Migratory birds don’t break out the sextants on their migrations north and south because they can literally see the Earth’s magnetic field. It’s like an extra layer of data in their optic system that adds to what we normally think of as visual information. New research suggests that they may not be alone: wolves, bears, foxes, badgers, and orangutans might have this superpower as well. German scientists have found that these species have the same photoreceptor in their retinas that gives birds this specific ability. Domesticated dogs also have it (cats don’t).
Just because the receptor is present, however, doesn’t mean that it’s being used. Humans actually carry the photoreceptor, too, although there isn’t much evidence to suggest that we’re able to use it to tell which way is north. It’s possible that humans once had the ability to see the magnetic field, but lost it as we became reliant on compasses and maps. Nurture can defeat nature over an adequate number of generations.
We do know that sight is more complicated than seeing; that, for instance, a blind person can learn to visualize the world again by using echolocation. The fascinating thing about this is not that it’s an alternative to sight, but that echolocators use the same parts of their brain to navigate as people who can see. It makes some sense, therefore, that some species that don’t have the receptor can tell their north from south. These include some rodents and bats. The blind mole rat, for example, probably uses magnetite particles within its cells as an internal compass in the dark subterranean passages it calls home.
Given how useful compasses are, it should really be no surprise that animals have evolved more than one way to carry them within ourselves. And yet we’re amazed. We’re bowled over that what we consider to be an incredible feat of human engineering may have existed inside of us, all along.