The anthropologist John Hartung independently proposed an interesting variation, with the intriguing designation of “deceiving down.” He notes that being subordinate to someone with lesser abilities is a perilous situation. The natural inclination to show one’s stuff will be perceived as a threat, likely resulting in an attack or even expulsion from the group. The solution? Deceive down; that is, deceptively conceal your abilities.26 The best way to do that is to convince yourself that you are less worthy and able than you are, a pattern similar to the neurotic inhibition and self-sabotaging that Freud attributed to castration anxiety.
Further support for the connection between status losses and depression comes from the extraordinary data gathered by the British epidemiologists George Brown and Tirril Harris.27 In their detailed studies of women in north London, they found that 80 percent of the women who developed depression had experienced a recent life event that met their careful definition of “severe.” Of all women who had experienced severe life events, only 22 percent developed depression; however this rate is twenty-two times higher than the 1 percent of women who do not experience such an event. Of the women who had experienced a severe life event, 78 percent did not develop depression during the next year, leading to new studies of “resilience.”28 This careful research provides superb evidence for the role of life events causing depression. Scores of newer studies confirm and extend the role of life events in causing depression.29,30,31,32,33,34,35,36,37
Some events are much more likely to precipitate depression than others. In the Brown and Harris study, an episode of depression occurred after 75 percent of events characterized by “humiliation or entrapment” but only 20 percent of loss events and 5 percent of danger events.38 These data support Price’s theory nicely, especially if humiliation or entrapment is assumed to involve status conflicts. Describing specific life situations vastly increases predictive power compared to generic measures of life events or “stress.”
The involuntary yielding hypothesis seems correct for many cases of depression I have treated. Myriads of spouses limit their achievements, and even their view of their own abilities, to preserve their marriages. The deceiving-down social strategy prevents attacks by those with more power, at the price of depressive symptoms. An ambitious young lawyer I treated did not use deceiving down; he gave a brilliant presentation that upstaged an ineffective senior partner—who subsequently proved to be very effective at derogating the work of the young upstart, who was soon depressed.
The function of signaling yielding to prevent attack can be reframed in terms of the situation in which it is useful: loss of a status competition. This allows consideration of other ways in which low mood might be useful in that situation: reassessing social strategies, considering possible alternative groups, investing more in selected potential allies, or withdrawing socially until a better time.
Even when reframed as a response to a situation, however, the theory remains specific to one domain—social resources—and one aspect of that domain—social position in a hierarchy. Fighting an unwinnable status contest is one subtype of the more general situation of failing to make progress in the pursuit of any goal. After a status loss, signaling submission stops attacks by those with more power. What about failing in other efforts? Is preventing attacks after a status loss the main function of depression symptoms?
My experience with patients suggests not. Even within the domain of social status, depression symptoms do things other than signaling submission, such as motivating consideration of alternative strategies and new alliances. Also, while about half of my patients with depression seem to be trapped pursuing unreachable goals, many of those goals are not about social position. Is unrequited love a pursuit of a status goal? What about trying to find effective treatment for a child with cancer?
Debate won’t answer such questions; we need data about what events and situations give rise to which symptoms of depression. Billions of dollars have been spent in the search for brain abnormalities in people with depression and millions investigating the role of “stress.” It is a great scientific embarrassment and tragedy that funding agencies have not allocated the resources needed to discover exactly what kinds of life events and situations cause exactly which depression symptoms.39,40,41
Increased thinking about one’s problems is characteristic of low mood. The thinking is often actually rumination. The problem goes around and around in the mind without ever reaching a solution, like a wad of grass that a cow chews, swallows, regurgitates, and chews again. One of my former colleagues, the psychologist Susan Nolen-Hoeksema, viewed rumination as a maladaptive cognitive pattern that is central to depression and best stopped if at all possible.42 In an astounding but tragic bit of luck, she gathered data on depression and tendencies to ruminate just before the 1989 Loma Prieta earthquake in California. Interviewing the same subjects again after the earthquake revealed that those who had a tendency to ruminate were more likely to have become depressed, even when other predictors of vulnerability to depression were controlled.43
In a widely discussed 2009 article in Psychological Review, biologist Paul Andrews and psychiatrist J. Anderson Thomson, Jr., proposed nearly the opposite view.44 They argued that rumination helps to solve major life problems. In their view, depression withdraws interest from action and outer life to free up time and mental energy for ruminating to solve the problem. This article extended a related proposal Andrews and biologist Paul Watson had made in a 2002 article, that depression evolved to serve the function of “social navigation.”45 In a firm critique of these ideas, the Newcastle University evolutionary psychologist Daniel Nettle pointed out that there is little evidence that rumination solves social problems, or that depression speeds finding solutions.46 The Norwegian evolutionary clinical psychologist Leif Kennair concurs, and I agree with their critique.47
Nonetheless, social withdrawal and thinking a lot can be useful when one encounters a dead end in life. I greatly admire a 1989 book by the Swedish psychoanalyst Emmy Gut entitled Productive and Unproductive Depression: Its Functions and Failures.48 Using vivid case studies based on historical figures, she argued that depressive withdrawal and intense cogitation can improve coping when major life problems require a major change but can also leave some people stuck in unproductive depression. Major life failures may motivate allocating enormous effort into finding new strategies. However, as Gut, Nettle, Nolen-Hoeksema, and others note, rumination and withdrawal are not reliably optimal responses to such situations.
The functions summarized in the previous paragraphs are some of the most compelling that have been proposed to explain low mood and depression. Framing these functions as alternatives has motivated much useless debate; all may be relevant. However, their significance and relationships to one another become clearer when the frame shifts from their functions to the situations in which they can be useful.
Mood Adjusts to Cope with Changing Propitiousness
Most behavior is in pursuit of a goal. Some efforts are attempts to get something, others to escape or prevent something. Either way, an individual is usually trying to make progress toward some goal. High and low moods are aroused by situations that arise during goal pursuit. What situations? A generic but useful answer is: high and low moods were shaped to cope with propitious and unpropitious situations.49 A propitious situation is a favorable one in which a small investment gives a reliably big payoff. If a herd of mastodons is coming down the valley, exuberant pursuit will likely be worth the effort and risks. If your job is selling new cars, extra effort in a boom year will pay off. In an unpropitious situation, efforts are likely to be wasted. If no mastodons have been sighted for months, expeditions to look for them will likely waste time and energy. Trying to sell cars during an economic downturn is not as fruitless, but it is no fun.
Individuals whose mood rises in propitious situations can take full advantage of opportunities. Individuals whose mood goes down in unpropit
ious situations can avoid risks and wasted effort and can shift to different strategies or different goals. The capacity to vary mood with changes in propitiousness gives a selective advantage.
The story gets more interesting fast. When times are good and likely to stay that way, there is no need for exuberant effort now. If mastodons come by every day, seeing a herd is no reason to get excited. If your crop can be harvested anytime, relax. But if mastodon sightings are rare, intense effort now will be worth it. It seems paradoxical, but intense high mood is valuable mainly for short-lived opportunities. Low mood is more useful for temporary unpropitious situations than indefinite bad times. People who experience sudden big losses improve with time, but the distortions of depression often make that impossible to see.
Life’s Three Decisions
Making three decisions well is all it takes to maximize fitness. The challenge of picking wild raspberries illustrates how mood helps to make these decisions well. First, how much energy should go into your efforts at the current bush? Should you pick berries as fast as you can or at a leisurely pace? Second, when should you quit? Is it better to keep picking berries from this bush or to stop and look for another one? Finally, when it is time to do something else, what should you do next? Gather another kind of food, do something else, or go home?
Our lives are sequences of such decisions on varying time scales. Should I keep editing this paragraph or move on to the next one? Should I keep writing or take a break for lunch? Should I keep trying to write this book or give up and take up golf? My writing is slowing and my enthusiasm is waning, so now is a good time for lunch.
There, that’s better. A brief break refocuses attention to a slight variation on the central question: Why are people who lack the capacity for mood at a disadvantage? Mood variation does not have to exist. We could go about our days in a steady state, neither enthused by unexpectedly finding a tree laden with ripe fruit nor discouraged by walking for hours to find a tree empty. We would experience neither the excitement at smiling, steady eye contact from the most attractive person in the room nor the deflation upon realizing that the invitation was intended for someone else. Without a capacity for mood, neither winning the lottery nor going bankrupt would influence levels of energy, enthusiasm, risk taking, initiative, or optimism. How best to pick berries offers a model for much else in life, even intensely personal decisions such as deciding whether to continue in a job or a marriage.50
Berry Picking and Mood
If you have ever spent an afternoon picking wild raspberries, you have experienced the emotional changes that guide foraging. Finding a bush laden with ripe fruit arouses a tiny thrill. With joyful enthusiasm, you pull off berries in handfuls, some of which are so delectable they never make it to the bucket. As the bush gets depleted, the berries come more slowly, then slower yet. Enthusiasm wanes. Finally, you are reaching through prickles to try to get that one last deformed berry. Your motivation for picking from this bush is gone, and a good thing, too. It is senseless to try to get every berry from every bush. However, jumping too quickly from bush to bush is also unwise. How long should you stay at each bush to get the most berries per hour? The problem may seem abstract, but making such decisions well is crucial to the fitness of nearly every animal.51
The mathematical behavioral ecologist Eric Charnov came up with an elegant solution, one that illuminates much about mood in everyday life.52 To keep things simple, assume that it always takes the same amount of time to find a new bush (Search Time on the graph). When you find a bush, berries come fast at first, then slower and slower yet; that is why the curved line is steep at first, then slowly levels off. You can stop picking at any time along that curve. The longer you stay, the more berries you get from that bush, but to get the most berries per hour, you need to stop and go looking for the next bush at just the right time.
The best time to stop is at the point that gets you the most berries per hour. The number of berries is the height (the dotted vertical lines), and the time is the width (Search Time plus Picking Time), so you will get the most berries per hour if you stop at the point where the line with the steepest slope (the solid one) just touches the top of the curve. If you leave sooner (the lower dashed line), or stay longer (the higher dashed line), you will get fewer berries in an hour.
The Marginal Value Theorem
Charnov called this the Marginal Value Theorem, because all the action is at that spot “on the margin” where the rate of getting berries at the current bush dips below the number of berries you can get per hour by moving to a new bush. The core idea is simple but profound. You don’t have to do calculus to get the right answer, you just need to follow your emotions. To maximize the number of berries you get in a day, go looking for a new bush whenever you lose interest in the current bush. Thanks to your emotions having been programmed by natural selection, that will generally be the point at which the rate of berries coming from the current bush slows to the average number per minute across many bushes. This decision-making mechanism is built into the brains of nearly every organism. Ladybird beetles, honeybees, lizards, chipmunks, chimpanzees, and humans all make such foraging decisions well. No calculation is needed; motivation flags at the optimal time to make a switch.
The decision about when it is best to quit one kind of activity and do something different follows the same principle. If bushes and berries are so sparse that you are spending more calories each hour wandering about than you are getting from picking berries, the best thing to do is to quit. Even if berries are plentiful, there comes a time when quitting is best, because if you already have a thousand, picking more means lugging a heavy bucket and spending whole days in the kitchen making more jam than you can eat in a year. Well before that point, motivation turns negative and sensible people head home.
The Marginal Value Theorem sets the rhythm of our days. We start an activity with gusto, stay with it awhile, then lose interest and move on to something else. How long we stay depends on the start-up cost, which is equivalent to the cost of finding a new berry bush, how the payoffs decline with time, and the payoffs of available alternatives. To read a book, for instance, you need to find the book, settle into a chair, turn on a light, and start reading. If you jump up to do something else after just a few minutes, you will never read much.
People with attention-deficit/hyperactivity disorder (ADHD) know this all too well. Their motivation for the current task fades fast, and new opportunities glow brightly, like neon invitations. They shift quickly from one activity to another, rarely getting much accomplished. It would be interesting to study how people with ADHD forage for berries. I bet they quit each bush too quickly. However, staying too long is also unwise. People who persist excessively also deserve a diagnosis: attention surplus disorder.53 Interestingly, drugs used to treat ADHD increase dopamine, the same substance released in the brain in response to rewards. Increasing dopamine may make the brain respond as if more berries are coming per minute from the current bush, encouraging persisting at the current task.
When to Quit All Activity
When to quit all activity and go home—or never to go out in the first place—is a related decision that brings us closer to low mood and depression. The general answer is simple: when you are spending more calories each minute than you can get from any possible activity, it is best to go home and wait for a better time.
Bumblebees gather pollen and nectar every minute on warm summer days. As evening comes, cooler air makes flying more costly, and flowers close and become harder to find. At some point in the gathering dusk, it is best to go home. Bumblebees make this decision superbly.54 Their ancestors who quit too soon or persisted too long got fewer calories per day and so had fewer baby bumblebees. For a rabbit, the principle is the same, although the cost of staying out too long is more dramatic: becoming dinner for a fox. For all species, when the expected costs are greater than benefits for any possible activity, the best thing to do i
s . . . nothing. Don’t just do something, stand there! Find someplace safe and wait for a better time. This analysis gets us closer to low mood and depression.
Some animals go into a dramatic conservation state nightly. The stripe-faced dunnart is a mouselike Australian marsupial that lives in desolate deserts where food is scarce and temperatures fluctuate widely. It can’t get enough calories in a day to keep its body warm through cold winter nights. So its metabolism slows after dark, dropping its body temperature 20 degrees in a bout of minihibernation.55 Sometimes the best strategy is doing even less than nothing.
Other animals must make life-and-death decisions in which taking big risks is best. In a classic experiment, the behavioral ecologist Thomas Caraco and his colleagues let juncos learn that they could find seeds at two bird feeders. Both gave the same average number of seeds per visit, but one gave a tiny consistent payout every time, while the other gave a payout that varied widely. In ordinary temperatures, the birds preferred the sure-thing low-payout feeder. But when the temperature decreased below the point that made survival through the night unlikely on the calories provided by the consistent but low-payoff feeder, they switched. Instead of freezing to death for certain, they took a risky bet that offered some chance of survival, like otherwise doomed prison camp inmates who run for the fences despite guards with guns.56
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