The Rational Animal: How Evolution Made Us Smarter Than We Think

by Kenrick, Douglas T.

  WEDDING BONDS: THE MATE-RETENTION GAME

  A while back, one of our wives took a course in which the professor recommended a rational economic approach to resolving conflicts in relationships. The idea was that one spouse should provide rewards to the partner in exchange for getting something he or she desired in return. For example, if the man finds sex more rewarding than does the woman, but she likes to eat in nice restaurants more than he does, the wife could simply make sexual favors contingent on the man shelling out for an upscale meal. The professor’s advice followed directly from the model of rational economics. But although this Wall Street approach might make sense in an interaction between a prostitute and a john, we actually don’t recommend that you try it at home.

  Exchanges between long-term romantic partners are not like those between customers and shopkeepers, but they’re also not quite like those during the initial courtship. From an evolutionary perspective, human males and females form partnerships (such as marriage) because those partnerships have historically benefitted their children. Because those children share their parents’ genes, mom’s and dad’s genetic interests become a bit sibling-like. But despite their common genetic incentives, spouses’ interests are not identical to those between brothers and sisters. When our sibling goes on a date with a great new romantic partner, we are likely to count this as a benefit; if our spouse became involved with a new lover, on the other hand, we’d likely count this as a substantial loss and sufficient grounds to terminate the relationship completely.

  Divorces in particular highlight that blood is thicker than wedding wine. When romantic pairs split up, formerly loving couples who once comfortably shared million-dollar homes begin to fight bitterly over every compact disc, fork, spoon, and folding chair. Many families continue to support and care about their prodigal sons, but there’s typically not much love lost between former spouses, and any exchanges of resources that do occur often involve both sides feeling cheated.

  The rules for marriage partners also differ in another way from the initial rules for dating partners. Although women tend to be choosier than men when it comes to short-term relationships (recall women’s higher standards for a one-night stand), men and women are more alike than different when it comes to marriage partners. Men looking for a marriage partner want every bit as many IQ points as women do. This makes sense in terms of human evolution. It is possible for a man to have offspring in the typical mammalian style—with very little investment (some of our male ancestors benefitted greatly from having lots of one-night stands). But our species differs from 95 percent of other mammals in that human males typically stay around and contribute resources after their young are born. Sometimes men even stay around for the rest of their lives, faithfully bringing home their paychecks, fixing leaks in the roof, and taking out the garbage. Thus, when it comes to getting married, as compared to having an affair, men are in for a much higher commitment of resources. Hence, men up their standards considerably for marriage partners.

  JEALOUSY: HIS AND HERS

  Although men and women are more similar than different when it comes to their standards for marriage partners, wedding bonds and parenthood don’t completely erase all sex differences. Even after a couple has a child, there remains a nagging biological wrinkle called paternal uncertainty. Barring one of those movie-plot exchanges of babies in the nursery, a woman has no doubts about whether a given child is hers or not. For a man, however, there is never complete certainty. Even if his wife has been completely faithful, as in the vast majority of cases, the man does not know this for certain unless he can be sure he was with her every minute of that fateful ovulatory cycle nine months ago. Studies show that somewhere between 3 and 10 percent of children are not the biological descendants of the man listed as the father on their birth certificate. To add legal insult to this genetic injury, a divorced man is, in many jurisdictions, required to continue making child-support payments, even if DNA tests establish that he is not the biological father of a child born during his marriage.

  Paternal uncertainty leads to an interesting sex difference in the triggers for jealousy. Imagine that the person with whom you’ve been seriously involved has become interested in someone else. What would make you more upset: (1) your partner falls in love with and forms a deep emotional attachment to the other person, or (2) your partner has sexual intercourse one night with that other person?

  When evolutionary psychologist David Buss and his colleagues asked this question, they found that men and women had very different reactions. Approximately 80 percent of women said they would be more upset to discover that their man had formed an emotional attachment to another woman. For men, the findings were reversed. Although guys did not find it especially pleasant to think about their woman forming an emotional attachment, the majority of men said they would be even more distressed to discover a sexual infidelity. Other researchers have found the same sex difference in Korea, Japan, Germany, the Netherlands, and Sweden. In fact, even though men are more likely to be unfaithful in a relationship, it is a woman’s sexual infidelity that is more likely to lead to divorce. And it gets a lot more serious than that—around the world, jealousy is a common cause of homicide, with men being more than four times as likely to kill over jealousy.

  On the other side of the equation, although a woman does not have to worry about unintentionally raising someone else’s child, she does stand to lose her husband’s resource contributions if he falls in love with another woman. Given that the average man will jump into bed with a strange woman who approaches him on a college campus, a wife may appreciate that her partner’s sexual tryst does not necessarily mean he’s deeply committed to the other woman. Although she will likely be far from thrilled by her husband’s philandering, she may have considerably more concerns about his emotional attachments. The emotional attachment is a stronger indicator that he might divert resources from his current family to the other woman. The psychology of men’s and women’s jealousy seems to have been shaped by subtle biological differences in reproduction. And as we discuss next, those subtle differences can even affect your credit score.

  SEXUAL SUPPLY AND DEMAND

  Macon and Columbus, Georgia, are two cities less than a hundred miles apart. They share a similar history and economic climate. Yet the residents of the two cities have drastically different spending habits. The good folks down in Columbus carry massive credit card debt, averaging $3,479 more per person than their fellow Georgians over in Macon. Why the big difference? An important clue comes from a second difference between the two cities. Whereas in fiscally responsible Macon there are only 0.78 single men for every woman, in debt-strapped Columbus there are 1.18 single men for every woman.

  In their classic book Too Many Women?, Marcia Guttentag and Paul Secord argue that fluctuations in sex ratios—the ratio of adult men to women in a particular geographical location—have dramatic effects on sexual behaviors. When there are more women, as happens during and after major wars, there is more promiscuity, people get married later, and more children are born out of wedlock. When there are more men, on the other hand, guys start getting more committal, marrying earlier, running around less, and investing more in their families.

  All this makes sense in terms of basic mating economics. When women are scarce, they call the shots, demanding that men commit more time and resources to them alone. But when men are scarce and have easy access to multiple women, guys are less willing to commit to any single woman, and women must consequently lower their demands. Guttentag and Secord even argue that shifting sex ratios in the population had a lot to do with the sexual revolution and “free love” ethos of the 1960s and 1970s in the United States. During this time of sexual experimentation, there were more women than men.

  If you’ve ever seen the reality television programs The Bachelor or The Bachelorette, you’ve observed the behavioral consequences of an imbalanced sex ratio. On The Bachelor, where twenty-five women spend several weeks vying for o
ne man’s hand in marriage, the women become catty and malicious toward each other, while growing more promiscuous and more tolerant of their man’s promiscuity. The ladies are visibly annoyed as they watch their “boyfriend” make out with other women and even share an overnight “fantasy suite” with three different ladies on consecutive nights. But when the sex ratio dictates that the man can call the shots, there is little the women can do.

  In contrast, on The Bachelorette, where twenty-five men vie to propose to one lucky lady, the men are chivalrous and refined in front of their potential girlfriend, telling her how much they want to settle down and start a family. Meanwhile the boys brutishly get into fistfights with each other when she’s not around. The sex ratio’s effect on violence is no laughing matter. In India, sex ratios vary greatly among different regions, and a 1 percent change in sex ratio is associated with a 5 percent change in the murder rate! Homicides increase dramatically when women are scarce.

  How does all of this relate to credit card debt in Georgia? Because there are more available guys in Columbus, each guy has to compete harder for one of those scarce women. One way to do that is to spend money, buy flashier cars, and take dates out to more expensive restaurants. When Vlad and his team calculated sex ratios in 134 cities across America, they found a striking relationship between the sex ratio, the number of credit cards people owned, and the average debt a person had. The fewer the women in a city, the higher the debt and the more credit cards people had.

  Although the results were consistent with mating economics, it was not certain whether it was men or women who were spending more. So the team moved to the laboratory to conduct more rigorous studies. College students were shown photographs of crowds of other students. Some saw photographs in which the majority of people were men; others saw photos in which the majority were women. Then people in the study were presented with an actual opportunity to get $20 tomorrow or $35 in a month. Sex ratio did not affect women’s choices, but men who had seen a lone woman surrounded by other men became more impulsive and chose immediate payoffs. Never mind that the more delayed option presented a much better investment opportunity (you try to find an investment that yields 75 percent interest per month). When women were scarce, men wanted money now.

  In another study, people read a news article from the Chicago Tribune describing the local population as either having more single men or more single women. One headline read, for example, “Fewer Women for Every Man.” Other people read a story that reversed the headline to say there were fewer men for every woman. After reading the article, people indicated how much money they would save each month from a paycheck, as well as how much money they would borrow on a credit card for immediate expenditures.

  When women were scarce, men cut their savings by 42 percent. If the men felt that they still didn’t have enough money for things they needed now, they increased their credit card debt by 84 percent. And where did the money go? To the women, of course. When women were scarce, men paid more for Valentine’s Day gifts and more for engagement rings ($278 more, in fact). On the other side of the equation, women who felt they were scarcer were in fact harder to impress. After they’d just read that there were lots of single men in the area, they fully expected those hopeful fellows to spend more on gifts and engagement rings.

  The financial consequences of sex ratio are on full display in Las Vegas—a city with 1.16 men for every woman, one of the most male-skewed cities in America. Las Vegas often lures men (and their wallets) with the promise of an abundance of females, but in reality casino floors are flush with many more men than women. And when a man in a casino is surrounded by many other men and only a few ladies, he is most likely to lay down the big bets from which casinos profit.

  The effects of sex ratios extend beyond the casino floor or even the United States. China, for example, currently has a surplus of 40 million extra single men. As a consequence, the practice of bride price has been returning to China in full force. Some areas have seen a fourfold increase in bride price in the last decade, and half of the men in the countryside can no longer even afford a bride, which sometimes costs as much as three hundred cows. Men from Asian countries with a shortage of women are now paying large sums of money for wives from other countries such as Vietnam. In turn, the men in Vietnam are beginning to feel the need for more resources, just like the good ole boys down in Columbus, Georgia.

  BLOKES, SHEILAS, AND WALLETS

  Maybe you’ve never bought a spouse for £2,000 or engaged the services of an “elite social introduction service” for $31,000 a night. But it’s nearly certain that your decisions have been affected by whether your mating subself is of the his or hers type.

  If you’re a typical woman, you have probably spent more dollars than you’d care to count on makeup, hair products, and stylish clothes, all designed to make you appear more like the prototypical fertile member of our species. And without your even being aware of it, your spending patterns have likely been influenced by your own ovulatory cycles and by the economy’s financial cycles (as when women boost their spending on beauty products during an economic decline).

  If you’re a typical man, you have spent countless dollars buying drinks, flowers, and dinners to woo women. If you haven’t conspicuously thrown away money on flashy cars, expensive watches, and drinks for the house, then maybe you’ve quietly purchased tasteful gifts for that special woman to whom you want to prove your commitment. Your spending patterns have been influenced not only by daily fluctuations in your testosterone levels but also by the local ratio of blokes to sheilas. And although much of this has been happening outside your awareness, it has reflected the operation of a brain designed to make these decisions in a way that is, ultimately, deeply rational.

  OUR TOUR OF the rational animal’s habitat has so far included visits with a wide cast of colorful characters, including the studded rocker Elvis Presley, the fast-spending rapper MC Hammer, the technological visionary Steve Jobs, and a high-priced Las Vegas lap dancer named April. Our journey in search of humankind’s deeper nature has taken us around the world, from Amazonia to Zambia, with stops in Macon, Georgia, and a gentleman’s club in Albuquerque, New Mexico. Next we bring it all back home, revisiting each of the subselves inside your head and paying special attention to the various parasites who are trying to sneak in there every day. As we’ll see, these parasites try to turn your own subselves against you, exploiting your otherwise smart evolutionary biases to sell you products, solicit your contributions, and otherwise take you for a ride.

  9

  Deep Rationality Parasites

  THE EUROPEAN CUCKOO, whose distinctive call is immortalized in the sound of the cuckoo clock, would not qualify for a good-parenting award. Whereas most birds sit patiently on their eggs to keep them warm and protected, the cuckoo simply deposits its precious offspring-to-be in a total stranger’s nest. To trick a bird of another species into caring for its young, the cuckoo first slyly removes an egg from the unsuspecting host’s nest, replacing it with one of its own, which often closely mimics the pilfered egg’s appearance.

  But the scam doesn’t end there. As soon as the young cuckoo hatches, its first act is to dispose of any other eggs in the nest, leaving itself as the sole occupant. With the disappearance of their rightful young, the foster parents are now free to devote all their care and attention to their new only child. The hoodwinked parents, commonly a pair of tiny reed warblers, don’t appear to notice they are rearing an impostor, which quickly grows to twice the size of its providers. Meanwhile, loving mommy and daddy work like Sisyphus around the clock to keep up with the voracious appetite of the gigantic young cuckoo.

  The cuckoo is an especially nefarious social parasite, deviously exploiting the adaptive tendencies of its fellow birds for its own gain. But parasitism isn’t a rarity in the animal kingdom. Virtually every successful organism attracts the company of leeches, moochers, stowaways, and manipulators seeking to take advantage of its evolutionary success. Hu
mans are likewise not exempt from parasites, and our free riders range from microscopic one-celled organisms to other human beings.

  Fellow-person parasites often take the form of the various profiteers lurking in our midst, some of whom are adorned in religious robes, political sashes, or freshly pressed business suits. But rather than hiding eggs in our nests, these miscreants seek to swipe our nest eggs.

  Consider Bernard Madoff, the former chairman of the NASDAQ stock exchange, who orchestrated the largest financial fraud in US history, bilking investors out of $18 billion (not to be confused with $18 million, which, though still a fortune, would be a thousand times less). Just as cuckoos exploit the adaptive instincts of their fellow birds, Madoff exploited those of his fellow man. In the same way a cuckoo tricks unsuspecting birds by producing eggs that resemble those laid by their victims, Madoff preyed on people with whom he shared common bonds of affinity and religion. A well-respected member of a tightknit Jewish community, Madoff targeted fellow in-group members such as Steven Spielberg, Elie Wiesel, Mort Zuckerman, and Frank Lautenberg, as well as Yeshiva University and the Women’s Zionist Organization of America. Operating as an insider, Madoff approached individuals of his faith with special offers. Although people are naturally suspicious of anything that sounds too good to be true, a common heritage with Madoff provided a reason to trust that he was offering an inside deal. This sense of tribal affinity also made it difficult to ask hard questions. Interrogating a fellow member of the inner circle for hard information is like demanding receipts from your beloved Aunt Mildred—you just don’t question family. But rather than helping members of the inner circle, who were told their investments were worth $65 billion, old Bernie tricked them into funding the escapades of the Madoff clan.