The Expression of the Emotions in Man and Animals is Charles Darwin's major work of evolutionary theory. The book concerns the biological aspects of emotional life, and Darwin explores the animal origins of such human characteristics as the lifting of the eyebrows in moments of surprise and the mental confusion which typically accompanies blushing. Darwin's biological approach links emotions to their origins in animal behavior, and allows cultural factors only an auxiliary role in the shaping of expression. This biological emphasis leads to a concentration on six emotional states: happiness, sadness, fear, anger, surprise and disgust.It also leads to an appreciation of the universal nature of expression, with its implication of a single origin for the entire human species; and Darwin points to the importance of emotional communication with children in their psychological development.