Depression is a state of low mood and aversion to activity. A depressed person will experience or display some of the following:
- Persistent sadness, anxiety or feelings of emptiness
- Feelings of hopelessness, helplessness and/or pessimism.
- Feelings of worthlessness or guilt
- Contemplating suicide or suicide attempt
- Problems concentrating, remembering details and making decisions
- Fatigue and loss of energy
- Persistent aches, pains or digestive problems that are resistant to treatment
- Irritability or restlessness
- Insomnia, waking early, or excessive sleeping
- Overeating, or appetite loss
- Loss of interest in activities that once were pleasurable (e.g., hobbies, sex, social activities, etc.)
Depression as a defense mechanism
A number of authors have suggested that depression is an evolutionary adaptation. A low or depressed mood 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 depression is so prevalent, and why it so often strikes people during their peak reproductive years. These characteristics would be difficult to understand if depression were a dysfunction, as many psychiatrists assume.
Depression 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. Depression 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 mood 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 his/her 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 mood during the winter months, even if the availability of food is no longer determined by the weather.