The ways in which humans use plants, foods, and drugs cause the values of individuals and, ultimately, whole societies to shift. Eating some foods makes us happy, eating others sleepy, and still others alert. We are jovial, restless, aroused, or depressed depending on what we have eaten. Society tacitly encourages certain behaviors that correspond to internal feelings, thereby encouraging the use of substances that produce acceptable behaviors.

• evolution
• drugs
• food
• plants
• behavior
• society
• brain chemistry
• social norms
• emotions