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

by Kenrick, Douglas T.

  Would human (and monkey) brains come prewired to be loss averse if this bias led our ancestors to persistently make bad decisions? Probably not. It makes more sense that our brain arrives with a built-in bias because this bias has historically led to decisions that enhance fitness. Natural selection is a pretty efficient process, so if a behavior is found widely in humans and other species, it’s a better starting guess to presume it is adaptive rather than to assume it’s merely dumb.

  When considered in terms of evolutionary success, many of the seemingly irrational choices that people make do not seem so foolish after all. Most animals, including our ancestors and modern-day capuchin monkeys, lived very close to the margin of survival. Paleontologists who study early human civilizations have uncovered evidence that our ancestors faced frequent periods of drought and freezing. When you are living on the verge of starvation, a slight downturn in your food reserves makes a lot more difference than a slight upturn. Anthropologists who study people still living in hunter-gatherer and simple horticultural societies have discovered that they regularly make choices designed to produce not the best opportunity for obtaining a hyperabundant supply of food but, instead, the least danger of ending up with an insufficient supply. In other words, people everywhere have a strong motivation to avoid falling below the level that will feed themselves and their families. If our ancestors hadn’t agonized over losses and instead had taken too many chances in going after the big gains, they’d have been more likely to lose out and never become anyone’s ancestor.

  Although we may not be living under the same conditions as our Ice Age progenitors, we did inherit our brains from them. So to understand how we behave in the modern world, it is essential to look at the broader picture. Evolutionary psychologists try to pull together the different threads, to interweave the diverse findings from psychology and economics with those from anthropology and biology. When we look at the deeper logic of decisions across the entire animal kingdom, it becomes clear that decision making in all critters, including us, is geared to promote deep-seated evolutionary goals. This is important because it suggests that many of our decision biases, errors, and misjudgments might not be design flaws; instead, they may be design features.

  PROXIMATE VERSUS ULTIMATE REASONS FOR BEHAVIOR

  Imagine you have a friend who just spent $5 on a triple-chocolate fudge brownie, and you want to know the reason behind her purchase. So you ask her, “Why did you buy that?” She might simply respond, “I was hungry.” If she were feeling more analytical, she might mention that she loves the taste of chocolate and couldn’t resist the delectable scent of a freshly baked brownie.

  Your friend’s explanations for her behavior refer to something biologists call proximate causes. The word “proximate” here is related to the word “proximity.” These causes point to relatively up-close and immediately present influences—to what I am presently feeling or thinking, for example.

  Proximate causes are important, but they tell only the surface part of the story. They don’t address the deeper question: Why do brownies taste good in the first place? This deeper inquiry seeks what biologists call an ultimate cause. Ultimate explanations go below the surface, focusing not on the immediate triggers of a behavior but on their evolutionary function. They ask what purpose a certain tendency would have served for our ancestors. In the brownie case, we humans have brains that light up whenever we see, smell, or eat foods that are rich in sugars and fats. These brownie-appreciation mechanisms exist because an attraction to calorie-dense foods helped our ancestors store energy and survive in an environment in which nutritious foods were often scarce. This is the ultimate reason why most humans are attracted more to fatty and sugary brownies than to much healthier, low-calorie, fat-free kale. Whereas the proximate reason your friend shelled out $5 for a triple-chocolate fudge brownie may be that she liked its pleasant aroma, the ultimate reason is that a preference for sugary and fatty foods helped solve the critical evolutionary challenge of survival.

  Economists and psychologists of all stripes have typically been concerned only with proximate reasons for human behavior. At the proximate level, people behave one way rather than another because they want to feel good. People strive to experience pleasure, happiness, or satisfaction and to avoid pain, sadness, or frustration. Economists characterize all proximate goals as providing “utility.” If you ask an economist why a person has done something, the answer is always utility. For example, when I decide to blow $200 for dinner at Café Sydney in Australia, I have concluded that the utility I’ll get from the stunning views of Sydney Harbor, the artfully presented and delicately spiced fusion cuisine, and the fine bottle of Hunter Valley Semillon is greater than the utility I’d get from spending $10 twenty times at McDonald’s.

  If you delve into the massive scientific literature on decision making, you will discover mostly proximate explanations for human choices. But the entire other half of the story—the ultimate reasons for behavior—is conspicuously missing.

  It can be easy to overlook the ultimate reasons for behavior. They are often difficult to see, especially if you don’t even realize there is something more going on beneath the surface. In some cases, the link between proximate and ultimate reasons for behavior is readily apparent. In the case of the brownie, a proximate explanation, such as “I was starving,” connects obviously to the ultimate goal of obtaining calories to survive, and the conscious link is not hard to make. But often the links between proximate and ultimate reasons are not so clear. Consider the question of why birds migrate each year. The proximate reason is because days get shorter; day length is the immediate cue triggering the bird’s motivation to begin its journey. But the ultimate reason for bird migration has nothing to do with day length. Instead, it has to do with the fact that the best food and mating sites change with the seasons.

  When an oriole decides to make his annual trek from Baltimore, Maryland, to Bogota, Colombia, the bird does not need to be aware of the connections between day length, seasons, survival, and mating. Likewise, it’s a safe bet that we bird-watching hominids are usually unaware of most of the connections between the proximate triggers for our decisions and the ultimate evolutionary reasons behind them. To make decisions right here and now, you don’t need to understand how your choices connect to your ancestors’ success, any more than you need to know the history of the automobile or the principles of the combustion engine to turn the ignition key and drive to the supermarket. But just because you’re not always aware of the ultimate reasons for your behavior, that doesn’t mean they’re not influencing your choices at a subconscious level.

  THE SUBCONSCIOUS INFLUENCE OF THE OVULATORY CYCLE

  Imagine you’re a woman shopping online for clothing. Do you think you will buy different outfits on days when your body’s physiology makes you more likely to become pregnant?

  A woman’s ability to become pregnant depends on her menstrual cycle, which in humans typically spans about four weeks. A woman can become pregnant during roughly one week of the cycle, known as the ovulatory phase. Whereas female chimpanzees advertise their ovulatory phase with a bright red swollen rump, for humans the signals are not so obvious. Without specific education or equipment, most college-age women do not even know when they themselves are ovulating. But if a woman is unaware that she is ovulating, does that mean it can’t influence her behavior?

  To dig a little deeper, marketing professor Kristina Durante and her research team recruited women who were not on hormonal contraception. When the women arrived for the study, they were given a urine test, which involved a trip to the restroom to pee on a stick. Although the women were told this test was a measure of their general health, the actual purpose was to determine whether they were experiencing the hormonal surge associated with ovulation. Ovulating and nonovulating women were then sent on an online shopping spree—to a website designed to look like The Gap or Old Navy. The virtual store had over one hundred clothing items and fashion accessories, includ
ing pants, skirts, shirts, shoes, handbags, and purses. But the products were strategically preselected. Half the items were sexier, flashier, and more alluring, while the other half were more conservative and demure. Even though none of the women in the study knew whether or not they were ovulating, those in the fertile phase of their cycle chose sexier and more revealing clothing—shorter skirts, higher heels, and sheerer blouses that revealed a lot of skin.

  It turns out that ovulation alters women’s behavior even when they aren’t wearing any clothing at all. In another study, Geoffrey Miller, Josh Tybur, and Brent Jordan recruited a rather unusual team of research assistants—eighteen women who made their living as professional lap dancers in “gentlemen’s clubs.” The women recorded their tips over a sixty-day period, during which the researchers monitored each woman’s phase in her cycle. When the dancers were least fertile, they made an average of $185 per five-hour shift. But when they were ovulating, they made almost twice as much: $335. The researchers speculated that ovulation subconsciously led the women to act sexier, leading an invisible change in the women’s hormonal condition to have a very visible economic effect.

  If you were to ask a woman who is currently ovulating why she chooses to buy a sexy dress, she might offer a proximate explanation, such as “I’m feeling adventurous” or “I’m in a party mood today.” Such explanations are useful for understanding what’s going on at the surface, but they say nothing about why ovulation leads women to feel more adventurous in the first place. At a deeper, ultimate level, the reason why ovulation alters women’s behavior goes well beyond their current mood.

  Throughout evolutionary history, women’s behavior has had the largest reproductive consequences during the brief monthly window when they are ovulating, and can therefore become pregnant. In other mammals, ovulation is known to alter female behavior in ways to maximize reproductive opportunities during the fertile phase (think about those red rumps on our chimpanzee cousins). An ovulating woman’s hormones appear to do likewise, altering her decisions to maximize her mating opportunities at the precise time of the month when doing so would have mattered most to her ancestors.

  The proximate reason why ovulation leads a woman to dress and behave in a more alluring manner might be that she feels more adventurous at this time. But the ultimate reason is that ovulation promotes behavior designed to make women more appealing to the opposite sex. This suggests that women feel more adventurous and flirtatious during the particular time when pregnancy is most likely because such feelings would have produced behavior that best served their ancestors’ reproductive interests. Whether we’re trying to figure out why hungry people eat brownies or why ovulating women buy sexy dresses, it is useful to know the ultimate, not just the proximate, reasons for these behaviors.

  An ultimate explanation does not contradict a proximate explanation. It would be senseless to argue whether a person bought a brownie because she was hungry (a proximate reason) or because sugary and fatty foods helped her ancestors solve the evolutionary challenge of survival (an ultimate reason). Instead, the two levels of explanation complement one another. A proximate explanation explains what’s happening on the surface; an ultimate explanation explains what’s going on at a deeper, evolutionary level.

  Why should you care about the ultimate causes of people’s choices? For one thing, proximate explanations by themselves provide an incomplete and often unsatisfying understanding of human behavior. For example, an economist might observe a number of ovulating women buying sexy dresses and infer that sexy outfits must be especially desirable to women at that particular phase of the menstrual cycle. But this fact alone tells us nothing about why. In fact, most traditional scientists would have had no reason to even begin investigating whether women’s purchasing decisions change depending on their ovulatory cycle. And even if they stumbled upon the relationship, they might conclude that acting sexy during ovulation is irrational, since at the surface level modern female shoppers or exotic dancers may have absolutely no conscious interest in getting pregnant. To fully understand what’s actually going on, we need to go below the surface.

  Looking below the surface—at the ultimate reasons underlying our behaviors—provides valuable insight into decisions that might otherwise seem strange. Behavioral economists, for instance, have identified myriad decision errors, biases, and distortions. But they have simply provided a laundry list of blunders without offering a theory of the underlying causes for why people make these mistakes. Evolutionary psychology, on the other hand, provides a theory of mistakes. As we describe in this book, this adaptive theory of mistakes not only helps us appreciate the hidden wisdom of our otherwise senseless decisions but allows us to predict in advance what particular mistakes people will make—and when.

  THE KENNEDYS AND THE BIOLOGY OF RISK

  Let’s reconsider the curse of the Kennedys in light of the distinction between surface-level explanations and their deeper evolutionary causes. On the surface, Joe Kennedy’s descendants made a lot of choices that seemed rather foolish. The willingness to make hazardous choices started with Joe Kennedy himself. He got to be the youngest bank president by going way out on a limb—he borrowed lots of money and went head-to-head with Boston’s powerful financiers in a deal that could have turned out quite badly. In fact, not all of Joe Kennedy’s risks paid off. A few years before pulling off his famous $650,000 Wall Street win, he lost most of his assets by following a bad tip on a stock that later plunged to half its value. And while he was a student at Harvard, he took other risks as well. Despite the antialcohol laws, Kennedy supplied plentiful booze at parties. And his liquor business continued to flow during Prohibition, leading later commentators to speculate that he had some shady connections with the underworld. (Mobster Frank Costello claimed to have done business with Joe Kennedy before the Irishman moved on to more legitimate enterprises.)

  Joe Kennedy took chances in the sexual department as well. He had affairs with many women, not just Hollywood starlet Gloria Swanson, despite his prominence in Boston’s Roman Catholic establishment. Joe’s descendants were notorious for risky decisions when it came to women and sex. JFK infamously used his Secret Service agents to cover for him when he snuck beautiful women into the White House. And to make bad judgment worse, one of the president’s mistresses was a friend of Mafia don Sam Giancana—a fact Republicans later leaked to the press. Later, Joe’s grandson Michael Kennedy narrowly avoided going to jail for statutory rape after an affair with a teenage babysitter, and another Kennedy grandchild, William Kennedy Smith, was accused of sexual assault by several different women and prosecuted for rape in one case. And what was Teddy, a married man, doing in that car with Mary Jo Kopechne in the first place?

  What does all this risky behavior have to do with evolutionary biology? A lot, it turns out. Beneath the surface of seemingly ill-advised choices is a deeper link between men’s risk taking and reproductive success. Women in societies all around the world are attracted to ambitious men who are willing to take risks to become successful (we’ll talk more about women’s psychology in Chapter 8, “Sexual Economics: His and Hers”).

  This doesn’t mean that a man’s risky choice will always lead to reproductive success. Risk, after all, is inherently risky. But the link between risk and mating does suggest that men are not likely to take risks haphazardly. Instead, men should be prone to making riskier choices specifically when their behavior could lead to a reproductive opportunity. To see how this works, let’s go Down Under.

  At a skateboard park in Queensland, Australia, psychologists Richard Ronay and William von Hippel offered ninety-six young male skaters $20 to perform two tricks on their speedy little land-surfing devices. The researchers asked skaters to choose one easy trick and a more difficult stunt they were working on but could only complete successfully about half the time. A male researcher filmed the skateboarders as they practiced their two tricks. Midway through filming, though, a highly attractive eighteen-year-old female strutted on
to the scene. To verify that young blokes found her good-looking, the researchers asked twenty other guys to rate her attractiveness. Not only did she score as a knockout, but the ratings were, as the researchers noted, “corroborated by many informal comments and phone number requests from the skateboarders.”

  With the attractive young woman looking on, each skateboarder demonstrated his tricks a few more times, then donated a sample of saliva to the researchers, who later analyzed it for the amount of the hormone testosterone.

  The researchers found that the beautiful woman caused the young skaters to throw caution to the wind. Taking more chances led to a lot more crash landings, but it also led to more successes on the difficult tricks—the kind of daring stunts that a young woman who enjoys the punk musical stylings of the Dead Kennedys might find impressive. But this boost in riskiness was accompanied by two additional findings that reveal something deeper about the evolutionary biology of risk.

  First, the guys’ testosterone levels automatically shot up when the beautiful woman was watching. Having more testosterone flowing through their veins tends to inspire men to move faster and more recklessly. In fact, the boost in risk taking was found primarily among those fellows whose testosterone levels zoomed up the most.

  Second, the researchers gave the men a test tapping the functioning of the ventral medial prefrontal cortex, an area of the brain that cranks into high gear when we need to assess rewards and punishments. When the beautiful woman was watching, guys did worse on the test, suggesting that boosts in testosterone may have shut down this brain area, normally involved in making careful judgments. These findings make evolutionary sense to the extent that successfully showing off to a beautiful woman enhances a man’s chances of attracting her as a mate. To show off, though, a bloke needs to be willing to throw caution to the wind—to take his foot off the brakes and hit the gas—and take some otherwise foolish risks.