The Sense of Taste

Our senses of taste and smell provide a window on the chemical world around us. We taste food in our mouth with the chemical receptors that dot our tongue, and we smell molecules suspended in the air with chemical receptors deep in our nasal passages. Without these two senses, our world would seem emptier and we would know less about it. Indeed, our senses of taste and smell not only add pleasure to our lives, they protect us from danger.

It is clear that our senses of taste and smell serve several purposes. But these two senses are far less important than some of our other senses. The loss of our ability to taste or to smell would not have the same negative impact on our lives that sudden deafness, or even more so, blindness, would have. For many types of animals, however, the loss of their sense of smell or taste could be life threatening.

Many small mammals, such as mice, voles, and weasels, are as dependent on their sense of smell as we are on our sense of sight. These animals live close to the ground, and many are nocturnal. In these conditions smell provides far more information than vision ever could.

Fish, too, rely heavily on their ability to sense their chemical environment. These creatures have receptor cells scattered over the surface of their bodies. (Imagine having taste buds on your arms and legs, torso, and the top of your head, and thus being able to taste not only the wind as it blows by but also the surface of the chair you're sitting in!) The brain anatomy of most fish suggests the importance of being able to sense chemical information in an aquatic environment: The area of the brain that receives information from these receptor cells is typically larger than all of the brain's other sensory centers combined. These examples make it clear that the importance of a particular sense and its degree of sensitivity have evolved in a species at the same time that other characteristics were evolving. Life in dark burrows, for example, has minimized the snake's need for legs and maximized its need to taste the air with its forked tongue. Humans, in contrast, evolved from primates that spent most of their time in trees. High above the forest floor, leaping from limb to limb, our ancestors had far less use for smell and taste than for keen vision.

Investigate the senses involved with taste in this NOVA classroom activity.

• The narrator says that "sweet taste makes sure that the baby will drink the mother's milk." Do you think that 1) the milk is sweet because the baby likes the taste of sweetness; 2) the baby develops a taste for sweetness because the mother's milk is sweet; or 3) the two traits developed side by side? Give your reasons for your answer.
• Why doesn't food taste very good when you have a bad cold?