Depression - Evolutionary factors

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From the evolutionary standpoint, major depression might be expected to reduce an individual's ability to reproduce. Some evolutionary explanations for the apparent contradiction between biopsychosocial, psychological and psychosocial hypotheses and the high heritability and prevalence of depression are explained by the proposal that certain components of depression are adaptations such as the mechanisms underlying behaviors relating to attachment and social rank. Evolutionary theorists view the condition as an adaptation to regulate relationships or resources, although it may be unwanted or disordered in modern environments. From this perspective, depression can be seen as "a species-wide evolved suite of emotional programmes that are mostly activated by a perception, almost always over-negative, of a major decline in personal usefulness, that can sometimes be linked to guilt, shame or perceived rejection". Like an ageing hunter in our foraging past, an alienated member of today's society may feel and act in ways that prompt support from friends and kin. Additionally, in a manner analogous to that in which physical pain has evolved to hinder actions that may cause further injury, "psychic misery" may have evolved to prevent hasty and maladaptive reactions to distressing situations. These insights may be helpful in counseling therapy.

• Evolutionary biological hypotheses of depression – Evolutionary analyses usually consider possible functions for depressed mood as well as clinical depression.^{[How to reference and link to summary or text]}

• Psychic pain hypothesis of depression: psychic pain, such as depression, is analogous to physical pain. The function of physical pain is to inform the organism that it is suffering damage, to motivate it to withdraw from the source of damage, and to learn to avoid such damage-causing circumstances in the future. Analogously, depression informs the sufferer that current circumstances, such as the loss of a mate, are imposing a threat to biological fitness, it motivates the sufferer to cease activities that led to the costly situation, if possible, and it causes him or her to learn to avoid similar circumstances in the future. Proponents of this view tend to focus on low mood, and regard clinical depression as a dysfunctional extreme of low mood. See, e.g., Nesse 2000 and Keller and Nesse 2005; see also Hagen and Barrett n.d..

• Rank theory: If an individual is involved in a lengthy fight for dominance in a social group and is clearly losing, depression causes the individual to back down and accept the submissive role. In doing so, the individual is protected from unnecessary harm. In this way, depression helps maintain a social hierarchy. This theory is a special case of a more general theory derived from the psychic pain hypothesis: that the cognitive response that produces modern-day depression evolved as a mechanism that allows people to assess whether they are in pursuit of an unreachable goal, and if they are, to motivate them to desist. See, e.g., Nesse 2000.

• Honest signaling theory: When social partners have conflicts of interest, 'cheap' signals of need, such as crying, might not be believed. Biologists and economists have proposed that signals with inherent costs can credibly signal information when there are conflicts of interest. The symptoms of major depression, such as loss of interest in virtually all activities and suicidality, are inherently costly, but, as costly signaling theory requires, the costs differ for individuals in different states. For individuals who are not genuinely in need, the fitness cost of major depression is very high because it threatens the flow of fitness benefits. For individuals who are in genuine need, however, the fitness cost of major depression is low because the individual is not generating many fitness benefits. Thus, only an individual in genuine need can afford to suffer major depression. Major depression therefore serves as an honest, or credible, signal of need. See, e.g., Hagen 2003, Watson and Andrews 2002.

• Social navigation or niche change theory: The social navigation, bargaining, or niche change hypothesis [1] suggests that depression, operationally defined as a combination of prolonged anhedonia and psychomotor retardation or agitation, provides a focused sober perspective on socially imposed constraints hindering a person’s pursuit of major fitness enhancing projects. Simultaneously, publicly displayed symptoms, which reduce the depressive's ability to conduct basic life activities, serve as a social signal of need; the signal's costliness for the depressive certifies its honesty. Finally, for social partners who find it uneconomical to respond helpfully to an honest signal of need, the same depressive symptoms also have the potential to extort relevant concessions and compromises. Depression’s extortionary power comes from the fact that it retards the flow of just those goods and services such partners have come to expect from the depressive under status quo socioeconomic arrangements.

  Thus depression may be a social adaptation especially useful in motivating a variety of social partners, all at once, to help the depressive initiate major fitness-enhancing changes in their socioeconomic life. There are extraordinarily diverse circumstances under which this may become necessary in human social life, ranging from loss of rank or a key social ally which makes the current social niche uneconomic to having a set of creative new ideas about how to make a livelihood which begs for a new niche. The social navigation hypothesis emphasizes that an individual can become tightly ensnared in an overly restrictive matrix of social exchange contracts, and that this situation sometimes necessitates a radical contractual upheaval that is beyond conventional methods of negotiation. Regarding the treatment of depression, this hypothesis calls into question any assumptions by the clinician that the typical cause of depression is related to maladaptive perverted thinking processes or other purely endogenous sources. The social navigation hypothesis calls instead for a penetrating analysis of the depressive’s talents and dreams, identification of relevant social constraints (especially those with a relatively diffuse non-point source within the social network of the depressive), and practical social problem-solving therapy designed to relax those constraints enough to allow the depressive to move forward with their life under an improved set of social contracts.

• Bargaining theory: This theory is similar to the honest signaling, niche change, and social navigation theory. It basically adds one additional element to honest signaling theory. The fitness of social partners is generally correlated. When a wife suffers depression and reduces her investment in offspring, for example, the husband's fitness is also put at risk. Thus, not only do the symptoms of major depression serve as costly and therefore honest signals of need, they also compel social partners to respond to that need in order to prevent their own fitness from being reduced. See, e.g., Hagen 1999, Hagen 2003.

• Darwinian psychiatry: This "failure of model-integration" theory is focused on behavioral systems (i.e., reproduction, survival, kin-investment, reciprocation), in which individuals have a marked functional consequences due to both ultimate and proximate condition-producing causes (plural). Using the 15% Principle, it distinguishes between (and incorporates) physiological, phenotpyical, trait variational, dysfunctional algorithms, dysfunctional automatic, and adverse environmental systems, wherein individuals act adaptively, albeit suboptimally, even with dysregulation, and is then assigned a ratio to each of the manifold contributing factors, creating a profile of both proximate and ultimate causal factors for which depressive features are locked-in adaptations. Joining "evolved capacities" and "adequate functioning," it argues that many features of clinical depression are adaptive, albeit suboptimally and dysfunctionally. Using "homeostasis" as a benchmark of healthy life-strategies, depressions are regarded as minimally conservative of individual energies in which the failure to adapt, or precipitating incidents, rapid resolutions, creative capacities, physiological responses, trait variation, interpersonal conflicts, maturational disruptions, and suboptimal information-processing trigger depressive responses in individuals in order to achieve more modest goals within each of the four major behavioral systems. (Reactive depressions, or "response-to-loss" models, are a separate adaptive responses to functioning, usually transient and self-correcting.) The depressive's cost-benefit analyses are also incorporated in the final assessment, and then psychiatric treatment strategies are designed to treat all the multi-causal factors together as a holistic phenomenon through empirically-validated modalities. See,

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See also

Evolutionary factors in postpartum depression

References & Bibliography

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Key texts

Papers

• Hagen EH (2003) The bargaining model of depression. In P. Hammerstein, (ed).Genetic and Cultural Evolution of Cooperation, pp. 95-123. MIT Press.
• Nesse, R. M. (1999).Is Depression an Adaptation? Arch Gen Psychiatry. 2000;57:14-20Full text]
• Kellera,M.C. and Nesse,R.M.(2005). Is low mood an adaptation? Evidence for subtypes with symptoms that match precipitants.Journal of Affective Disorders 86 27–35Full text

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