A Sixth Sense?
Do humans and animals sometimes display a sixth sense? If so, how does that sixth sense operate?
People and many animals traditionally have been recognized as having been endowed with five senses. These--sight, hearing, touch, taste and smell--provide the stimuli that allow most animals to sense their environments and to operate effectively within it.
One can argue that animal senses tend to come in pairs, according to the mechanisms involved. Taste and smell form one pair in that both operate chemically. Molecules to be tasted or smelled are first dissolved in water within the mouth or nose, and the actual sensing by taste buds or olfactory cells is through chemical action. Of this pair, taste can be considered as a contact sense because an object to be tasted has to go into the mouth. On the other hand, smell works at a distance; we can smell a flower without contacting it.
Another pair of senses, hearing and touch, operate by mechanical forces only. Touch is the contact sense of the pair whereas hearing is the distance sense. Normal hearing is accomplished by responding to air vibrations that can emanate from distant sources. Curiously, both touch and hearing require motion. Unless there is at least a little motion between one's finger tips and a touched table, the brain does not recognize that the table is being touched.
Now we come to the last pair, the pair that uses electromagnetic forces. By comparison with the taste-smell and touch-hearing pairs, one expects the electromagnetic senses to have certain characteristics. For example, one of the pair should be a contact sense, the other be a distance sense. The names of the electromagnetic senses are sight and--whoops, there is no generally recognized sixth sense! But it seems that there should be. Since sight is the distance sense, the sixth sense should be a contact sense. Also by analogy with the other sensory pairs one expects that the sixth sense operates on low-frequency electromagnetic forces, namely relatively slow-varying electric and magnetic fields.
Does the sixth sense really exist? Possible magnetic field sensory organs have been found in homing pigeons and in Monarch butterflies. Both have tiny magnetic field-sensing materials in their bodies that could be used for navigation. Millions of tiny compass-like magnetite crystals occur in a pod next to the pigeon's skull; in the butterfly the magnetite is distributed in the wings. Now that magnetite has been found in these animals, it seems likely that future research will discover its existence in others.
With regard to an animal's ability to sense slow-varying electric fields, the situation may be less certain. However it is known that bones do exhibit electrical characteristics. These characteristics have been found useful for speeding up the healing of broken bones. An electric current passed through the ends of a fractured bone apparently does promote rapid bone growth in the fractured region.
It might turn out that the saying "I feel it in my bones" is not so far off the mark when it comes to sensing electric fields. But the future might cause us to alter another saying: instead of describing an animal that seems to perceive unseen or unknown things as having a "sixth sense", someday we might say that they have a "seventh sense," perhaps even an "eighth sense".
