actually Depression is caused more by toxins or foreign invaders such as viruses.
it is then causative of how people perceive the ill person, which in turns becomes a situation depression. Depression is caused not by itself regardless, but you'd be surprised at how many are infected with some agent of some sort, mainly through vaccines and environment, but many viruses also play a role.
one does not simply become depressed. there is always a reason.
i know plenty of people who have lived a life of BS growing up and they are the most fun loving people I know. I know just the opposite too...many growing up in nice fun loving families and have them turn out to be the worst person mentally or physically.