Kelly D. Brownell's Open Yale Courses lecture continues the survey of why humans eat the way they do, tracing the biological drives that evolved to seek out calorie-dense food and the psychological habits that keep people eating past hunger. The session sits within a course that treats obesity and diet not as personal failings but as outcomes of an environment engineered by the food industry, advertising, and agricultural policy. Expect discussion of appetite regulation, taste preference, and how economic incentives shape what ends up on supermarket shelves and in school cafeterias. Brownell draws on his background in clinical psychology and public health to connect individual eating behavior to larger political fights over food labeling, subsidies, and regulation. The lecture is part of a full Yale course sequence, so it assumes some familiarity with earlier sessions but stands on its own as an account of how biology, psychology, and policy combine to produce the modern American diet.