If the right kind of smile is synonymous with happiness: D. Keltner et al., “Facial Expression of Emotion,” Handbook of Affective Science, ed. Richard Davidson, Klaus Scherer, and Hill H. Goldsmith, (London: Oxford University Press, 2003), 415–32.
Charles Darwin’s analysis of the smile: Darwin, Expression, chap. 8.
In her careful observations of primates: S. Preuschoft and J. A. R.A. M. Van Hooff, “The Social Function of ‘Smile’ and ‘Laughter:’ Variations across Primate Species and Societies,” in Where Nature Meets Culture: Nonverbal Communication in Social Interaction, ed. U. Segerstråle and P. Molnár, (Hillsdale, NJ: Erlbaum, 1997), 171–89.
I first encountered the deferential smile: D. Keltner et al., “Teasing in Hierarchical and Intimate Relations,” Journal of Personality and Social Psychology 75 (1998): 1231–47.
Research shows that when workers smile in the service industry: For a review of the role of emotion in the workplace, see M. W. Morris and D. Keltner, “How Emotions Work: An Analysis of the Social Functions of Emotional Expression in Negotiations,” Review of Organizational Behavior 22 (2000): 1–50.
workers experience a problematic disconnect: Arlie R. Hochschild, The Managed Heart: Commercialization of Human Feeling (Berkeley: University of California Press, 1983).
This disconnect has parallels to recent studies by my colleague Ann Kring of schizophrenics: A. M. Kring, S. L. Kerr, A. D. Smith, and J. M. Neale, “Flat Affect in Schizophrenia Does Not Reflect Diminished Subjective Experience of Emotion,” Journal of Abnormal Psychology 102 (1993): 507–17; Kring and Neale, “Do Schizophrenics Show a Disjunctive Relationship among Expressive, Experiential, and Psychophysiological Components of Emotion?” Journal of Abnormal Psychology 105 (1996): 249–57.
the empirical literature on the smile yields similarly paradoxical findings: Keltner et al., “Facial Expression of Emotion,” in Handbook of Affective Sciences, 415–32.
The answer is provided by Paul Ekman, and it involves looking away from the lip corners: Frank, Ekman, and Friesen, “Behavioral Markers and Recognizability of the Smile of Enjoyment,” Journal of Personality and Social Psychology 64 (1993): 83–93.
Duchenne smiles differ morphologically: ibid., 83.
D smiles tend to be associated with activity in the left anterior portion of the frontal lobes: Neuroscientist Richard Davidson has made the persuasive case that positive emotions tend to activate regions of the brain on the left side of the frontal lobes, because these regions enable the individual to approach rewards. Ekman, Davidson, and Friesen, “The Duchenne Smile: Emotional Expression and Brain Physiology II,” Journal of Personality and Social Psychology 58 (1996): 342–53.
When a ten-month-old is approached by his or her mother: Davidson and N. A. Fox, “Frontal Brain Asymmetry Predicts Infants’ Response to Maternal Separation,” Journal of Abnormal Psychology 98 (1989): 127–31.
we interviewed middle-aged adults six months after their deceased spouse had passed away: D. Keltner and G. A. Bonanno, “A Study of Laughter and Dissociation: The Distinct Correlates of Laughter and Smiling During Bereavement,” Journal of Personality and Social Psychology 73 (1997): 687–702.
In Emotions Revealed: Paul Ekman, Emotions Revealed (New York: Owl, 2004).
In the 1980s developmental psychologists: E. Z. Tronick, “Emotions and Emotional Communications in Infants,” American Psychologist 44 (1989): 112–19; Tronick, J. Cohn, and E. Shea, “The Transfer of Affect between Mothers and Infants,” Affective Development in Infancy, ed. T. B. Brazelton and M. W. Yogman (Norwood, NJ: Ablex, 1986); T. Field et al., “Behavior State Matching and Synchrony in Mother-Infant Interactions of Nondepressed Versus Depressed Dyads,” Developmental Psychology 26 (1990): 7–14; Field et al., “Infants of Depressed Mothers Show ‘Depressed’ Behavior Even with Nondepressed Adults,” Child Development 59 (1988): 1569–79.
Friends of depressives: Connie Hammen and Ian Gotlib have done superb work documenting the social costs of depression, how it transmits to others and turns relationships into more complex, and at times less rewarding, endeavors. One likely reason is that depressives give off fewer positive emotional cues, in such behaviors as the smile, laugh, and playful touch. Ian H. Gotlib and Constance L. Hammen, Psychological Aspects of Depression: Toward a Cognitive-Interpersonal Integration (Chichester: Wiley, 1992).
In conversations with individuals who show little positive emotion in the face or voice: For a review of these findings, see Keltner and Kring, “Emotion, Social Function, and Psychopathology.”
will eagerly cross the surface, risking potential harm, to be in the warm, reassuring midst of their mother’s smile: J. F. Sorce, R. N. Emde, Joseph Campos, and M. D. Klinnert, “Maternal Emotional Signaling: Its Effect on the Visual Cliff Behavior of One-Year-Olds,” Developmental Psychiatry 21 (1985): 195–200; M. D. Klinnert, R. N. Emde, P. Butterfield, J. Campos, “Social Referencing: The Infant’s Use of Emotional Signals from a Friendly Adult with Mother Present,” Developmental Psychology 22 (1986): 427–32.
when people emit D smiles when experiencing stress: B. L. Fredrickson and R. W. Levenson, “Positive Emotions Speed Recovery from the Cardiovascular Sequelae of Negative Emotions,” Cognition and Emotion 12 (1998): 191–220.
The definitive work on this topic: For a review of this superb work, see U. Dimberg and A. Öhman, “Behold the Wrath: Psychophysiological Responses to Facial Stimuli,” Motivation and Emotion 20 (1996): 149–82.
suggest that perceiving smiles in others, most likely of the Duchenne variety, triggers the release of the neurotransmitter dopamine: R. Depue and J. Morrone-Strupinsky, “A Neurobehavioral Model of Affiliative Bonding: Implications for Conceptualizing a Human Trait of Affiliation,” Behavioral and Brain Sciences 28 (2005): 313–95.
As one illustration: C. Senior, “Beauty in the Brain of the Beholder,” Neuron 38 (2004): 525–28.
Undaunted, LeeAnne Harker and I took a week to code the yearbook photos: L. A. Harker and D. Keltner, “Expressions of Positive Emotion in Women’s College Yearbook Pictures and their Relationship to Personality and Life Outcomes across Adulthood,” Journal of Personality and Social Psychology 80 (2001): 112–24.
Dozens of scientific studies have found that people who are led to experience brief positive emotions are more creative: Research by Alice Isen and Barbara Fredrickson dispels many myths about the thoughtlessness of positive emotion. Instead, the consistent theme to emerge is that positive emotions make our thought processes more creative and sophisticated. Fredrickson, “What Good Are Positive Emotions?” Review of General Psychology 2 (1998): 300–19, and “The Role of Positive Emotions in Positive Psychology: The Broaden-and-Build Theory of Positive Emotions,” American Psychologist 56 (2001): 218–26; A. M. Isen, K. A. Daubman, and G. P. Nowicki, “Positive Affect Facilitates Creative Problem Solving,” Journal of Personality and Social Psychology 52 (1987): 1122–31; A. M. Isen, “Positive Affect, Cognitive Processes, and Social Behavior,” in Advances in Experimental Social Psychology, ed. Leonard Berkowitz (New York: Academic Press, 1987), 203–53.