[splintercell]

I firmly believe that there are different kinds of depression. The kind of depression Christina Ricci has in 'Prozac Nation', or the author of 'Noonday Demon' has, is not the same thing, which a lot of people face on episodic level.

The kind of depression you're talking about (which you incorrectly term as 'clinical depression') is exactly how you describe it. There is no cause X, in the world which would fix it.

However, a lot of people feel depressed and their cause is different, than the cause for the first kind of depression.

The article GP linked, is talking about a theory that it's caused by body shutting down to prevent you from overinvesting in failed strategy is quite true for people feeling second kind of depression, and this may be the evolutionary reason for depression.

For the first kind of depression, I believe it's a disease caused by the depression (which has evolutionary reasons) working erratically.