In recent years, humans have gained the ability to navigate with satellite-based GPS systems. But some animals possess internal GPS systems, probably for millennia. The amazing explanation for this feature—which scientists are uncovering—is that certain species are able to read small variations in the intensity of Earth’s magnetic field and use that to guide them to their destination.
A recent article1 in the Proceedings of the National Academy of Sciences (PNAS) reports that researchers were able to “reproducibly detect magnetic cells” firmly coupled to the cell membrane in the trout olfactory epithelium (the tissue in the nasal cavity linked to smell).2 This article states that trout’s magnetic cells “clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field.”
Over 50 years of scientific study of this phenomenon have revealed that it is made possible because magnetite3 (a highly magnetic mineral) occurs naturally in the cells of many organisms—including the human brain.4
Pigeons are similarly endowed with magnetoreceptors. An article featured in the May 25, 2012 issue of Science describes research which suggests this is due to the design of the pigeon brainstem:5
Neuronal responses in the pigeon’s brainstem...show how single cells encode magnetic field direction, intensity, and polarity—qualities that are necessary to derive an internal model representing directional heading and geosurface location.
And yet another recent paper in
Cutting through the technical jargon: scientists are piecing together how salmon know to travel hundreds of miles to the spawning ground of their birth, how homing pigeons know how to find home, how sea turtles know the roundtrip route from Florida to Africa, and how a variety of animals have an intuitive directional sense that has defied explanation for centuries.
This research is revealing that many animals have natural magnetoreceptors that read and interpret the Earth’s magnetic field.
The Planet’s Magnetism
Earth possesses a natural magnetic field that points roughly north-south. In the presence of a strong magnetic field, a material such as magnetite is drawn to align with the field. A freely moving compass needle will thus point north and help explorers find their way. Compasses have been used as navigation tools for centuries, but their use is limited. Although there are variations in the magnetic field—it is weaker the farther one is from the magnetic north pole and the higher one is from Earth’s surface—a compass still points strictly north-south; it provides no indication of east-west longitude.
The Earth’s magnetic field is pervasive, but it is not strong—otherwise our many magnetic instruments (including car door locks) might not work. Magnetic fields are measured in Tessla (T), Gauss (G), or microTessla (µT); 1 G = 0.0001T, 1 µT = 0.000001T. The intensity at the Earth’s surface is about 30–60 µT. By contrast, a small bar magnet measures about 10,000 µT, and an MRI machine produces fields above 1,000,000 µT.7 This is why a small bar magnet will attract a compass needle away from magnetic north, and why patients are told to remove all metal objects before undergoing MRI scans.
Moreover, just as two magnetic objects interact to attract or repel one another, a magnetic object affects a magnetic field: the object distorts the field and causes local variations in direction and/or intensity. A steel pocketknife causes a small distortion in the Earth’s magnetic field, but a mountain of iron ore causes a larger distortion. Hence the field intensity varies across the surface of the planet, both in general8 and in localized areas. (These variations can be scrutinized at the National Geophysical Data Center website, which has an online program to calculate seven field parameters for the magnetic field at a particular time and location.9)
In summary, the Earth’s magnetic field is small, and the subtle variations in the field are even smaller. Nevertheless, certain animals are able to read the field parameters precisely and use this information for migratory purposes. The Science article on pigeons’ neuronal responses suggests:10
MR [magnetic response cells] encode a geomagnetic vector that could be used…to computationally derive the bird’s position and directional heading. The geomagnetic vector elevation component could provide the bird’s latitude, the vector azimuth component could be used as a magnetic compass to provide heading direction, and the vector magnitude could provide spatial position cues through local variations in intensity relative to a learned model of geomagnetic space.
This describes a very complex “computer” program using more than three variables! But note a critical element: the bird (or fish or turtle or other animal) often has a magnetic “map” (called the “learned model”) programmed into its brain, and follows this map to its destination.
In the Current Biology article discussing sea turtles, the authors “subjected hatchlings to [magnetic] fields replicating those found at two locations, both of which lie along the migratory route but on opposite sides of the Atlantic.” Researchers found that the turtles exposed to a field like the one near Puerto Rico swam approximately northeast, while those exposed to a field near the Cape Verde Islands swam approximately southwest.11
These results add to the growing evidence that specific regional magnetic fields elicit orientation responses that help young loggerheads [turtles]…advance along the migratory route. The hatchlings we tested had never been in the ocean, demonstrating that turtles do not need migratory experience in order to recognize and respond to fields that exist along their oceanic pathway.
In other words, this research suggests these animals are born with a preprogrammed internal magnetic “map”—it is not a learned response. Moreover, some of the migration routes are quite complex. For example, the pied flycatchers’ route takes them from central Europe southwest to Iberia, then southeast to travel around the Alps, the Mediterranean Sea and the central Sahara.”12
The question then is, where did these inborn, internal magnetic maps come from? Did they evolve or are they the result of design? We’ll explore this question next week.
Dr. Hugh Henry, PhD
Dr. Hugh Henry received his PhD in Physics from the University of Virginia in 1971, retired after 26 years at Varian Medical Systems, and currently serves as Lecturer in physics at Northern Kentucky University in Highland Heights, KY.