Amusement is the state of experiencing humorous and entertaining events or situations while the person or animal actively maintains the experience, and is associated with enjoyment, happiness, laughter and pleasure. It is an emotion with positive valence and high physiological arousal. Amusement is considered an "epistemological" emotion because humor occurs when one experiences a cognitive shift from one knowledge structure about a target to another, such as hearing the punchline of a joke. The pleasant surprise that happens from learning this new information leads to a state of amusement which people often express through smiling, laughter or chuckling. Current studies have not yet reached consensus on the exact purpose of amusement, though theories have been advanced in the fields of psychology, psychiatry, and sociology. In addition, the precise mechanism that causes a given element (image, sound, behavior, etc.) to be perceived as more or less 'amusing' than another similar element to a particular individual is not clearly understood. Theories Two different theoretical perspectives about emotion provide contrasting origins of amusement: Evolutionary The evolutionary perspective proposes that amusement is a distinct emotion that evolved to enhance a species’ survival. Collective laughter helps define an ingroup, helping people recognize those similar to them and feel included. It also helps identify outgroup members and enhance the barrier between the two. Laughter can provide network support as encouragement, or it can inform ingroup members that they are losing majority favor and to adjust their behavior to reassimilate. Constructed emotion The theory of constructed emotion suggests that when humans have a positive experience that increases their arousal, such as a faster heartbeat and increased sweat production, they cognitively seek out a label for that feeling. They will land on amusement if that experience resembles other amusement experiences they have had. Emotional expression of amusement The origin of the study of emotional expression is often attributed to Charles Darwin. In 1872, Darwin published his book The Expression of the Emotions in Man and Animals, in which he extensively describes his observations of how people and animals display emotions on their faces and through sound. Darwin comments on amusement as an emotion of great joy during which a person is likely to laugh. He also notes that across all peoples humans can laugh until they are panting and tears roll down their cheeks. In the 1960s, Paul Ekman, an American psychologist, revived the study of emotional expression,