The great magnetic mystery…an exciting new development

Lots of animals use the earth’s magnetic field to help them find their way around. They range from newts, lobsters and ants to birds, fish and marine turtles. So it looks as if magnetic navigation has a very ancient evolutionary lineage.

But we still don’t know for sure how it works.

There are two leading theories - which are not mutually exclusive.

The first is fairly simple. The idea is that animals make use of particles of magnetic minerals (typically magnetite) inside their bodies. As the animal moves through the earth’s magnetic field these particles are subjected to minute forces that twist or pull on them.

Sensory nerves connected to the particles may allow the animal to detect these forces and infer something useful about the character of the surrounding field. Some scientists think that a mechanism like this might even enable an animal to work out roughly where it is on a kind of mental map, though that is controversial.

But a very different theory has been attracting a lot of attention. The idea here is that a light-dependent subatomic process may be involved.

Certain molecules (‘cryptochromes’) react to the impact of a photon of light by briefly generating a so-called ‘radical pair’ of electrons. In theory, the behaviour of such a ‘radical pair’ could be affected by the orientation of the surrounding magnetic field. If these extremely subtle changes could somehow be amplified, they might provide the basis of a biological compass.

It’s even been suggested that migrating birds (which have cryptochrome molecules in their eyes) might ‘see’ the surrounding magnetic field superimposed on their visual field - a bit like a pilot’s head-up display.

Well, this has been the ruling theory among bird navigation researchers for some years now, but there is another intriguing possibility. It hasn’t received much attention until recently but it’s just got a very big boost.

It involves the principle of electromagnetic induction.

If an electrical conductor is moved through a magnetic field a current is induced within it (this is how dynamos work). Now an  impressively thorough piece of research strongly suggests that tiny electric currents induced in the semi-circular canals of the inner ear may well be the basis of the magnetic compass which homing pigeons (and perhaps other birds) use.

This appears to be a very significant breakthrough - and is no doubt causing a stir!