Senses

Because animals move in the environment and must obtain food in order to survive, being able to perceive their immediate surrounds is very important. Smell, touch, hearing, and vision are all very important to vertebrates’ survival.

The sense of smell, the ability to detect small concentrations of molecules, is perhaps the oldest of all the senses. Even single-celled organisms, like Amoeba, are capable of detecting food molecules and moving toward the source. Though we typically associate smelling with airborne molecules, like cookies baking in an oven, aquatic animals are also capable of ‘smelling’. Sharks, for instance, are capable of detecting a drop of blood in water from a mile away. With this detection system, animals can gain a long-range impression of their environment.

The sense of touch is also an ancient method of perception. Touch is basically the ability to detect pressure changes. Because water will conduct vibrations over a long distance, aquatic organisms, such a fish, can ‘feel’ their environment without actually coming in contact with anything. Because air is not a good conductor of vibrations, terrestrial organisms typically must make contact with an object in order to feel it.

Hearing is really a modification of touch, as it is the ability to detect pressure changes. The difference is that the information is processed as ‘sound’. Aquatic organisms probably ‘hear’ the same way they ‘feel’. But, because air is such a poor conductor of vibrations, terrestrial organisms usually have specialized structures, such as the tympanum and ossicles, that allow them to detect strong vibrations in the air and interpret them as sound.

Vision is perhaps the last sense to evolve. Vision is basically an organism’s ability to perceive light to construct an image. Some organisms, such as planaria, are capable of detecting light intensity, but not form an image. Vision is quite useful for organisms to gain a detailed impression of their surrounding environment. As long as the light being emitted or reflected from an object can strike the photosensitive portion of the organism’s eye, then it can be seen. So, vision allows us to the smalled details of a leaf or the light of stars trillions of miles away.