I don't follow your take. If you were sick 500 years ago your survival chances were low. If you are sick today your survival chances are lower (but not as much). Why is depression any different ?

Depression must have had some survival value or it would have evolved out.

Same could be said of hunger or tiredness. In other words, depression can be an unwanted, but inevitable byproduct of our internal workings - same as being tired is.

My guess is it caused people to stay home and keep their head down when things were going badly. Which may have been functional in a violent tribal ancestral environment but maladapted for the modern world.

I disagree. Life 500 years ago was a constant struggle to stay alive. That left very little time to sit around and be depressed.

For those humans, at that time, who were mentally ill, I agree, they either died from exposure or were protected by other humans. That protection was expensive, though, and wasn't available to many families.

Why would you want to survive, though. Just for the sake of it?

Actually it feels somewhat unfair, how hard it is to die, nowadays. You literally have to commit a violent act towards your body to do it.

I'd love to just sort of blamelessly die by exposure or something. No fault of mine and no fucking life on Earth, thank you very much.