MAJOR UNIPOLAR DEPRESSION: AN OVERVIEW--论文代写范文精选

抑郁症的面临的挑战是调和，理论上最连贯和实证支持假说轻微抑郁症是心理痛苦假说。而身体疼痛会通知个人,他们遭受身体伤害,激励他们停止活动,否则将加剧这种伤害。下面的essay代写范文进行讲述。

Abstract
The two major classification systems of psychiatric disorders, ICD-10 and DSM-IV, both recognize that in typical depressive episodes, the individual suffers from depressed or sad mood, loss of interest and enjoyment, reduced energy, and diminished activity. This suite of emotions and behaviors has been observed in virtually all human societies (Patel 2001).2 Table 6.1 provides an overview of the symptoms and their hypothesized functions (note: bipolar depression will not be discussed).

Any theoretical explanation of depression must account for the following characteristics of depression: low mood and loss of interest in virtually all activities, a significant reduction in productivity, suicidality, a possible negative impact on health, a cross-culturally robust 2:1 female bias, a relatively high worldwide annual prevalence rate of around 5–10% (WHO 2001; rates vary widely by country), the substantial evidence that depression is closely associated with chronic activation of the hypothalamic-pituitary-adrenal axis (HPA) (e.g, Nemeroff 1996) — which prepares the body for fight-or-flight — and the fact that the most significant known cause is a major, negative life event. More on each of these below.

LIMITATIONS OR PROBLEMS WITH PREVIOUS ADAPTATIONIST HYPOTHESES FOR DEPRESSION 
The challenge for an evolutionary account of depression is to reconcile the close association of plausibly functional symptoms (e.g., sadness and loss of interest in some activities) with its many costly symptoms (e.g., suicidality). The most theoretically coherent and empirically supported hypothesis for minor depression (a much less severe form of major depression) is the “psychological pain” hypothesis (Alexander 1986; Hagen 1999; Nesse 1991; Suarez and Gallup 1985; Thornhill and Thornhill 1989; Tooby and Cosmides 1990; Watson and Andrews 2002). Whereas physical pain functions to inform individuals that they have suffered a physical injury — motivating them to cease activities that would exacerbate this injury, as well as to avoid similar future situations which would also likely result in such an injury — psychological pain informs individuals that their current social strategy or circumstance is imposing a fitness cost, motivating them to cease activities that would exacerbate this cost, as well as to avoid similar future situations which would also likely result in a fitness cost. 

Such circumstances include, e.g., the death of children and relatives, loss of status, loss of a mate. The “social competition” or “social yielding” hypothesis similarly proposes that short-term depression is an adaptation to force the loser of a social conflict involving status or rank (a) to stop competing with the winner, (b) to accept the fact that s/he has lost, and (c) to signal submission, thereby avoiding further conflict with the winner (Price et al. 1994). The “yielding” hypothesis obviously has much in common with the “psychic pain” hypothesis and is probably best considered an important, special case of the latter — loss of a social competition is certainly a prime example of a social circumstance that imposes a fitness cost, and the pain of depression could quite plausibly motivate losers to cease competing, thus avoiding the costs of continuing a futile competition. The yielding hypothesis cannot be a complete explanation for even minor depression, however, because loss of a social competition is not its only cause — having a baby with temperament problems (C.T. Beck 1996) is but one well-documented cause of depression that does not involve losing a status competition.

Neither the yielding hypothesis nor the psychic pain hypothesis accounts for major depression, and comments by proponents of these theories suggest that they are not intended to. Losers of social competitions should yield quickly, so proponents of the yielding hypothesis (Price et al. 1994) logically argue (from their perspective) that severe and prolonged depression is maladaptive (a major depressive episode can typically persist for months). Similarly, Nesse (1999, p. 356), a proponent of the psychic pain hypothesis, suggests that “sadness is almost certainly adaptive, but depression may arise from dysregulated sadness or from an entirely separate mechanism.” A pronounced and sustained loss of interest and enjoyment in virtually all activities, loss of energy, and diminished activity are core features of major depression. Some psychic pain theorists (Tooby and Cosmides 1990, 2000; Nesse 2000) have cogently argued that, in the face of a major social failure, one should take pause. Immediately pursuing another social strategy without first evaluating the recent failure would likely only lead to another, costly failure. 

A distinction must be made, however, between a short-term reluctance to pursue one’s social strategies, which often would have been wise in such circumstances, and long-term reduced self-care, which does not improve analysis of social failures or ability to unilaterally respond to social opportunities. Except when faced with an immediate threat, individuals simply analyzing a social failure should never stop eating, bathing, and grooming; individuals who did so in the EEA would have found that their health deteriorated rapidly, with (under this hypothesis) no compensating benefits. Not only does depression have a significant, long-term negative impact on productivity, there is, as will be briefly discussed below, legitimate concern that the lack of self care accompanying depression may cause increased mortality, even in populations with ready access to resources and sophisticated medical care. Suicidality is also a very common symptom of major depression, yet there is no reason for an individual who has suffered a severe fitness cost, such as losing a social competition, to contemplate imposing additional costs on herself — especially the ultimate cost of death.

Energy conservation is another commonly proposed function for depression (e.g., A. Beck 1996). Although energy conservation was certainly an important reproductive problem in the EEA, depression does not show evidence of having been well designed by natural selection to solve it. Depression has some features that would reduce energy consumption, such as psychomotor retardation, but it has many features that have nothing to do with energy conservation, such as the intensely negative emotions that are the hallmark of depression. Neither fatigue nor sleep, two recognized energy-conserving adaptations, are associated with such intensely negative emotions in nondepressed individuals. Similarly, why would depression often be associated with loss of appetite when food is available? If it were an adaptation to resource-poor conditions, the opposite should always be the case. Why would depression be associated with insomnia, intense social rumination, or psychomotor agitation, which increase energy consumption? Why would it often be associated with feelings of guilt or anxiety? In sum, the symptoms of depression would have added nothing to, and would often have subtracted much from, the efficacy of fatigue and sleep as energy-conserving adaptations.

Conclusion
A common and reasonably compelling hypothesis is that depression is an evolved signal of social need (Lewis 1934; Henderson 1974). Many human emotions are closely associated with facial expressions and other types of signaling such as laughing and crying. Could the symptoms of depression, including suicide threats, simply be costly and therefore credible signals of need? However theoretically attractive this hypothesis, it is not supported by the evidence. Research has clearly shown that individuals react negatively to people who are depressed or exhibit symptoms of depression (Segrin and Dillard 1992), precisely opposite the desired reaction if depression were merely a generic signal of social need.3 In general, the symptoms of major depression seem designed to prevent the acquisition of benefits. Amarked loss of interest in virtually all activities, significant weight loss, psychomotor disturbances, fatigue or loss of energy, and suicidal ideation would all have impeded ancestral humans from engaging in critical, beneficial activities, such as food gathering and consumption, buffering food shortages, personal hygiene, avoiding environmental hazards, information gathering, helping relatives and friends, etc. An adaptationist account of major depression must incorporate, not avoid or reinterpret, its costly symptoms.

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