In an era of tight budgets, supporters of depression research argue that more funding is needed to find a cure. That's logical-sounding but may be totally wrong. Depression's toll has risen even as more research and treatment resources have been poured into combating it.
Some 38 million American adults struggle with depression. The World Health Organization projects that by 2030, the amount of disability and life lost due to depression will be greater than that from war, accidents, cancer, stroke, or any other health condition besides heart disease. Richard A. Friedman recently wrote, "Of all the major illnesses, mental or physical, depression has been one of the toughest to subdue." Despite 26 different antidepressants to choose from, only a third of patients with major depression will experience a full remission after a round of treatment. Newer antidepressants are no more effective than those developed nearly 60 years ago.
Our main approach to depression is biomedical and assumes that depression is an illness. Yet the search to discover a fundamental defect in the brain that causes depression has foundered. There remains no biological test to diagnose depression, despite hundreds of physical assays, nor are there any genes that strongly predict it. Brilliant scientists cannot find the defect—even if they look with different or more expensive toys—because their search is animated by the wrong question: Where is the disease?
We can understand the puzzling tenacity of depression by posing the opposite question: How has nature built us with the capacity to become depressed? Depression is a byproduct of evolution, which has shaped not only the physical structures of our bodies but the basic mechanisms of our minds. Mood is a key adaption that we share with other animals.
Moods have been selected for because they flexibly tune behavior to situational requirements. High moods lead to more efficient pursuit of rewards. Low moods focus attention on threats and obstacles and restrain behavior.
Moods are a clever adaptation because they integrate multiple aspects of how well or poorly we are doing. Moods track key resources in our external environment (like food, allies, and potential mates) and our internal environment (for example, fatigue, hormone levels, and adequacy of hydration). When conditions are unfavorable, or when goals are unreachable, low moods pause behavior to ensure that an animal does not engage in fruitless efforts. This efficiency is important given that resources of every sort—time, energy, or money—are finite.
Just as pain protects us from injury, the unpleasant aspects of low mood are in keeping with its utility. People in a low mood may blame and criticize themselves, turn situations that went wrong over and over in their heads, and experience pessimism about the future. These characteristics, although uncomfortable, are also potentially useful in that a keen awareness of what has already gone wrong can help a person avoid similar stressors in the future. Experiments reported by psychologist Joseph Forgas have provided some of the strongest demonstrations of ways in which low mood benefits thinking and decision making.
No adaptation is perfect. Adaptations present tradeoffs between benefits and costs. Our big brains have enabled our dominance over the planet and have also made childbirth far more dangerous. Our propensity toward anxiety is at once an important defense against threats and a lurking vulnerability to paralyzing conditions. Low mood is useful on average, but it has its costs. Inaction carries risk in a dynamic world. In more severe forms of low mood, these costs are higher, such as damage to the body from the release of stress hormones.
Why has depression become so prevalent? An ancient mood system has collided with a highly novel operating environment created by a remarkable species. Depression is worse in humans than in other mammals not because our species has more flaws but because of our unique strengths. Advanced language enables wallowing; our ability to set ambitious long-term goals sets up new opportunities for failure; our elaborate culture presents expectations for happiness that cannot possibly be fulfilled.
How will we better contain depression? Expect no magic pill. One lesson learned from treating chronic pain is that it is tough to override responses that are hardwired into the body and mind. Instead, we must follow the economy of mood where it leads, attending to the sources that bring so many into low mood states—think routines that feature too much work and too little sleep. We need broader mood literacy and an awareness of tools that interrupt low mood states before they morph into longer and more severe ones. These tools include altering how we think, the events around us, our relationships, and conditions in our bodies (by exercise, medication, or diet).
For the last 20 years we've been listening to Prozac. It's time to listen to depression.
Jonathan Rottenberg is the author of The Depths: The Evolutionary Origins of the Depression Epidemic, now available where books are sold.