17. Denise M. Rousseau and others, "Not So Different After All: A Cross-Discipline View of Trust," Academy of Management Review 23, no. 3 (July 1998): 393404.

18. Ibid.

19. "Congress Less Popular than c.o.c.kroaches, Traffic Jams," Public Policy Polling, January 8, 2013, www.publicpolicypolling.com/main/2013/01/congress-less-popular-than-c.o.c.kroaches-traffic-jams.html.

Chapter 1.

1. Donja Darai and Silvia Gratz, "Golden b.a.l.l.s: A Prisoner's Dilemma Experiment," working paper (University of Zurich Socioeconomic Inst.i.tute, July 2010), accessed on September 13, 2013. There are a number of old episodes of the show available online. My personal favorite, "Golden b.a.l.l.s. The Weirdest Split or Steal Ever!," can be seen on YouTube, accessed on August 10, 2013, www.youtube.com/watch?v=S0qjK3TWZE8.

2. Over the years, there have been lots of imaginings of the Prisoner's Dilemma, and Split or Steal is essentially a one-shot dilemma. My favorite is James Gleick's creative description. See "Prisoner's Dilemma Has Unexpected Applications," New York Times, June 17, 1986, www.nytimes.com/1986/06/17/science/prisoner-s-dilemma-has-unexpected-applications.html. Also see descriptions of the Trust Game by Paul Zak and in Kay-Yut Chen and Marin Krakovsky, Secrets of the Moneylab: How Behavioral Economics Can Improve Your Business (New York: Portfolio, 2010).

3. Cristina Bicchieri, Erte Xiao, and Ryan Muldoon, "Trustworthiness Is a Social Norm, but Trusting Is Not," Politics Philosophy Economics 10, no. 2 (May 2011): 170187. Also see Colin F. Camerer, Behavioral Game Theory: Experiments in Strategic Interaction (Princeton, NJ: Princeton University Press, 2003).

4. See Paul Zak, Moral Molecule: The Source of Love and Prosperity (New York: Dutton, 2012). Zak told me that this series of Trust Game studies was done with college students.

5. L. Cameron and others, "Little Emperors: Behavioral Impacts of China's One-Child Policy," Science 339, no 6122 (February 2013): 953957.

6. Solitary Confinement: Hearing Before the Judiciary Subcommittee on the Const.i.tution, Civil Rights, and Human Rights, United States Senate, June 19, 2012, 112th Congress, statement of Craig Haney, professor of psychology, University of California, Santa Cruz, accessed on August 9, 2013, www.judiciary.senate.gov/pdf/12-6-19HaneyTestimony.pdf. Also see Atul Gawande, "h.e.l.lhole: The United States Holds Tens of Thousands of Inmates in Long-Term Solitary Confinement. Is This Torture?" New Yorker, March 30, 2009.

7. Michael S. Gazzaniga, Human: The Science Behind What Makes Us Unique (New York: HarperCollins, 2008).

8. R. A. Hill and P. C. Lee, "Predation Risk as an Influence on Group Size in Cercopithecoid Primates: Implications for Social Structure," Journal of Zoology 245 (1998): 447456.

9. John T. Cacioppo and William Patrick, Loneliness: Human Nature and the Need for Social Connection (New York: W. W. Norton & Company, 2008).

10. Matthew Lieberman, Social (New York: Crown, 2013). Also see David Brooks, "What Data Can't Do," New York Times, last modified February 18, 2013, http://www.nytimes.com/2013/02/19/opinion/brooks-what-data-cant-do.html.

11. Brooks, "What Data Can't Do."

12. Jonathan Haidt, The Righteous Mind: Why Good People Are Divided by Politics and Religion (New York: Vintage Books, 2012), xxii.

13. Roderick M. Kramer, "Rethinking Trust," Harvard Business Review, June 2009, hbr.org/2009/06/rethinking-trust.

14. Robert Kurzban, "The Social Psychophysics of Cooperation: Nonverbal Communication in a Public Goods Game," Journal of Nonverbal Behavior 25, no. 4 (2001): 241259.

15. My account of Stouffer's work relies on Joseph W. Ryan, "Samuel A. Stouffer and the American Soldier," Journal of Historical Biography 7 (Spring 2010): 100137, and Leonard Wong and others, "U.S. Army War College, Why They Fight: Combat Motivation in the Iraq War," Strategic Studies Inst.i.tute, July 1, 2003, www.strategicstudiesinst.i.tute.army.mil/pubs/display.cfm?pubID=179. I first came across Stouffer's work in Sebastian Junger, War (New York: Hachette Book Group, 2010).

16. Ryan, "Samuel A. Stouffer and the American Soldier."

17. Wong, "U.S. Army War College."

18. For the summary of the effects of social connections, I relied on Bert N. Uchino, "Understanding the Links Between Social Support and Physical Health: A Life-Span Perspective with Emphasis on the Separability of Perceived and Received Support," Perspectives on Psychological Science 4, no. 3 (2009): 236255. For the study on colds, see Sheldon Cohen and others, "Social Ties and Susceptibility to the Common Cold," JAMA 277, no. 24 (June 1997): 19401944. Also see George Vaillant, Triumphs of Experience: The Men of the Harvard Grant Study (Boston: Belknap Press, 2012).

19. Frans de Waal, The Age of Empathy: Nature's Lessons for a Kinder Society (New York: Broadway Books, 2010). I also interviewed de Waal in August 2012. Also see de Waal in Keltner, Smith, and Marsh, The Compa.s.sionate Instinct.

20. Robert H. Frank, Pa.s.sions Within Reason: The Strategic Role of the Emotions (New York: W. W. Norton & Company, 1988). Also see Gazzaniga, Human: The Science Behind What Makes Us Unique, 131. Also see Robert H. Frank, "The Status of Moral Emotions in Consequentialist Moral Reasoning" (Free Enterprise: Values in Action Conference Series, 20052006).

21. Peter Singer, The Expanding Circle: Ethics and Sociobiology (New York: Farrar, Straus and Giroux, February 1981). I first came across Singer's work in Steven Pinker, The Better Angels of Our Nature: Why Violence Has Declined (New York: Penguin Books, 2011).

22. Peter Singer, Writings on an Ethical Life (New York: Ecco Press, 2000), xix.

23. Martin A. Nowak, "Why We Help: The Evolution of Cooperation," Scientific American, June 19, 2012. I also relied on Nowak and Highfield, SuperCooperators. I interviewed Nowak in May 2012.

24. Ibid.

25. Sue Carter, professor of psychiatry and the codirector of the Brain Body Center, interview, July 2012. I also relied on her writings for my account. See, for instance, C. Sue Carter and Lowell L. Getz, "Monogamy and the Prairie Vole," Scientific American, 1993. I first came across Carter's story in Steven Johnson, Mind Wide Open: Your Brain and the Neuroscience of Everyday Life (New York: Scribner, 2004). Also see Larry Young and Brian Alexander, The Chemistry Between Us: Love, s.e.x, and the Science of Attraction (New York: Current, 2012).

26. Steven Johnson, Mind Wide Open.

27. My account relies on interviews with Zak and his description of the event in Moral Molecule, 22.

28. Paul J. Zak and Stephen Knack, "Trust and Growth," Economic Journal 111, no. 470 (March 2001): 295321.

29. Zak, Moral Molecule, 24.

30. Ibid., 13.

31. Adam Penenberg, "Social Networking Affects Brains Like Falling in Love," Fast Company, July/August 2010, www.fastcompany.com/1659062/social-networking-affects-brains-falling-love.

32. Michael Kosfeld and others, "Oxytocin Increases Trust in Humans," Nature 435 (June 2005): 673676.

33. Adam Penenberg, "Social Networking Affects Brains Like Falling in Love." Also see Michael Haederle, "The Best Fiscal Stimulus: Trust," Pacific Standard, August 2010. Haederle also didn't report feeling all that much after a dose of the hormone. I visited Zak's lab in May 2012.

34. Paul Zak argues that empathy promotes oxytocin release. I vetted this idea with other researchers.

35. M. Nagasawa and others, "Dog's Gaze at Its Owner Increases Owner's Urinary Oxytocin During Social Interaction," Hormones and Behavior 55, no. 3 (2009): 434441.

36. Patricia Churchland, Braintrust.

37. During the fact-checking process, de Dreu told me that "whether we can indeed call oxytocin a social glue is a bit oversimplifying (I may have done that, apologies). It would be better to say that oxytocin promotes social bonding with close others, including those seen as part of one's own group."

38. Adam J. Guastella, Philip B. Mitch.e.l.l, and Mark R. Daddsa, "Oxytocin Increases Gaze to the Eye Region of Human Faces," Biological Psychiatry 63, no. 1 (January 2008): 35.

39. Gregor Domes and others, "Oxytocin Improves 'Mind-Reading' in Humans," Biological Psychiatry 61, no. 6 (March 2007): 731733.

40. My account here relies on my interviews with Zak, and his account of the experiment in Moral Molecule. Also see Linda Geddes, "My Big Fat Nerd Wedding," New Scientist 205, no. 2747 (February 13, 2010): 3235.

41. Jennifer A. Bartz and others, "Social Effects of Oxytocin in Humans: Context and Person Matter," Trends in Cognitive Sciences 15, no. 7 (2011): 301309.

42. D. Scheele and others, "Oxytocin Modulates Social Distance Between Males and Females," Journal of Neuroscience 32, no. 46 (November 2012): 1607416079.

43. Ed Yong, "One Molecule for Love, Morality, and Prosperity?" Slate, July 17, 2012.

44. Carsten K. W. de Dreu and others, "Oxytocin Promotes Human Ethnocentrism," Proceedings of the National Academy of Sciences of the United States of America 108, no. 4 (2011): 12621266. I interviewed de Dreu in July 2012. Yong also mentions de Dreu's study.

45. Michael Kosfeld, "Brain Trust," in The Compa.s.sionate Instinct: The Science of Human Goodness, eds. Dacher Keltner, Jeremy Adam Smith, and Jason Marsh (New York: W. W. Norton & Company, 2010).

Chapter 2.

1. Stuart W. Sanders, Perryville Under Fire: The Aftermath of Kentucky's Largest Civil War Battle (Charleston, SC: History Press, 2012), 21.

2. St. John Richardson Liddell, Liddell's Record (Dayton, OH: Morningside House, 1985), 93.

3. My source for this account was John Fitch, Annals of the Army of the c.u.mberland (Philadelphia: J. B. Lippincott & Co, 1864). I first came across this story in Daniel N. Rolph, My Brother's Keeper: Union and Confederate Soldiers' Acts of Mercy During the Civil War (Mechanicsburg, PA: Stackpole Books, 2002). I also interviewed Rolph, historian and head of reference services at the Historical Society of Pennsylvania, in September 2012.

4. Duane Schultz, "Coming Together: Fredericksburg, 1862, for a Short Time, Soldiers Put Aside Their Weapons and Acted Like Friends," News Tribune (Tacoma, WA), December 9, 2012, www.thenewstribune.com/2012/12/09/2396239/coming-together-fredericksburg.html.

5. The detail about the Nashville Dispatch comes from James B. Jones Jr., Tennessee in the Civil War: Selected Contemporary Accounts of Military and Other Events, Month by Month (Jefferson, NC: McFarland & Company, 2011), 121.

6. Malcolm Brown and s.h.i.+rley Seaton served as my source for my description of the truces in the Napoleonic Wars, the Crimean War, and World War I. See "The Christmas Truce," BBC News, November 3, 1998, news.bbc.co.uk/2/hi/special_report/1998/10/98/world_war_i/197627.stm.

7. Robert Axelrod, The Evolution of Cooperation (New York: Basic Books, 1984).

8. Robert Axelrod, "Launching 'The Evolution of Cooperation,'" Journal of Theoretical Biology 299 (2012): 2124.

9. For more on non-zero-sum games, see Axelrod, Evolution of Cooperation, and Robert Wright, Nonzero: The Logic of Human Destiny (New York: First Vintage Books, 2000).

10. Adam Cohen, The Perfect Store: Inside eBay (New York: Little, Brown and Company, 2002), 18. My request to interview Pierre Omidyar was declined.

11. Cohen, The Perfect Store, cites "a study by the Pew Research Center that year found that just 8 percent of Americans felt comfortable using a credit card online," 26. And if you can't recall the Internet circa 1995, take a look at this: Chris Higgins, "What the Internet Looked Like in 1995," Mental Floss, last modified March 26, 2013, mentalfloss.com/article/49676/what-internet-looked-1995.

12. "Sp.a.w.ning e-trepreneurs," CNN Money, February 18, 1999, money.cnn.com/1999/02/18/fortune/fortune_ebay.

13. Cohen, The Perfect Store, 351.

14. Ibid.

15. Ibid.

16. Ibid., 27.

17. Ibid., 26.

18. "The Feedback Forum with Pierre Omidyar," OnInnovation, last modified March 2008, www.oninnovation.com/videos/detail.aspx?video=1268&t.i.tle=The%20Feedback%20Forum.

19. Nowak and Highfield, SuperCooperators, 5253.

20. Ibid.

21. Donald W. Pfaff, The Neuroscience of Fair Play: Why We (Usually) Follow the Golden Rule (New York: Dana Press, 2007), 10.

22. Nowak and Highfield, SuperCooperators.

23. "The Feedback Forum with Pierre Omidyar."

24. For the idea of using Charlie Brown to highlight game theory, I am indebted to Avinash K. Dixit and Barry J. Nalebuff, The Art of Strategy: A Game Theorist's Guide to Success in Business and Life (New York: W. W. Norton & Company, 2008). Also see Presh Talwalkar, "Charlie Brown and Game Theory," Mind Your Decisions, accessed on August 12, 2013, mindyourdecisions.com/blog/2009/11/24/charlie-brown-and-game-theory/#.Ud3WYUHvvzg.

25. Robert Frank and Ben Bernanke, Principles of Microeconomics (New York: McGraw-Hill/Irwin, 2008), define a commitment problem as "a situation in which people cannot achieve their goals because of an inability to make credible threats or promises," 267. Also see "Commitment Problems," Game Theory 101, accessed on October 10, 2013, gametheory101.com/Commitment_Problems.html.

26. "Commitment Problems and Devices," Experimental Economics Center, Andrew Young School of Policy Studies at Georgia State University, accessed on August 12, 2013, www.econport.org/content/teaching/modules/NFG/Commit.html.

27. Al Kamen, "Punching Their Tickets," Was.h.i.+ngton Post, May 12, 1997, appears to have come up with the term Great New York City Parking War. My account of this so-called war relies on Raymond Fisman and Edward Miguel, "Cultures of Corruption: Evidence from Diplomatic Parking Tickets," Working Paper no. 12312 (National Bureau of Economic Research, June 2006), accessed on September 13, 2013, www.nber.org/papers/w12312, as well as other news accounts.

28. John Goldman, "Powell Brokers Parking Peace," Los Angeles Times, August 10, 2002, articles.latimes.com/2002/aug/10/nation/na-parking10.

29. Fisman and Miguel, "Cultures of Corruption: Evidence from Diplomatic Parking Tickets."

30. Raymond Fisman, "Reforming Tony Soprano's Morals," Forbes, May 6, 2006, www.forbes.com/forbes/2006/0522/040.html.

31. Rand, Greene, and Nowak, "Spontaneous Giving and Calculated Greed."

32. Kahneman, Thinking, Fast and Slow (New York: Farrar, Straus and Giroux, 2011).

33. Schneier, Liars and Outliers, gives one of the best summaries of how societies induce cooperation, though Schneier doesn't spend much time on the notion of reciprocity or indirect reciprocity.

34. Ken Lee, "Why Is Paris Hilton Still Driving?," People, May 9, 2007, www.people.com/people/article/0,,20038364,00.html. Also see TMZ Staff, "Exclusive: Paris Busted for DUI," TMZ, September 7, 2006, www.tmz.com/2006/09/07/exclusive-paris-busted-for-dui.

35. Cal Fussman, "Paris Hilton: What I've Learned," Esquire, December 17, 2008, www.esquire.com/features/what-ive-learned/paris-hilton-quotes-0109.

36. I came across Ramirez's story in Jordan Ellenberg, "You Can't Trust Airport Security," Wall Street Journal (September 2, 2012). I interviewed Hector Ramirez in April 2013. I also relied on Tina Redine, "Subway Operator Recalls 9/11 Cortlandt Street Stop Rescue," NY1, September 10, 2011. Also see Harvey Molotch, Against Security (New York: Wiley, 2012).

Chapter 3.

1. For information on the Rockefeller case, I relied on Mark Seal, The Man in the Rockefeller Suit: The Astonis.h.i.+ng Rise and Spectacular Fall of a Serial Impostor (New York: Penguin Group, 2011), Kindle edition. Also helpful were Mark Seal, "The Man in the Rockefeller Suit," Vanity Fair, January 2009, and Commonwealth v. Gerhartsreiter, Case No. 10-P-1899, available at http://www.courthousenews.com/AppellateOpinions/10P1899.doc. I also consulted news articles and interviewed Seal in October 2012. I spoke to Rockefeller's lawyer, Brad Bailey, who told me that he had advised Rockefeller not to speak to the media. I also sent a letter to Clark Rockefeller. He did not respond.

2. Seal, The Man in the Rockefeller Suit, 2516. Also see Walter Kirn, "Pedigree," New Yorker, June 10, 2013.

3. Jonathan Saltzman and Andrew Ryan, "'Rockefeller' Said He Had New Wife," Boston Globe, May 29, 2009, www.boston.com/news/local/ma.s.sachusetts/articles/2009/05/29/rockefeller_claimed_he_had_new_wife_social_worker_testifies/?page=full. Also see David Schoetz, "Amber Alert Off, Little Girl Still Missing," ABC News, July 28, 2008, abcnews.go.com/US/story?id=5462371&page=2.

4. Seal, The Man in the Rockefeller Suit, 780.