Is depression an adaptation?
Article by: Nesse, R. M. (2000)
Archives of General Psychiatry, 57, 14-20

Abstract

In difficult situations, pessimism and lack of motivation may give a fitness advantage by inhibiting certain actions, especially:

• Futile or dangerous challenges to dominant figures
• Actions in the absence of a crucial resource or a viable plan
• Efforts that would damage the body
• Actions that would disrupt a currently unsatisfactory major life experience when it might recover or the alternative is likely to be even worse.

Introduction

Here are three causes for manifestations of disease

• Manifestations that arise directly from a defect in the body’s machinery
  Have no utility
• Defences or dysregulations of defences
  These are adaptations shaped by natural selection
• Dysregulated or extreme defences

Correcting a defect is almost always useful, but blocking a defence can be harmful.

Global evidence

Depression is painful and interferes with normal function.
Other useful capacities such as pain, nausea and fatigue, are also aversive and disruptive.
Their very aversiveness is likely a product of natural selection, probably because they promote escape and avoidance of situations that decrease fitness.
From that perspective, the intrinsic aversiveness of most low mood and depression suggest that they may be related to defence.

The epidemiology of mood disorders.
If depression were rare, and had symptoms unrelated to the experiences of most people, this would suggest it was a disease unrelated to any defence.
But this issn’t the case.
There is no point of rarity in the distribution that can differentiate pathologic from non-pathologic depression.
The incidence of depression is highest at the ages where reproductive value peaks, a pattern characteristic of few diseases.

Defences are regulated by cues associated with situations in which they are useful, defects are not.
The regularity of the relationship between loss and negative affect and the proportionality of low mood to the magnitude of a loos imply that mood is regulated.
The relationship of depression to events is less consistent. This suggests that many depressive episodes are not defences.

Possible functions of low mood and depression

Signalling benefits of several kinds have been attributed to low mood or depression.

Some suggest that depression in adults is a plea for help.  
There is few data to support this
Also, reactions to patients with chronic depression are mainly negative

It has been interpreted as a communication designed to manipulate others into providing resources.
As an attempt to an adaption that had failed, presumably because help was not forthcoming

Conservation-withdrawal: the presumed utility of the ‘despair’ phase of the behaviour pattern in a lost infant monkey.
Depression in adults after a loss has been interpreted as analogous to this pattern of infant behaviour.
Many depression has a role in conserving resources.
But, unlike hibernation, depression is rarely a state of calm conservation, does not affect all individual in a group synchronously, and with the possible exception of seasonal depression, is not usually corrected by the mere passage of time.

Grief and depression in adults as an epiphenomenon of attachment
But it remains to be determined whether grief is merely a design of constraint or an adaption in its own right

The utility of depression as a yielding signal in hierarchy conflicts.
Or a variation in which self-deception about one’s ability lulls superiors into thinking one is no threat.

A role of depression in disengaging motivation from an unreachable goal.
Control theory suggests that low mood motivates consideration of alternative strategies when the distance from the goal is being reduces more slowly than anticipated.
Low mood is aroused by a mismatch between achievements and expectations.

Mood regulates the allocation of effort and resources, toward enterprises, strategies, and times likely to give a high payoff and away from unprofitable enterprises and times when efforts will likely be wasted or dangerous.
If one is subject to a series of defeats, it pays to adopt a conservative game plan of sitting back and waiting and letting others take the risks.
Such waiting would be fostered by a pessimistic outlook.
If one is ranking in the chips of life, it pays to adopt an expansive risk taking approach, and thus maximize access to scare resources.

In what situations is low mood useful?

Emotions differ from one another because they are shaped to cope with different situations.
The global function of an emotion or affect is to create a special state in an organism that allows it to cope effectively with the adaptive challenges or characteristics of some situation that has recurred and influenced the fitness over the course of many generations.

Decreased motivation and activity would be useful mainly in situations in which action would be futile or dangerous.
Organisms carefully regulate when and where they exert effort.
Human behaviour is complex and organized around the pursuit of personal goals.
Psychologists have increasingly viewed emotions as arising from an individual’s appraisal of how an event will influence goal attainment.
Situations that regularly arise in the pursuit of goals arouse special states to deal with them effectively.
Failing to reach a goal is an especially potent elicitor of negative effect.
Low moods helps to disengage individuals from unproductive efforts.

Are the core aspects of depression ever useful?

Depression is characterized by a more pervasive pessimism, low self-esteem, and reduced initiative.

There are situations in which active efforts just make things works.
In such situations, it is often useful to inhibit any tendency to shift quickly to a different endeavour.
Depression inhibits futile efforts.

Depression is seen as a state shaped to cope with unpropitious situations.
It can be useful both to decrease investment in the current unsatisfying life enterprise and to prevent the premature pursuit of alternatives.
Failure to disengage can cause depression, and depression can make it harder to disengage.
This may explain why the low-mood system is so prone to getting stuck in positive feedback loops.
The costs of low mood may be small compared with those of inappropriate high mood. So in certain situations the ‘smoke detector principle’ biases the system toward low mood.

Usually, the dilemma is resolved by changing or accepting the current situation or by moving on.
When it is not, serious pathology may arise.
Ambivalent relationships can cause vast suffering.