and behavioral experiments support radical-pair involvement, but a complete, undisputed chain from magnetic field to cryptochrome chemistry to nerve signal to behavior in a living animal has not yet been fully demonstrated.

A songbird crossing an ocean at night may be literally seeing Earth's magnetic field thanks to quantum spin physics happening inside a protein in its eye.

Explanations that circulated

• That magnetoreception has been conclusively proven to work via the radical-pair quantum mechanism in cryptochrome — this remains the leading and best-supported hypothesis (with strong in-vitro and behavioral evidence through the early 2020s), but a magnetically sensitive radical-pair reaction has not yet been demonstrated to directly drive animal behavior in vivo, and a competing magnetite-based mechanism may also contribute in some species

References

• The radical-pair mechanism of magnetoreception, P. J. Hore, Henrik Mouritsen, Annual Review of Biophysics, 2016