Up to now, the monkeys appeared to be as rational as humans in their use of money. But surely this last experiment showed the vast gulf that lay between monkey and man.

Or did it?

The fact is that similar experiments with human beings-day traders, for instance-had found that people make the same kind of irrational decisions at a nearly identical rate. The data generated by the capuchin monkeys, Chen says, "make them statistically indistinguishable from most stock-market investors."

So the parallels between human beings and these tiny-brained, food-and-s.e.x monkeys remained intact. And then, as if Chen needed any further evidence of these parallels, the strangest thing happened in the lab.

Felix scurried into the testing chamber, just as he'd done countless times before, but on this day, for reasons Chen could never understand, Felix did not gather up the twelve coins on the tray and use them to buy food. Instead, he flung the entire tray's worth of coins back into the communal cage and, fleeing the testing chamber, dashed in after them-a bank heist followed by a jailbreak.

There was chaos in the big cage, with twelve coins on the floor and seven monkeys going after them. When Chen and the other researchers went inside to get the coins, the monkeys wouldn't give them up. After all, they had learned that the coins had value. So the humans resorted to bribing the capuchins with treats. This taught the monkeys another valuable lesson: crime pays.

Then, out of the corner of his eye, Chen saw something remarkable. One monkey, rather than handing his coin over to the humans for a grape or a slice of apple, instead approached a second monkey and gave it to her. Chen had done earlier research in which monkeys were found to be altruistic. Had he just witnessed an unprompted act of monkey altruism?

After a few seconds of grooming-bam!-the two capuchins were having s.e.x.

What Chen had seen wasn't altruism at all, but rather the first instance of monkey prost.i.tution in the recorded history of science.

And then, just to prove how thoroughly the monkeys had a.s.similated the concept of money, as soon as the s.e.x was over-it lasted about eight seconds; they're monkeys, after all-the capuchin who'd received the coin promptly brought it over to Chen to purchase some grapes.

This episode sent Chen's mind spinning. Until now, the researchers had run narrowly defined money experiments with one monkey at a time. What if Chen could introduce money directly into the monkeys' lives? The research possibilities were endless.

Alas, Chen's dream of capuchin capitalism never came to pa.s.s. The authorities who oversaw the monkey lab feared that introducing money to the capuchins would irreparably damage their social structure.

They were probably right.

If the capuchins were so quick to turn to prost.i.tution as soon as they got hold of some money, just imagine how quickly the world would be overrun with monkey murderers and monkey terrorists, with monkey polluters who contribute to global warming and monkey doctors who fail to wash their hands. Future generations of monkeys, of course, would come along and solve these problems. But there would always be something to fix-like the monkeys' pigheaded insistence that all their children ride in car seats...

ACKNOWLEDGMENTS

Jointly, we'd first like to thank all the people who let us tell their stories in this book. For every person named in the text, there were usually five or ten more who contributed in various ways. Thanks to all of you. We are also greatly indebted to the many scholars and researchers whose work is cited in the book.

Suzanne Gluck of William Morris Endeavor is an agent like no other, and we are lucky to have her. She has many extraordinary colleagues, including Tracy Fisher, Raffaella De Angelis, Cathryn Summerhayes, Erin Malone, Sarah Ceglarski, Caroline Donofrio, and Eric Zohn, all of whom have been a big help, as have others at WME, past and present.

At William Morrow/HarperCollins, we've had a great time working with our wonderful editor Henry Ferris, and Dee Dee DeBartlo is unfailingly hardworking and cheerful. There are many others to thank-Brian Murray, Michael Morrison, Liate Stehlik, Lynn Grady, Peter Hubbard, Danny Goldstein, and Frank Albanese among them-as well as those who've moved on, especially Jane Friedman and Lisa Gallagher. For tea, sympathy, and more, thanks to Will Goodlad and Stefan McGrath at Penguin UK (who also provide excellent British children's books for our offspring).

The New York Times has allowed us, in its pages and on our blog, to run some of this book's ideas up the flagpole. Thanks especially to Gerry Marzorati, Paul Tough, Aaron Retica, Andy Rosenthal, David Shipley, Sasha Koren, Jason Kleinman, Brian Ernst, and Jeremy Zilar.

To the women of Number 17: what fun! And there is more to come.

The Harry Walker Agency has given us more opportunities to meet more incredible people than we ever thought possible, and they are a joy to work with. Thanks to Don Walker, Beth Gargano, Cynthia Rice, Kim Nisbet, Mirjana Novkovic, and everyone else there.

Linda Jines continues to prove that she has no peer when it comes to naming things.

And thanks especially to all the readers who take the time to send along their clever, fascinating, devious, and maddening ideas for us to pursue.

PERSONAL ACKNOWLEDGMENTS

I owe an enormous debt to my many co-authors and colleagues, whose great ideas fill this book, and to all the kind people who have taken the time to teach me what I know about economics and life. My wife, Jeannette, and our children, Amanda, Olivia, Nicholas, and Sophie, make every day a joy, even though we miss Andrew so much. I thank my parents, who showed me it was okay to be different. Most of all, I want to thank my good friend and co-author Stephen Dubner, who is a brilliant writer and a creative genius.

S.D.L.

People like Sudhir Venkatesh, Allie, Craig Feied, Ian Horsley, Joe De May Jr., John List, Nathan Myhrvold, and Lowell Wood make me grateful every day that I became a writer. They are full of insights and surprises that are a joy to learn. Steve Levitt is not only a great collaborator but a wonderful economics teacher as well. For outstanding research a.s.sistance, thanks to Rhena Tantisunthorn, Rachel Fershleiser, Nicole Tourtelot, Danielle Holtz, and especially Ryan Hagen, who did great work on this book and will write great books of his own one day. To Ellen, my extraordinary wife, and to the fantastic creatures known as Solomon and Anya: you are all pretty d.a.m.n swell.

S.J.D.

NOTES

INTRODUCTION: PUTTING THE FREAK IN ECONOMICS

THE PERILS OF WALKING DRUNK: The brilliant economist Kevin Murphy called our attention to the relative risk of walking drunk. For background on the dangers of drunk driving, see Steven D. Levitt and Jack Porter, "How Dangerous Are Drinking Drivers?" Journal of Political Economy 109, no. 6 (2001). / 2 One of the benefits of a c.u.mbersome federal bureaucracy is that it hires tens of thousands of employees to staff hundreds of agencies that collect and organize endless reams of statistical data. The National Highway Traffic Safety Administration (NHTSA) is one such agency, and it supplies definitive and valuable data on traffic safety. Regarding the proportion of miles driven drunk, see "Impaired Driving in the United States," NHTSA, 2006. / 2 For drunk pedestrian deaths, see "Pedestrian Roadway Fatalities," NHTSA, DOT HS 809 456, April 2003. / 2 For drunk driving deaths, see "Traffic Safety Facts 2006," NHTSA, DOT HS 810 801, March 2008. / 2 "They lie down to rest on country roads": see William E. Schmidt, "A Rural Phenomenon: Lying-in-the-Road Deaths," The New York Times, June 30, 1986. / 3 The number of Americans of driving age: here and elsewhere in this book, population statistics and characteristics are generally drawn from U.S. Census Bureau data. / 3 "Friends Don't Let Friends...": By total happenstance, we recently met one of the creators of the original slogan "Friends Don't Let Friends Drive Drunk." Her name is Susan Wershba Zerin. In the early 1980s, she worked at the Leber Katz Partners ad agency in New York and was the account manager on a pro bono anti-drunk-driving campaign for the U.S. Department of Transportation. "Elizabeth Dole, the secretary of transportation, was our key contact," she recalls. The phrase "Friends Don't Let Friends Drive Drunk" was written as the campaign's internal strategic statement, but it proved so memorable in-house that it was adopted as the campaign's tagline.

THE UNLIKELY SAVIOR OF INDIAN WOMEN: This section draws substantially from Robert Jensen and Emily Oster, "The Power of TV: Cable Television and Women's Status in India," Quarterly Journal of Economics, forthcoming. For more on living standards in India, see the United Nations Human Development Report for India; "National Family Health Survey (NFHS-3), 200506, India," The International Inst.i.tute for Population Sciences and Macro Intl.; and "India Corruption Study 2005," Center for Media Studies, Transparency International, India. / 4 On the unwantedness of girls in India and the use of ultrasounds to identify them for abortion, see NFHS-3 report; and Peter Wonacott, "India's Skewed s.e.x Ratio Puts GE Sales in Spotlight," The Wall Street Journal, April 19, 2007; and Neil Samson Katz and Marisa Sherry, "India: The Missing Girls," Frontline, April 26, 2007. / 4 For more on the persistence of dowry in India, see Siwan Anderson, "Why Dowry Payments Declined with Modernization in Europe but Are Rising in India," Journal of Political Economy 111, no. 2 (April 2003); Sharda Srinivasan and Arjun S. Bedi, "Domestic Violence and Dowry: Evidence from a South Indian Village," World Development 35, no. 5 (2007); and Amelia Gentleman, "Indian Brides Pay a High Price," The International Herald Tribune, October 22, 2006. / 4 The Smile Train story comes from author interviews with Brian Mullaney of Smile Train; see also Stephen J. Dubner and Steven D. Levitt, "Bottom-Line Philanthropy," The New York Times Magazine, March 9, 2008. / 4 For more on the "missing women" of India, see Amartya Sen, "More Than 100 Million Women Are Missing," The New York Review of Books, December 20, 1990; Stephan Klasen and Claudia Wink, published in K. Basu and R. Kanbur (eds.), Social Welfare, Moral Philosophy and Development: Essays in Honour of Amartya Sen's Seventy-Fifth Birthday (Oxford University Press, 2008); and Swami Agnivesh, Rama Mani, and Angelika Koster-Lossack, "Missing: 50 Million Indian Girls," The New York Times, November 25, 2005. See also Stephen J. Dubner and Steven D. Levitt, "The Search for 100 Million Missing Women," Slate, May 24, 2005, which reported on Emily Oster's finding of a connection between missing women and hepat.i.tis B; but see also Steven D. Levitt, "An Academic Does the Right Thing," Freakonomics blog, The New York Times, May 22, 2008, in which the hepat.i.tis conclusion was found to be faulty. / 5 Son worship in China: see Therese Hesketh and Zhu Wei Xing, "Abnormal s.e.x Ratios in Human Populations: Causes and Consequences," Proceedings of the National Academy of Sciences, September 5, 2006; and Sharon LaFraniere, "Chinese Bias for Baby Boys Creates a Gap of 32 Million," The New York Times, April 10, 2009. / 5 Information about bride burning, wife beating, and other domestic atrocities can be found in Virendra k.u.mar, Sarita Kanth, "Bride Burning," The Lancet 364, supp. 1 (December 18, 2004); B. R. Sharma, "Social Etiology of Violence Against Women in India," Social Science Journal 42, no. 3 (2005); "India HIV and AIDS Statistics," AVERT, available at www.avert.org/indiaaids.htm; and Kounteya Sinha, "Many Women Justify Wife Beating," The Times of India, October 12, 2007. / 5 "The condom is not optimized for India": see Rohit Sharma, "Project Launched in India to Measure Size of Men's p.e.n.i.ses," British Medical Journal, October 13, 2001; Damian Grammaticus, "Condoms 'Too Big' for Indian Men," BBC News, December 8, 2006; and Madhavi Rajadhyaksha, "Indian Men Don't Measure Up," The Times of India, December 8, 2006. / 5 Apni Beti, Apna Dhan is described in Fahmida Jabeen and Ravi Karkara, "Government Support to Parenting in Bangladesh and India," Save the Children, December 2005.

DROWNING IN HORSE MANURE: See Joel Tarr and Clay McShane, "The Centrality of the Horse to the Nineteenth-Century American City," in The Making of Urban America, ed. Raymond Mohl (Rowman & Littlefield, 1997); Eric Morris, "From Horse Power to Horsepower," Access, no. 30, Spring 2007; Ann Norton Greene, Horses at Work: Harnessing Power in Industrial America (Harvard University Press, 2008). Also based on author interviews with Morris, McShane, and David Rosner, Ronald H. Lauterstein Professor of Sociomedical Sciences at Columbia University. / 11 Climate change will "destroy planet Earth as we know it": see Martin Weitzman, "On Modeling and Interpreting the Economics of Catastrophic Climate Change," The Review of Economics and Statistics 91, no. 1 (February 2009). / 12 The case of the stolen horse manure is recounted in two Boston Globe articles by Kay Lazar: "It's Not a Dung Deal," June 26, 2005; and "Economics Professor Set to Pay for Manure," August 2, 2005.

WHAT IS "FREAKONOMICS," ANYWAY? Gary Becker, the original freakonomist, has written many books, papers, and articles that should be widely read, including The Economic Approach to Human Behavior, A Treatise on the Human Family, and Human Capital. See also his n.o.bel Prize acceptance speech, "The Economic Way of Looking at Life," n.o.bel Lecture, University of Chicago, December 9, 1992; and The n.o.bel Prizes/Les Prix n.o.bel 1992: n.o.bel Prizes, Presentations, Biographies, and Lectures, ed. Tore Frangsmyr (The n.o.bel Foundation, 1993). / 13 "Our job in this book is to come up with such questions": as the renowned statistician John Tukey once reportedly said, "An approximate answer to the right question is worth a great deal more than a precise answer to the wrong question." / 13 One breast, one t.e.s.t.i.c.l.e: for this thought, a hat tip to the futurist Watts Wacker.

SHARK-ATTACK HYSTERIA: The Time magazine cover package appeared on July 30, 2001, and included Timothy Roche, "Saving Jessie Arbogast." / 15 The definitive source for shark attack statistics is the International Shark Attack File, compiled by the Florida Museum of Natural History at the University of Florida. / 15 Elephant deaths: see People and Wildlife, Conflict or Co-existence, ed. Rosie Woodroffe, Simon Thirgood, and Alan Rabinowitz (Cambridge University Press, 2005). For more on elephants attacking humans, see Charles Siebert, "An Elephant Crackup?" The New York Times Magazine, October 8, 2006.

CHAPTER 1: HOW IS A STREET PROSt.i.tUTE LIKE A DEPARTMENT-STORE SANTA?

MEET LASHEENA: She is one of the many street prost.i.tutes who partic.i.p.ated in Sudhir Venkatesh's fieldwork, summarized in much further detail later in the chapter and contained in Steven D. Levitt and Sudhir Alladi Venkatesh, "An Empirical a.n.a.lysis of Street-Level Prost.i.tution," working paper.

HARD TO BE A WOMAN: For historic life expectancy, see Vern Bullough and Cameron Campbell, "Female Longevity and Diet in the Middle Ages," Speculum 55, no. 2 (April 1980). / 20 Executed as witches: see Emily Oster, "Witchcraft, Weather and Economic Growth in Renaissance Europe," Journal of Economic Perspectives 18, no. 1 (Winter 2004). / 20 Breast ironing: see Randy Joe Sa'ah, "Cameroon Girls Battle 'Breast Ironing,'" BBC News, June 23, 2006; as many as 26 percent of Cameroonian girls undergo the procedure, often by their mothers, upon reaching p.u.b.erty. / 20 The plight of Chinese women: see the U.S. State Department's "2007 Country Reports on Human Rights Practices" for long-term consequences of foot binding, see Steven c.u.mmings, Xu Ling, and Katie Stone, "Consequences of Foot Binding Among Older Women in Beijing, China," American Journal of Public Health 87, no. 10 (1997).