"The Expression of the Emotions in Man and Animals" by Charles Darwin is a scientific work published in 1872. Darwin's third major evolutionary study examines the biological origins of human emotional behavior—from smiling and frowning to blushing and surprise. Challenging traditional spiritual explanations, Darwin traces these expressions to animal behavior and argues for their universal nature across all human cultures. Using innovative methods including questionnaires, psychological experiments, and pioneering photography, Darwin establishes connections between mental states and physical movement, forming what some consider the foundation of modern scientific psychology.