|Q. Is a tendency to depression inherited?
It seems there are some people whose brain chemistry is predisposed to the depressive response, and others who are at much lower risk of depression even if exposed to the same physical or psychological triggers. The genetic relations of manic-depressives are at a higher risk for unipolar depression than the population at large or their adopted/by marriage relations. There seems to be a link between high creativity and the gene for manic-depression: artists and writers often are not manic-depressive themselves, but have a family member who is. Studies of families in which members of each generation develop manic-depressive illness found that those with the illness have a somewhat different genetic make-up than those who do not get ill. However, the reverse is not true: not everybody with the genetic make-up that causes vulnerability to manic-depressive illness has the disorder. Apparently additional factors, possibly a stressful environment, are involved in its onset.
Major depression also seems to occur, generation after generation, in some families. However, depression can occur in people with no family history of any form of mental illness. And I would be reluctant to suggest that there is any human who is entirely immune to depression under all possible conditions.
Psychological triggers: many, if not most, people with depression can point to some incident or condition which they believe is responsible for their unhappiness. Of course, people with severe depression are prone to astonishingly virulent and inappropriate guilt and self-hatred.
The (genuine) life events that most often appear in connection with depression are various, but there is one distinguishing feature that appears in many cases, over and over:
loss of self-determination, of empowerment, of self-confidence.
a loss of self, of the abilities or activities that a person identifies with herself.
Stereotypically: a man loses the job that had defined him to himself and others, whether that definition was "executive" or "breadwinner"; a woman who had spent her whole life preparing for and living the role of wife, supporter, caretaker, is suddenly left alone by divorce or death. In general, any life change, often caused by events beyond one's control, which damages the structure that gave life meaning.
The ability of a person to respond to such an event will depend on many factors, including genetic predisposition, support from friends, physical health, even the weather. It can also depend on internal psychological factors which may best be explored in talk therapy: why is the person's self-esteem so bound up in the position or state that has been lost? Can she find a new source of self-esteem? Therapy can be immensely helpful here.
Obviously, not everyone to whom this sort of event happens becomes depressed, and not every person who becomes depressed has had this sort of catastrophe befall them. In fact, if a person suffers a loss and then becomes depressed, it may well be that they weathered the loss in fine style and then succumbed to a much less obvious trigger, psychological or physical. Some depressions may well be caused by a spontaneous aberration in brain chemistry, with no trigger that we can currently identify, just as a seizure or migraine may have an obvious trigger or be apparently spontaneous.
However, once the depressive state has set in, both physical and psychological problems will be generated in abundance. What faster way to lose a job or a spouse than to be too depressed to work or to communicate? What worse psychological state for coping with a blow to identity can there be than a chemically promoted, pathological self-hatred? And what can be worse for self-esteem than watching one's appearance and household disintegrate as one loses the motivation to shower, straighten up, wash dishes or laundry, or choose attractive clothes? Health deteriorates as well: some depressed people can't sleep or eat, others sleep constantly (a real help on the job!) and eat incessantly, sometimes in order to stay awake, sometimes because it's the only thing that gives a little pleasure or comfort. (Carbohydrates induce production of serotonin, so there may be an element of self-medication here); almost no one has the impulse to exercise or get fresh air and sunshine. Most if not all of these effects form feedback loops, increasing in magnitude and becoming triggers for further depression.
The question, "Is depression mostly physical or psychological," is rather beside the point. Depression may be triggered by either physical or psychological events. Most commonly, both seem to be involved, though it is often difficult to separate the two when one is talking about psychology and neurochemistry. But however it begins, depression quickly develops into a set of physical and psychological problems which feed on each other and grow. This is why a combination of physical and psychological intervention has been shown to give the best results for most patients, regardless of any classifications that doctors may have tried to impose on their depression and its cause.