Depression and stress: a biopsychosocial exploration of evolved functions and mechanisms.

Depression is a common and debilitating disorder linked to social adversity and stress. There have been many theories suggesting possible evolved functions of depression but few have explored evolved defensive mechanisms for coping with stressful events and how these maybe compromised in human depression. This paper will review some of the current evolutionary theories of depression and explore how major depression can arise when evolved defences to cope with adversity (e.g., fight, flight, disengage, submit and help-seeking) are aroused but blocked, arrested or ineffective. Psychosocial stressors can be seen as both activating,but also as arresting, evolved stress-coping defences leading to chronic states of stress with physiological effects on mood. This paper is set in the context of an evolution informed biopsychosocial approach.