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Abstract
Anyone who has suffered from depression, or watched a loved one struggle with its paralyzing pleasurelessness and hopeless moods, may find it hard to believe that such a state could be an evolutionary adaptation. How could Darwinian selection favor the "black dog"?
| How could Darwinian selection favor the "black dog"? |
Evolutionary psychologists have several overlapping theories. While they stress that not all depression is adaptive, and that something that was adaptive in the Paleolithic may not be so useful now, all believe that understanding the syndrome's evolutionary origins could improve both talk and pharmacological therapies.
Based on observation of both humans and nonhuman primates with hierarchical social structures, John Price, an English psychiatrist (now retired), proposed in 1972 that depression serves as a submission signal. When an animal suffers a defeat and slides down the hierarchy, stress hormones rise and serotonin levels fall - a chemical signature of most depression.
"Depression makes people feel inferior," says Price. "It makes them feel that a low rank is appropriate [so that they behave accordingly]. The important thing to grasp is that the basis of mood change is to alter strategies of escalation and de-escalation in competitions."
| Depression may nature's way of escaping losing situations. |
Price points out that mood often shifts independently of rational thought. "A patient may be suffering because at the top level [his rational thoughts and plans], he is escalating his competitive strategy, but he is not winning; and the experience of being insulted or struck gets through to his [emotional] brain, which decides to de-escalate."
Depression can be adaptive, Price says, when it removes an animal or person from a losing situation. By showing signs of submission and withdrawal, the animal can avoid the danger of being injured by a dominant individual and can wait to fight for resources or mates until it has a better chance of winning.
| "Non-anxious subordinates get pounded." |
Paul Gilbert, professor of clinical psychology at the Institute of Behavioural Sciences of Derby University in England, notes that the submission theory accounts for the way anxiety and depression are often inextricably linked. "Lower-ranking animals have stress from above," he says. "They need to be more anxious and wary because otherwise they get in trouble. They need lower confidence, because non-anxious subordinates get pounded."
This theory also sheds light on the connection between depression and low self-esteem. "Depressed people are more withdrawn and they don't feel as lovable, attractive, etc., as others," says Gilbert.
| Is depression anger turned inward? |
The idea that depression is anger turned inward also fits with this: depressed people often bottle up their anger toward their superiors and take it out on themselves, although they may also express more rage and hostility toward those below them on the totem pole.
Gilbert points out that inescapable stress can often contribute to depression. "An animal with social stresses can get away, he can avoid the dominants; but human society often traps people. A human who is being abused by a boss or spouse is not always able to escape."
| "Chronic, inescapable stress does bad things to you." |
Abused children are trapped in just such a situation - and the abuse constantly tells them that they are worthless and inferior. Not surprisingly, having been abused puts people at high risk for depression.
Psychologists - starting with Martin Seligman - have shown that it is the lack of control over a situation that helps stress create depression. Says Gilbert, "Chronic, inescapable stress does bad things to you. Like diarrhea and vomiting, stress hormones are useful in the short term, but for any length of time they [do real harm]." Studies have shown that high doses of stress hormones actually damage brain cells in the hippocampus - and interestingly, antidepressants seem to stimulate the release of nerve growth factors in this region. Researchers have recently been looking beyond neurotransmitters and into hormones and growth factors as possible areas of intervention for depression.
An ongoing study of thousands of British civil servants has found that the health effects of rank aren't limited to psychiatry. Lower-ranking employees have higher levels of coronary artery disease and chronic bronchitis as well as depression - and low status has an even stronger deleterious effect on health than does smoking.
| In humans, self-conscious rumination reinforces depression. |
For humans, unlike other animals, there's the added problem that they can obsess about their status and this can reinforce the physiology of depression. Says Gilbert, "Imagine you are lying in bed thinking sexual thoughts. Your own fantasies can generate hormones and arousal. But what happens if you are ruminating and fantasizing that you have no future, that you are inferior? It simply [ratchets] up your stress hormones."
Gilbert doesn't see this self-reinforcing aspect of depression as adaptive, and believes that medications are often crucial to changing the physiological climate of the brain to allow more positive thoughts to arise. Cognitive therapies can then help the person develop a better strategy to cope with competition - either by working on ways to win or by finding ways to shift to more attainable goals.
Price agrees, but has some concerns about using medications in all circumstances. He cites the example of a depressed farmer he treated, who was in conflict with his son about the future direction of the farm. While depressed, the father resigned himself to ceding control over the property. "But I don't know what would have happened if we had given him antidepressants first, whether he would have gotten more stubborn [and made the situation worse]," Price says.
| "The function of depression is to get people to give up unwinnable fights." |
"The function of depression, as I see it, is to get people to give up unwinnable fights - until [they give up], it has a function," Price concludes.
Gilbert says there is not enough research to determine whether antidepressants tend to make people fight longer for the unattainable or move on. "To be honest, I don't think it is well studied," he says. He suggests that someone should study whether people in bad marriages who take antidepressants are more likely to stay with their spouses because the drugs make it bearable, or to leave because the drugs give them new confidence. "It's a question worth asking."
Unprompted, University of Michigan psychiatry professor Randolph Nesse, director of the Evolution and Human Adaptation Program at the university's Institute for Social Research and originator of a broader evolutionary theory on depression, suggests the same experiment. "My clinical guess is that they are much more likely to get out," he says.
| Mood is related to how well goals are being met. |
Nesse's theory suggests that depression doesn't have just one function; rather, mood is related to how well goals (whether status-related or not) are being met. Depression occurs when situations are not propitious for either the current life strategy or a switch to a new one.
Says Nesse, "Some depression may be tied up with the role of mood in regulating behavior when you are pursuing a goal you can't reach. The motivation to stop or get out grows, just as your motivation to breathe grows when you hold your breath. The system is trying to get you to stop doing something, but you put more and more effort into doing it."
"If the mechanism works," he continues, "The bad feeling goes away when you change your goal. The deep problem with the theory that depression is useful is that then why doesn't it get you out of the bad situation?" Nesse speculates that depression may be paralyzing because our ancestors may have faced many situations in which giving up too soon and starting something new immediately was disadvantageous; hence a syndrome which retards almost all action.
Nesse stresses, however, that a lot of depression "is disease. People think that evolutionary approaches involve treating people like animals, but this kind of evolutionary approach encourages great attention to individuals, to their lives and loves and what's meaningful to them. It gets us back to meaningful contact." Medications are useful, he believes, but should not just be handed out without further thought.
| Postpartum depression may signal whether to support a newborn child. |
One type of depression that may have a particular adaptive function is postpartum depression (PPD). "The [evolutionary] problem in the case of postpartum depression is whether or not to invest in this particular child," says Ed Hagen, a postdoc studying the condition at the University of California at Santa Barbara. "It is very clear that mothers and fathers do make a decision [of this sort]. Important factors in the decision [for the mother] are how healthy is this baby, how many kids do I already have, and how much support is there from the father and others."
All of these factors are related to the incidence of PPD. Studies find that the less support a woman has and the less healthy she perceives a baby to be, the higher her likelihood of suffering PPD.
| Early in evolutionary history, infanticide was common. |
Early in evolutionary history, infanticide was a common solution - and those who chose it appropriately may have been more likely ultimately to have greater numbers of surviving children. Modern society, of course, strongly stigmatizes infanticide, often with legal penalties. If it is indecision over investment - rather than unhappiness over abandoning the child - that causes depression, one would predict that the incidence of PPD in hunter-gatherers would be relatively low; but as yet there is no data on this question.
Hagen sees PPD as a test case for theories of depression in general, which he views as a negotiating tactic, not a signal of submission. "It's plausible to suggest that if mothers are constrained and can't just walk away, their only strategy to get others to invest more in [a] child is to 'go on strike' and say [via the depression], 'If you don't help me, I won't do anything.' It's a last-ditch strategy; it's completely unconscious, and not deliberate or manipulative," he says.
| PPD increases paternal support for mother and child. |
Hagen finds that PPD does cause others to invest more - the father and other relatives almost always increase support for mother and child in such situations. "My clinical impression is that if the mother is assertive and negotiates support before the baby is born, there is a lower chance of PPD."
He sees some support for the status theory, but says, "The threat of suicide doesn't make sense in a submission model, but it does in a bargaining model. If I'm a mother, I offer the benefit of caring for the new child, existing children, future children - and if I die or defect, that's all gone, so you'd better change [and help out]."
Opponents of the idea of depression as bargaining say that the condition is so unattractive that it can just as easily have the effect of pushing people away as attracting help. Hagen acknowledges this, and says, "It's a hardball negotiating tactic, a last resort."
As far as PPD treatment strategies are concerned, the bargaining idea suggests that involving other family members in therapy and helping the mother learn to assert her needs would be useful.
Though skeptics may see evolutionary theories of depression as adaptationism gone overboard, they are certainly far less outlandish than many Freudian ideas that still pervade psychology. At least more research here could offer practical answers to questions about the social effects of antidepressants - and perhaps new ideas for medications and talk therapy development.
Maia Szalavitz is a health/science journalist who has written for the New York Times, the Washington Post, Newsday, New York Magazine, Salon, and other major publications.
Cary Barnhard grew up in New Jersey, where his senior class voted him "most unique." He maintains that honor is a polite way of being voted "most likely to need therapy." After a few misadventures in the music industry, he started pretending to be a graphic artist. Eventually it became the truth.
Good Evolutionary Reasons - considers the evolutionary explanations for depression in women. Written by Patricia Greenspan of the University of Maryland.
Diagnosis and Evolutionary Theory - a more general introduction to using ancestral behavior as a diagnostic tool for modern life. By James Brody; from Behavior Online.
Update on the Neurobiology of Depression - includes the role played by stress hormones. From Medscape (free registration required).
The Functions of Postpartum Depression - a detailed article, including evolutionary hypotheses, by Edward Hagen.
Depression and Postpartum Depression - resource guides from MEDLINEplus.
Evolution and the Origins of Disease - a discussion of evolutionary approaches to medicine by Randolph M. Nesse and George C. Williams. From the November 1998 issue of Scientific American.
Novel strategies for pharmacotherapy of depression - includes a discussion of treatments targeting the stress hormone corticotrophin-releasing factor. From Current Opinion in Chemical Biology, 1999, 3:481-488. Full text available from BioMedNet.
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