Birds can "see" magnetic fields to navigate by having eyes with low levels of toxic superoxide in combination with the cryptochrome photo protein molecule. Scientists in Germany and the University of Illinois have found a chemical reaction in which the cytochrome photoreceptor can be influenced by orientation with respect the magnetic field of the earth through "Zeeman and hyperfine" interactions to give birds the magnetic compass sense.
Crytochrome is also present in the human eye but our superoxides are even lower, enhancing longevity, whereas in birds, evolution has favored a bit of cellular damage in return for navigational benefits of magnetic vision, according to biophysicist Klaus Schulten of the Urbana Champaign campus. (Reported in Biophysical Journal/Science Direct)
POSTER COMMENT: I wonder if there's the odd human who has a magnetic orientation sense and what eye damage, if any has been encountered.
Click for Full Text!