Human Eye May Have Magnetic '6th Sense' Light-sensitive human protein acts as 'compass' when present in flies By Rob Quinn, Newser Staff Posted Jun 22, 2011 9:50 AM CDT 10 comments Comments The eye may have doubled up as a navigational tool in humanity's past, researchers say. (Shutterstock) (Newser) – The human eye may be an even more amazing thing than we realize, capable of acting as a compass by sensing the Earth's magnetic field, new research suggests. Cryptochrome, a protein believed to give animals like migratory birds and sea turtles their ability to navigate, is present in the human eye. When scientists added human cryptochrome to flies that had their own version of the protein genetically engineered out, the flies' ability to respond to a magnetic field was restored, reports the BBC. Similar experiments with monarch butterflies had the same result. More research is planned, but some scientists say human magnetosensing, if it exists, will be tough to detect because—as with the circadian rhythms cryptochrome is also believed to play a role in—people likely react to cryptochrome without being aware that they are doing so. "I would be very surprised if we don't have this sense; it's used in a variety of other animals," the lead researcher says. "I think that the issue is to figure out how we use it."