In the general biology labs that I teach, the students map out which portions of their tongues can taste sweet, sour, salty, and bitter chemicals. Of course, they hate the bitter quinine.
The ability to taste bitter compounds, and to dislike them, is of immense importance to our survival today as it has been throughout animal evolution. Most bitter compounds are potentially toxic, and if we taste something bitter, we may need to stop eating it so quickly that disgust, rather than rational decision, is necessary.
One student, however, was unable to taste the quinine. I never found out if he could taste any other bitter compounds. This is not a good thing for him. He has to be extremely careful about what he consumes.
According to a genetics website at the University of Utah, “Humans have about 30 genes that code for bitter taste receptors. Each receptor can interact with several compounds, allowing people to taste a wide variety of bitter substances.” This is because a wide variety of different molecules can be toxic. Many medicines are toxic in large quantities, and taste bitter even in small quantities; and these medicines are not chemically similar to one another. The ability of the human tongue to detect “bitter” is actually thirty different abilities. In this way the human brain has a single response—“This is bitter, don’t eat it”—to a great variety of potential threats.
Next time you taste something bitter, think about this and feel a little gratitude to your nervous system for protecting you.