21. public speaking is the number-one fear: Victoria Cunningham, Morty Lefkoe, and Lee Sechrest, "Eliminating Fears: An Intervention that Permanently Eliminates the Fear of Public Speaking," Clinical Psychology and Psychotherapy 13 (2006): 18393.

22. Public speaking phobia has many causes: Gregory Berns, Iconoclast: A Neuroscientist Reveals How to Think Differently (Boston, MA: Harvard Business Press, 2008), 5981.

23. introverts are significantly more likely: Susan K. Opt and Donald A. Loffredo, "Rethinking Communication Apprehension: A Myers-Briggs Perspective," Journal of Psychology 134, no. 5 (2000): 55670. See also Michael J. Beatty, James C. McCroskey, and Alan D. Heisel, "Communication Apprehension as Temperamental Expression: A Communibiological Paradigm," Communication Monographs 65 (1998): 197219. See also Peter D. Macintyre and Kimly A. Thivierge, "The Effects of Speaker Personality on Antic.i.p.ated Reactions to Public Speaking," Communication Research Reports 12, no. 2 (1995): 12533.

24. in a group of people, on average half of the variability: David G. Winter, Personality, 512.

25. temperature or humidity: Natasha Mitch.e.l.l, "Jerome Kagan: The Father of Temperament," radio interview with Mitch.e.l.l on ABC Radio International, August 26, 2006 (accessed at http://www.abc.net.au/rn/allinthemind/stories/2006/1722388.htm).

26. "climb a few fences ... danger and excitement": Gallagher (quoting Lykken), "How We Become What We Are."

27. "The university is filled with introverts": Interview with the author, June 15, 2006.

28. if raised by attentive families in safe environments ... "twigs on the same genetic branch": Winifred Gallagher, I.D.: How Heredity and Experience Make You Who You Are (New York: Random House, 1996), 29, 4650. See also Kagan and Snidman, The Long Shadow of Temperament, 5.

29. kids acquire their sense of right and wrong: Grazyna Kochanska and R. A. Thompson, "The Emergence and Development of Conscience in Toddlerhood and Early Childhood," in Parenting and Children's Internalization of Values, edited by J. E. Grusec and L. Kucynski (New York: John Wiley and Sons), 61. See also Grazyna Kochanska, "Toward a Synthesis of Parental Socialization and Child Temperament in Early Development of Conscience," Child Development 64 no. 2 (1993): 32547; Grazyna Kochanska and Nazan Aksan, "Children's Conscience and Self-Regulation," Journal of Personality 74, no. 6 (2006): 15871617; Grazyna Kochanska et al., "Guilt and Effortful Control: Two Mechanisms That Prevent Disruptive Developmental Trajectories," Journal of Personality and Social Psychology 97, no. 2 (2009): 32233.

30. tragedy of a bold and exuberant temperament: Gallagher, I.D., 4650.

31. dubbed "the orchid hypothesis": David Dobbs, "The Science of Success," The Atlantic magazine, 2009. See also Jay Belsky et al., "Vulnerability Genes or Plasticity Genes?" Molecular Psychiatry, 2009: 19; Michael Pluess and Jay Belsky, "Differential Susceptibility to Rearing Experience: The Case of Childcare," The Journal of Child Psychology and Psychiatry 50, no. 4 (2009): 396404; Pluess and Belsky, "Differential Susceptibility to Rearing Experience: Parenting and Quality Child Care," Developmental Psychology 46, no. 2 (2010): 37990; Jay Belsky and Michael Pluess, "Beyond Diathesis Stress: Differential Susceptibility to Environmental Influences," Psychological Bulletin 135, no. 6 (2009): 885908; Bruce J. Ellis and W. Thomas Boyce, "Biological Sensitivity to Context," Current Directions in Psychological Science 17, no. 3 (2008): 18387.

32. with depression, anxiety, and shyness: Aron, Psychotherapy and the Highly Sensitive Person, 3. See also A. Engfer, "Antecedents and Consequences of Shyness in Boys and Girls: A 6-year Longitudinal Study," in Social Withdrawal, Inhibition, and Shyness in Childhood, edited by K. H. Rubin and J. B. Asendorpf (Hillsdale, NJ: Lawrence Erlbaum, 1993), 4979; W. T. Boyce et al., "Psychobiologic Reactivity to Stress and Childhood Respiratory Illnesses: Results of Two Prospective Studies," Psychosomatic Medicine 57 (1995): 41122; L. Gannon et al., "The Mediating Effects of Psychophysiological Reactivity and Recovery on the Relationship Between Environmental Stress and Illness," Journal of Psychosomatic Research 33 (1989): 16575.

33. Indeed, about a quarter of Kagan's high-reactive kids: E-mail from Kagan to the author, June 22, 2010.

34. good parenting, child care, and a stable home environment: See, for example, Belsky et al., "Vulnerability Genes or Plasticity Genes?", 5. See also Pluess and Belsky, "Differential Susceptibility to Rearing Experience: The Case of Childcare," 397.

35. kind, conscientious: Aron, The Highly Sensitive Child.

36. They don't necessarily turn into cla.s.s presidents: Author interview with Jay Belsky, April 28, 2010.

37. world of rhesus monkeys: Stephen J. Suomi, "Early Determinants of Behaviour: Evidence from Primate Studies," British Medical Bulletin 53, no. 1 (1997): 17084 ("high-reactive infants cross-fostered to nurturant females actually appeared to be behaviourally precocious.... These individuals became especially adept at recruiting and retaining other group members as allies in response to agonistic encounters and, perhaps as a consequence, they subsequently rose to and maintained top positions in the group's dominance hierarchy.... Clearly, high-reactivity need not always be a.s.sociated with adverse short- and long-term outcomes," p. 180). See also this video on the Atlantic Monthly website: (http://www.theatlantic.com/magazine/archive/2009/12/the-science-of-success/7761/), in which Suomi tells us that "the monkeys who had that same short allele and grew up with good mothers had no problems whatsoever. They turned out as well or better than monkeys who had the other version of this gene." (Note also that the link between the short allele of the SERT gene and depression in humans is well discussed but somewhat controversial.)

38. thought to be a.s.sociated with high reactivity and introversion: Seth J. Gillihan et al., "a.s.sociation Between Serotonin Transporter Genotype and Extraversion," Psychiatric Genetics 17, no. 6 (2007): 35154. See also M. R. Munafo et al., "Genetic Polymorphisms and Personality in Healthy Adults: A Systematic Review and Meta-a.n.a.lysis," Molecular Psychiatry 8 (2003): 47184. And see Cecilie L. Licht et al., "a.s.sociation Between Sensory Processing Sensitivity and the 5-HTTLPR Short/Short Genotype."

39. has speculated that these high-reactive monkeys: Dobbs, "The Science of Success."

40. adolescent girls with the short allele of the SERT gene ... less anxiety on calm days: Belsky et al., "Vulnerability Genes or Plasticity Genes?"

41. this difference remains at age five: Elaine Aron, Psychotherapy and the Highly Sensitive Person, 24041.

42. even more resistant than other kids: Boyce, "Psychobiologic Reactivity to Stress and Childhood Respiratory Illnesses: Results of Two Prospective Studies." See also W. Thomas Boyce and Bruce J. Ellis, "Biological Sensitivity to Context: I. Evolutionary-Developmental Theory of the Origins and Functions of Stress Reactivity," Development and Psychopathology 27 (2005): 283.

43. The short allele of the SERT gene: See Judith R. Homberg and Klaus-Peter Lesch, "Looking on the Bright Side of Serotonin Transporter Gene Variation," Biological Psychiatry, 2010.

44. "sailors are so busy-and wisely-looking under the water line": Belsky et al., "Vulnerability Genes or Plasticity Genes?"

45. "The time and effort they invest": Author interview with Jay Belsky, April 28, 2010.

CHAPTER 5: BEYOND TEMPERAMENT

1. "Enjoyment appears at the boundary": Mihaly Csikszentmihalyi, Flow: The Psychology of Optimal Experience (New York: Harper Perennial, 1990), 52.

2. windowless room with Dr. Carl Schwartz: I conducted a series of interviews with Dr. Schwartz between 2006 and 2010.

3. the footprint of a high- or low-reactive temperament: Carl Schwartz et al., "Inhibited and Uninhibited Infants 'Grown Up': Adult Amygdalar Response to Novelty," Science 300, no. 5627 (2003): 195253.

4. If you were a high-reactive baby: For a good overview of the relationship between the amygdala and the prefrontal cortex, see Joseph Ledoux, The Emotional Brain: The Mysterious Underpinnings of Emotional Life (New York: Simon & Schuster, 1996), chapters 6 and 8. See also Gregory Berns, Iconoclast: A Neuroscientist Reveals How to Think Differently (Boston, MA: Harvard Business Press, 2008), 5981.

5. self-talk to rea.s.sess upsetting situations: Kevin N. Ochsner et al., "Rethinking Feelings: An fMRI Study of the Cognitive Regulation of Emotion," Journal of Cognitive Neuroscience 14, no. 8 (2002): 121529.

6. scientists conditioned a rat: Ledoux, The Emotional Brain, 24849.

7. Hans Eysenck: David C. Funder, The Personality Puzzle (New York: W. W. Norton, 2010), 28083.

8. high arousal levels in the brain: E-mail from Jerome Kagan to the author, June 23, 2010.

9. many different kinds of arousal: E-mail from Carl Schwartz to the author, August 16, 2010. Also note that introverts seem not to be in a baseline state of high arousal so much as susceptible to tipping over into that state.

10. excited fans at a soccer game: E-mail from Jerome Kagan to the author, June 23, 2010.

11. a host of evidence that introverts are more sensitive: This has been written about in many places. See, for example, Robert Stelmack, "On Personality and Arousal: A Historical Perspective on Eysenck and Zuckerman," in On the Psychobiology of Personality: Essays in Honor of Marvin Zuckerman, edited by Marvin Zuckerman and Robert Stelmack (Pergamon, 2005), 1728. See also Gerald Matthews et al., Personality Traits (Cambridge, UK: Cambridge University Press, 2003), 16970, 18689, 32942. See also Randy J. La.r.s.en and David M. Buss, Personality Psychology: Domains of Knowledge About Human Nature (New York: McGraw Hill, 2005), 2026.

12. lemon juice: Funder, The Personality Puzzle, 281.

13. noise level preferred by the extroverts: Russell G. Geen, "Preferred Stimulation Levels in Introverts and Extroverts: Effects on Arousal and Performance," Journal of Personality and Social Psychology 46, no. 6 (1984): 130312.

14. They can hunt for homes: This idea comes from Winifred Gallagher, House Thinking: A Room-by-Room Look at How We Live (New York: Harper Collins, 2006).

15. introverts function better than extroverts when sleep deprived: William Kilgore et al., "The Trait of Introversion-Extraversion Predicts Vulnerability to Sleep Deprivation," Journal of Sleep Research 16, no. 4 (2007): 35463.

16. Drowsy extroverts behind the wheel: Matthews, Personality Traits, 337.

17. Overarousal interferes with attention: Gerald Matthews and Lisa Dorn, "Cognitive and Attentional Processes in Personality and Intelligence," in International Handbook of Personality and Intelligence, edited by Donald H. Saklofske and Moshe Zeidner (New York: Plenum Press, 1995): 36796. Or, as the psychologist Brian Little puts it, "extraverts often find that they are able to handle cramming for speeches or briefings in a way that would be disastrous for introverts."

18. a cycle of dread, fear, and shame: Berns, Iconoclast, 5981.

CHAPTER 6: "FRANKLIN WAS A POLITICIAN, BUT ELEANOR SPOKE OUT OF CONSCIENCE"