Geomagnetic eyes in birds

Geomagnetic eyes in birds                                                                                                                                                                                                                                                      Superoxide is a toxic free radical which help birds see the earth’s magnetic field with the help of which birds migrate from one place to another. Birds eyes have a photoreceptor called cryptochrome that acts as a biochemical compass. The compass has a reaction partner called the superoxide. It is highly toxic and present in very low quantities and is required for the compass to work effectively. It is only because of the its toxicity that human eyes do not have a geomagnetic sense even though they have cryptochrome. During the course of evolution its toxic partner was lost.