The following is an excerpt from Jonathan Rottenberg's new book, The Depths: The Evolutionary Origins of the Depression Epidemic (Basic Books, a member of the Perseus Books Group, 2014). Reprinted with permission of the publisher. All rights reserved.

The puzzling reality is that human depression is increasing in an era when environmental conditions are relatively benign. The average citizen in Western society now lives longer, is less likely to starve, and enjoys considerably greater wealth than his sixteenth-century counterpart. Presumably these objective conditions for survival and reproduction would cause depression rates to fall, not rise to nearly one in five citizens. This environment-depression disconnect seems less strange when we appreciate that there are additional human-specific routes into depression. Homo sapiens has the dubious distinction of being a species that can become depressed without a major environmental insult.

There is no scientific consensus about why human depression rates are rising in the industrialized world, but several compelling possibilities exist. Their common thread is our species’ unusual relationship with mood and the doors it opens for unique routes into depression. A chimpanzee is capable of feeling bad, but only a human being can feel bad about feeling bad. Former tennis great Cliff Richey, in his memoir “Acing Depression,” described how he became engulfed by low mood: “One of the horrible things about depression—in addition to the foul, odorous, sick, deathly mood you’re in—is that you’re now spending so much of your time, almost all of it, just trying to fix yourself. You’re consumed by, ‘How can I fix this horrible thing?’”

Humans have a host of unique thoughts and reactions to low mood, many of which are highly cognitive. Only a human can keep a mood diary or write a book about depression. We often think of what’s uniquely human as uniquely better. Surely pride may be a reasonable emotion for the species that harnessed fire and put a man on the moon. It’s easy to see traits such as advanced language, the ability to be self-aware, and participation in a rich shared culture as unalloyed virtues. Yet when it comes to “fixing” mood, all of these special human assets can turn into liabilities, with the unintended consequence of making depression worse.

Sinking Through Thinking

A hallmark human response to low mood is to try to explain it—as we do with moods generally. We use language to construct theories about where painful feelings come from. The basic idea is, “If I understand why I feel bad, I will know how to fix it.” This impulse makes sense. It fits with a main function of low mood, which is to help draw attention to threats and obstacles in unfavorable environments. In a low mood, behavior pauses and the environment is analyzed more carefully.

However, exactly what “analyze more carefully” means depends on which species is doing the analyzing. The schnauzer, Ollie, just separated from his sister, may sit at the window for hours looking for signs of her return. Visual search is the sum total of his environmental analysis. When a human pines for a loved one, say a mother missing her son away at summer camp, the analytical field is far wider. Our outsized language capability draws in thoughts linked to the situation: “That head counselor seemed awfully young.”; “Did I remember to pack sunscreen?”; “I wonder why we haven’t gotten a postcard?” These thoughts may then trigger further mental images—a flash of Tommy drowning, the funeral—as well as feelings—a pang of guilt for ever letting him go to Camp Meadowlark in the first place.

Such reflections on mood have a purpose beyond self-flagellation. The mood system is practical and most interested in what to do next, in finding the action that will enhance fitness. What people brood about is not random but tracks key evolutionary themes (finding a mate, staying alive, achieving status, defending kith and kin, etc.). Mothers and fathers worry about their children at summer camp because mistakes in child rearing are evolutionarily costly. A mother who figures out that she’s dwelling on a failure to pack sunscreen can send a remedial Coppertone care package, and, the next time Tommy is sent away, he’s more likely to be fully provisioned. Even the most backward-looking counterfactual thinking (coulda, shoulda, woulda) has a forward-looking element: understanding why bad things happened helps us prevent their recurrence.

Reacting to low mood with thinking has evolutionary logic; it enhances survival and reproduction (fitness). Sadly, what’s good for fitness is not necessarily good for happiness. Only sometimes does thinking about mood enhance happiness. We see this fairly reliably in certain brands of psychotherapy, in which the process of thinking about mood and discovering its meanings is specially structured and guided by an expert. For a novice to think his or her way out of low mood and depression to get to a happier place—that’s a dicier proposition. Humans are understandably confident when trying to think our way out of a low mood. We solve so many other problems by thinking, such as how to get a stalled car to start or how to make a healthy meal out of scraps in the fridge.

Becky, a college professor in Maryland, organizes a team to analyze old production data from a distillery to figure out the determinants of good whiskey quality and use this information to ascertain why the distillery’s product loss between brewing and bottling is nearly twice the industry standard. She is now in an episode of depression. Every morning Becky wakes up and says to herself, “What can I do today to solve this problem?” But even with a PhD degree, considerable insight, and bookshelves filled with self-help books, her depression hasn’t budged for thirteen months. If you speak with her, even in her depressed state, it is immediately obvious that she is intelligent. On paper, she has every reason to believe that she can solve her depression.

Yet most humans, including Becky, are not nearly as good at this as they think they are. And our confidence in thought makes it more difficult to recognize when thinking is not working. The pitfalls of such an approach are underappreciated. In fact, “thinking your way out” might actually provide new ways in, new ways for low mood to deepen into serious depression.

Our advanced language and ability to hold ideas in mind, called working memory, combine to create a formidable meaning-making machine. Yet this machine can be too productive for our own good. It can easily churn out new interpretations of a troubling situation well after the situation has passed. On Friday, a worker can still be mulling over her boss’s hostile comment from Monday and wonder, “Maybe it was that e-mail I sent three weeks ago that set him off.” Once the meaning-making machine is in overdrive, a bad mood can prompt a potentially unlimited number of implications. We can generate dozens of seemingly plausible environmental reasons for the question: “Why I am so blue?” (My job is boring. I need to lose weight. We can’t stop global warming.) Even if you are feeling only a tiny bit sad right now, take sixty seconds to try this yourself. I doubt you will draw a blank on possible reasons. You’ll have leads. Yet many of the leads will be false, that is, irrelevant to the real source of the mood. When the real source of low mood is a thyroid deficiency or a low-grade infection, an analysis of the environment is moot. Or worse than moot, because with all the attention we pay to the false leads (all the reasons I hate my job), we may find fresh reasons to feel low. The generation of false leads may be good for fitness (the value of an exhaustive search), but it’s not always so good for happiness.

Given our natural reliance on and our confidence in thought, the urge to repetitively think about the causes and consequences of low mood can harden into a habit. Researchers label this habit of thought rumination. Some people enter a ruminative mode even when facing minor troubles, or even when their environment is benevolent. A consistent body of data—much of it collected by the late psychologist Susan Nolen-Hoeksema—shows that this is a dangerous habit. People who report a greater tendency to ruminate on a short questionnaire have longer periods of depressed mood in everyday life, are more pessimistic about the future, and have a harder time recovering from the effects of stressors such as a natural disaster or a recent bereavement.

The human meaning-making machine is so good at what it does that it can generate interminable interpretations. When persistent thinking gets stuck, it does not arrive at a stable theory of the problem, does not solve it, and cannot come to terms with it. Far from engaging in active problem solving, a person may simply perseverate on the fact of the problem (or problems) for months on end.

When the meaning-making machine gets caught in this way, its analysis turns inward, shifting its focus from a problematic environment to a problematic self. Analyses of various kinds of thoughts have found that those that repeatedly focus on the failings of the self are the kind most closely linked to depression. Insistent problem solving by itself is not necessarily harmful. In fact, therapeutic techniques that bolster active problem solving (say by breaking a problem down into structured subparts) can be helpful for depressed persons. It’s the deconstruction of the self that really causes trouble.

As Homo sapiens sapiens, we know, and we know that we know. An elaborate conceptual self—another thing that’s usually a point of pride—becomes a vulnerability. We’re committed to our autobiographical self, our story. It’s as if we have films of our own lives playing in our heads, with us cast as the heroes. Depressed people, however, recast their movies with themselves as villains and play them in an endless loop. A depressed chimp, lacking a deep autobiographical self, is spared this screening and will never have the experience of lying awake at night thinking, “I am a terrible mother.” Our capacity to dwell on our own failings makes us more vulnerable to depression than our fellow mammals.

Humans also have a special category of failings because of our heightened ability to self-monitor: our failures to change mood. This was true for Becky, who said of herself, “As a goal-oriented person, I keep looking for (and trying) things I can do to snap out of the depression. Medication, meditation, sleeping pills, trying to spend time doing ‘things that bring me joy’ (which just backfires, because I end up feeling hopeless while I’m doing them).” Every day that the depression goes on, failures to change mood turn into nagging thoughts: “Why can’t I just get over this?”; “Why am I so weak?” These self-monitoring statements become further fodder for rumination, which becomes further fodder for depression, and we are reminded once again that our powers of language are a decidedly mixed blessing.

All Cheered Out: Culture and the Pursuit of Happiness

We are the only species to look to culture to guide us on what feelings are desirable and how undesirable feelings should be managed. And as humans try to “fix” low mood, they are never alone. No creature ever living has had available so much advice—spiritual, medical, psychological, folk-inspired—about what to do when it’s feeling down. In the past fifteen years we have seen an ever-growing stream of psychological and popular science books examining happiness and how people can increase it. Ideally, these resources should serve as bulwarks against depression. Perversely, the opposite may be the case. Our predominant cultural imperatives about mood, though surely well-intentioned, are worsening the depression epidemic.

In the West there is a powerful drive to experience happiness. This tradition is particularly strong in the United States. Indeed, it’s difficult to think of anything more American than the pursuit of happiness. Along with life and liberty, it’s written into the Declaration of Independence as a fundamental right. Wanting happiness is as American as apple pie. But how happy should we expect to be? Happier than other people around the globe?

It would appear so. Analysis of thousands of survey responses found that when people in different countries were asked to rate how desirable and appropriate it is to experience varying psychological states, positive states like joy and affection were rated more desirable and appropriate in Australia and the United States than in Taiwan and China. Cross-cultural research by Jeanne Tsai of Stanford University has also found that European Americans place the highest value on specific forms of happiness, idealizing states like enthusiasm or excitement, termed high arousal positive states. By contrast, Chinese and other Asian test subjects place the highest value on other forms of happiness, idealizing states such as calm and serenity, termed low arousal positive states.

Consistent with the notion that culture inculcates ideals about feeling states, cultural differences show up early in life. When young children judge smiling photographs, American children prefer the expression that shows an excited smile to the expression that shows a calm smile. Taiwanese children do not show this same preference. American preferences for high arousal positive states probably have many roots, but they stem in part from a media environment that values peppy happiness. An image analysis of smile photos in American women’s magazines found that they contained more excited smiles and fewer calm smiles than smile photos in Chinese women’s magazines.

So what’s the problem? Everyone I know wants to be alive, free, and happy. What’s wrong with pursuing happiness to the fullest extent possible? The more you value your happiness, the happier you’ll be, right?

Wrong, says compelling recent research.

Two studies led by psychologist Iris Mauss found evidence for an alternative hypothesis: people who value happiness more are less likely to achieve their goal of feeling happy. In the first study the researchers administered a questionnaire designed to measure the extent to which people valued the experience of happiness as a fundamental goal. Mauss and colleagues found that some people put an especially high value on happiness, endorsing items like, “If I don’t feel happy, maybe there is something wrong with me”; and “To have a meaningful life, I need to feel happy most of the time.” Surprisingly, women who said that they valued happiness more were actually less happy than women who valued it less. Specifically, women who valued happiness highly reported that they were less satisfied with the overall course of their lives and were more bothered by symptoms of depression. Strangely enough, valuing happiness seemed most problematic for women whose lives were low in stress—the people for whom happiness should have been within easiest reach.

The second study was a clever experiment in which the researchers tried to briefly increase how much the participants valued happiness. They did this by having one group of participants read a bogus newspaper article that extolled the importance of achieving happiness (the other group read an article that did not discuss happiness). Later in the experiment participants watched different short films. Those women who had read the happiness-extolling article reported feeling less happiness in response to a happy film. The authors again concluded that, paradoxically, valuing happiness more may lead people to be less happy, especially when happiness is within reach.

These experiments help us understand why predominant cultural imperatives about mood might be worsening the depression epidemic. Our current cultural ethos is that achieving happiness is like achieving other goals. If we simply work hard at it, we can master happiness, just as we can figure out how to use new computer software, play the piano, or learn Spanish. However, if the goal of becoming happier is different from these other goals, efforts devoted to augmenting happiness may backfire, disappointing—and potentially depressing—us because we can’t achieve our expected goal. Mauss and colleagues concluded that setting a goal to become happier is like putting yourself on a treadmill that goes faster the harder you run.

Rising happiness standards widen the gap between what we want to feel and what we actually feel. We know from Jeanne Tsai’s work that people in the West generally idealize excitement and other high arousal positive states. Although this is a general tendency, she has also shown that people vary in how strong their positive ideal is. Importantly, for people who have that strong positive ideal, there is potentially a large gap between what they would like to feel and what they actually feel. The size of this gap predicts depression. People who have a larger gap between their ideal and actual positive affect have more depressive symptoms.

This is not surprising: to someone with high happiness goals, low moods are as demoralizing as a foreclosure notice is to an aspiring billionaire. If you believe that a high positive mood should be easy to achieve, a prolonged low mood is an insult, which probably prompts the isolating and stigmatizing question: “What’s wrong with me?” Negative feelings about negative feelings make them a greater threat. People who set unrealistic goals for mood states may be less able to accept or tolerate negative emotional experiences like anxiety or sadness. Oddly enough, being able to accept negative feelings—rather than always striving to make them disappear—seems to be associated with feeling better, not worse, over the long run. There is evidence that when people accept negative feelings, those experiences draw less attention and less negative evaluation than they would otherwise. Some research shows that people who report an ability to accept negative feelings when they arise are less likely to experience depressive symptoms in the future.

Ultimately, the strong cultural imperative toward being happy bumps us up against a wall: our mood system is not configured to deliver an end state of durable euphoria. Happy euphoria is a reward the mood system metes out along the way, on the road to pursuing other evolutionarily important goals. For example, euphoria is a reward for having sex or for when your first-choice date to the prom says yes. By design, these rewards are meted out sparingly rather than liberally.

Yes, pleasure after eating the carrot rewards the bunny for finding the carrot, yet a well-designed bunny does not stay satiated. It’s the end of the pleasure and the promise of more that gets the bunny hopping off to find more carrots and ultimately to survive long enough to make more bunnies. So clearly does intense happiness fade after a goal is achieved that psychologists and economists have given the experience its own label: hedonic adaptation. It is powerful, and studies show it to be virtually omnipresent: whether after purchasing a zippy new sports car, getting a big promotion, or moving to a cool new apartment, with time (often surprisingly little) the euphoria fades.

Hedonic adaptation and our unattainable cultural imperatives make for a cruel combination. People will usually fall outside the zone of intense pleasure, and they will consider that failure. In this scenario, shortcuts are tempting. Forget having to realize an evolutionarily important goal and just give me the pleasure now, please. The high from smoking crack is almost immediate, but it does not last. In the long run, the shortcuts backfire. The mood system has the last word.