I don't think there is a single cause of depression or even a single type; is bipolar depression the same as Major depression? How can dysthymia possibly be similar to depression that responds more quickly to medication? If it is only chemical, how come therapy can work as well as medication and the two, together, the best?

I believe there is depression caused by having a "lousy" life, either through happenstance or one's own accidental agency or personal failure. Chemical depression to me sounds like someone who drinks too much, liquor being a depressant.

I think there appears to be more depression these days because there's both more awareness but also because humanity and life/change is moving a bit faster than the majority can deal with; our "hull" has gotten a crack in it on deck 9 :-)