Our senses can be divided into three different categories: contact
senses, distance senses, and internal senses. Contact senses include
taste, our sense of pressure, and our sense of heat and cold. Distance
senses include vision, hearing, and smell. Internal senses include
our sense of balance and muscle stretch. Collectively these senses
allow us to generate an internal description of the world.
Many life forms have no distance senses, relying on contact and
internal senses. Plants, for example, cannot see, hear, or smell,
though some plants can sense pressure and vibration. Even some simple
members of the animal kingdom, such as the amoeba, have no distance
senses, relying on physical contact for information about food and
predators. The psychological world of these creatures is limited and
Our distance senses provide a more comprehensive picture of the world
around us. We can detect predators, and escape or avoid them; we can
locate prey, and try to capture it; we can find resources like water,
shelter, and tools, and take advantage of them, all by using our distance
Distance senses work in harmony to achieve these ends. We may hear
a babbling brook long before we can see it, but we realize that water
is nearby and know which direction to take. Once we get in the general
vicinity of the brook, we see it and walk confidently to the water's
edge for a welcome drink. We may smell a predator, but not know precisely
where it is lurking, then listen and watch for more signs of the stalker.
All this knowledge comes to us without direct physical contact, the
hallmark of distance senses.
Creatures that enjoy distance senses have a tremendous advantage
over those that cannot sense at a distance. If we had to rely on physical
contact to alert us to a predator, it would probably be too late!