Emotion. A pleasant visceral, emotional feeling of contentment, well-being, or joy.
Usage: Happiness may show in a. the laugh, and in b. the smile. (N.B.: Intense joy may also show in crying.) Unlike most other facial signs of emotion, the smile is subject to learning and conscious control. In the U.S., Japan, and many other societies, children are taught to smile on purpose, e.g., in a courteous greeting, whether or not they actually feel happy.
RESEARCH REPORTS: 1. Signs of intense joy include "purposeless movements" (e.g., dancing about and clapping hands), loud laughter, and weeping (Darwin 1872:175, 195). 2.Happiness shows most clearly in the lower face and eye area (Ekman, Friesen, and Tomkins 1971). 3. Facial expressions of joy emerge in human infants between five and seven months of age (Burgoon et al. 1989:349).
Evolution. Happiness is a mammalian elaboration a. of feelings of well-being and contentment related to parasympathetic digestion (see ENTERIC BRAIN, REST-AND-DIGEST), and b.of arousal due to stimulation of pleasure areas of the brain.
Anatomy. Motion energy maps suggest that, facially, happiness is expressed primarily with the mouth. A happy face appears when zygomaticus major muscles draw the angle of our lips backward and upward into a grin. Levator anguli oris may also exhibit our teeth. In the true (i.e., involuntary) smile, lip movements show in tandem with contractions of orbicularis oculi muscles, which crinkle the skin around the outside corners of our eyes, forming "crow's feet" or smiling eyes.
Great apes. Research by University of Warwick behavioral economist, Andrew Oswald and colleagues, published in the Proceedings of the National Academy of Sciences (Nov. 26, 2012), reports that the human being's midlife crisis--a near universal reduction in happiness levels in life's middle years--is also experienced by chimpanzees and orangutans.
Philosophy. In The Conquest of Happiness, Bertrand Russell distinguishes between "animal happiness" (possible for any human being) and "spiritual happiness" (only for those humans who can read and write).
Neuro-notes. The true or "heartfelt" smile is controlled by the anterior cingulate gyrus of the limbic system through paleocircuits of the basal ganglia.
Photo of "Smile, Surfacing" (Fiesta Mexicana, Spokane, Washington, USA) by Doreen K. Givens (copyright 2007)