Please, don't go blaming the environment. If you only live to be 25, course you don't get cancer. And even if you did, you wouldn't die of it. You would get weaker and some animal would kill you, or you'd simply starve. And even if you'd die, we are probably not to know, unless you dropped into a glacier (concerning cancer couple of million years ago).
Cancer isn't one of the vices of civilization, it's a virtue. Nowadays, civilized people live long enough to even get it. Not that I want cancer, or want anyone else to have it and I know it's a bastard. But I'd rather be 80 and die from cancer than 13 and die during childbirth.
And about depression in the millennia past, or in very "savage" parts of Africa, well of course there wasn't much of it. I don't think that evolution favours BP or Depression. Only behaviour that enhances procreation in an individual will be an asset in the evolutionary battle. Even if "mad" people were reverred as spiritual leaders/seers etc. did they produce more offspring? I doubt it. In many cultures religious rank was "used" as a way of removing individuals from the genepool (or why else should so many religions require chastity )
I believe manic depression has nothing whatsoever to do with evolution but with culture. If you are constantly fearing for your survival (and tigers, famine and the rash you discovered on your privates, some centuries before medicine was even discovered), you do not ask questions. You don't go, yes there is a tiger but do I really want to run, what do I want to run for, is it all really worth it, should I just run to run again for the rest of my life - you just run. Period. Now if there is no tiger, you are plump and rosy with a full freezer, a doctor takes care of every pimple on your arse, there's a roof over your head and you don't have a worry in the world, than you've got time to ask questions.
Douglas Adams puts it this way:
The history of every major galactic civilization tends to pass through three distinct and recognizable phases, those of Survival, Inquiry, and Sophistication, otherwise known as the How, Why, and Where phases. For instance, the first phase is characterized by the question “How can we eat?” the second by “Why do we eat?” and the third by “Where shall we have lunch?”.
We have passed them all and our question is "Do we really want to eat?"
In groups were starving is still a real thread, there are very few anorexics. Funnily the countries with the most fatties (e.g. America, UK, Germany) are also the countries with most anorexia. Just like those people who have the least to worry about, worry the most. If your life is on the brink, you don't think, you act.
So probably thinking makes depressed and in that way madness is a step to a higher plane of enlightenment and human development.
