Meta-analyses show that high scores on the personality domain neuroticism are a strong predictor for the development of<unk> s. A number of authors have also suggested that<unk> s are an evolutionary adaptation (see also evolutionary psychiatry). A low or depressed<unk>  can increase an individual's ability to cope with situations in which the effort to pursue a major goal could result in danger, loss, or wasted effort. In such situations, low motivation may give an advantage by inhibiting certain actions. This theory helps to explain why negative life incidents precede depression in around 80 percent of cases, and why they so often strike people during their peak reproductive years. These characteristics would be difficult to understand if depression were a dysfunction. A depressed<unk>  is a predictable response to certain types of life occurrences, such as loss of status, divorce, or death of a child or spouse. These are events that signal a loss of reproductive ability or potential, or that did so in humans' ancestral environment. A depressed<unk>  can be seen as an adaptive response, in the sense that it causes an individual to turn away from the earlier (and reproductively unsuccessful) modes of behavior. A depressed<unk>  is common during illnesses, such as influenza. It has been argued that this is an evolved mechanism that assists the individual in recovering by limiting their physical activity. The occurrence of low-level depression during the winter months, or seasonal affective disorder, may have been adaptive in the past, by limiting physical activity at times when food was scarce. It is argued that humans have retained the instinct to experience low<unk>  during the winter months, even if the availability of food is no longer determined by the weather. Much of what is known about the genetic influence of clinical depression is based upon research that has been done with identical twins. Identical twins have exactly the same genetic code. It has been found that when one identical twin becomes depressed the other will also develop clinical depression approximately 76% of the time. When identical twins are raised apart from each other, they will both become depressed about 67% of the time. Because both twins become depressed at such a high rate, the implication is that there is a strong genetic influence. If it happened that when one twin becomes clinically depressed the other always develops depression, then clinical depression would likely be entirely genetic. Bipolar disorder is also considered a<unk>  and it is hypothesized that it might be caused by mitochondrial dysfunction. Sex differences<unk> s, specifically stress-related<unk> s such as anxiety and depression, have been shown to have differing rates of diagnosis based on sex. In the United States, women are two times more likely than men to be diagnosed with a stress-related<unk> . Underlying these sex differences, studies have shown a dysregulation of stress-responsive neuroendocrine function causing an increase in the likelihood of developing these affective disorders. Overactivation of the hypothalamic-pituitary-adrenal (HPA) axis could provide potential insight into how these sex differences arise. Neuropeptide corticotropin-releasing factor (CRF) is released from the paraventricular nucleus (PVN) of the hypothalamus, stimulating adrenocorticotropic hormone (ACTH) release into the blood stream. From here ACTH triggers the release of glucocorticoids such as cortisol from the adrenal cortex. Cortisol, known as the main stress hormone, creates a negative feedback loop back to the hypothalamus to deactivate the stress response. When a constant stressor is present, the HPA axis remains overactivated and cortisol is constantly produced. This chronic stress is associated with sustained CRF release, resulting in the increased production of anxiety- and depressive-like behaviors and serving as a potential mechanism for differences in prevalence between men and women.
Mood disorder
Borderline personality disorder
Depression 
Diving disorders
Anxiety disorder
Menstrual disorder
Thought disorder
Psychosexual disorder