In a way that is similar to how an everyday compass reacts to the earths magnetic field, scientists have discovered that a protein present in human eyes, may in fact behave in a similar fashion.
... This magneto-receptive protein called cryptochrome, is present – in one of two forms – in every animal on planet Earth. What Dr.Reppert of the University of Massachusetts Medical School has shown is that if this protein is removed from the eyes of a fly, it loses it’s ability to respond to a magnetic field.
Subsequently, if the human version of this protein is then made available in the flies’ eye, through genetic engineering, this ability returns.
This work seems to imply that humans may in fact have a built in ability to respond to magnetic field lines in some way.
Earlier work done on this was carried out by a Dr Robin Baker of the University of Manchester in the 1980s. Over hundreds of experiments involving thousands of volunteers, he claimed to find subtle evidence that humans could indirectly sense magnetic fields.
Perhaps these scientists are onto something? It would certainly make sense that through our evolution as a species, we once developed an ability to navigate using an in-built compass.