Depression: Flesh and Blood Or Thoughts and Emotions?

Is depression caused by external factors, or by our own mind and body?
The answer may not be as simple as some would like to believe. The commonly held view is that depression is caused by negative events or circumstances that result in fear, sadness, apprehension, and worry. External factors such as gloomy weather, the six o'clock news, and even how one views society at large --- are also considered major sources of depression.
Another school of thought in this issue about depression is rooted in biology and biochemistry. Going by this theory, depression is supposedly caused by chemical imbalances which, in turn, affect a person's psychological and emotional equilibrium. The discipline of psychology, however, takes a different tack by claiming that the chemical changes are effects of the psychological condition, not the other way around.
There are reports and studies that show depression as being linked to a variety of chemical changes in the brain. Changes in the brain's chemical receptors have been mentioned as possible causes of depression. The same has been said of damage to the nerves and biochemical transmitters that do the gritty work of the central nervous system. Serotonin is usually mentioned, though other neural receptors have also been named by a variety of studies into the topic. Noradrenaline and dopamine levels have also been mentioned by some studies as being linked to depression. It is these drugs that most antidepressant medications are designed to target. The basic idea is that low levels of the aforementioned chemicals causes depression, so higher levels should be uplifting. While most cases of depression are treated successfully in this manner, there are still some issues to be resolved. The low levels may be indicative of another problem, rather than being the root of the problem itself.
Psychology may be a major factor in depression, if not the root cause. Studies show that people who have suffered emotional or psychological trauma are more likely to develop depression later on in life. This is particularly true if the trauma occurred during the person's formative years, or was caused by a trusted figure in their life. Pessimism can also make it easier for a person to slide into depression, but most do not see it as a major factor. Anxiety disorders may also lead to depression, according to some studies. This stems from the negative self-perception that can be caused by anxiety disorders that cripple a person's ability to fulfill his perceived duties. These can include social anxiety and performance anxiety, among other types of anxiety disorders. As the negative self-perception sinks in, it begins to alter the person's view of reality. Eventually, as depression sets in, everything appears bleak and hopeless.
For the time being, it is difficult to be sure whether depression is a mental condition or a biological one. There is ample evidence to show that there are factors on both sides of the argument. However, there is a lack of evidence to point to either side of the coin being the definitive answer. More research into the matter is going to be needed, especially since there are some unanswered questions about depression. For example, the fact that depression seems to manifest frequently in families suggest some sort of genetic connection. Also, if the state of mind does have an effect on depression, then would there be a statistical correlation between nihilism and depression? Clearly, there is still much to be discovered about this condition.