"depression" is a big word behind which dozens if not hundreds of causes hide.

It's like "headache", maybe you took too much coffee today, or maybe you have stage IV brain cancer

I think that the fact that our society was mainly designed (or evolved) to maximize the profits of the people in power as opposed to peoples wellbeing plays a huge part in depression. Some people just don't fit in our monoculture (school, job, family etc) and all we are offering them are ways to make them fit and become productive members of society which was the problem to begin with..

Part of it (all of it?) SEEMS to be a lack of purpose/meaning and connection to nature. Total anecdata from my own friends/family that are/were depressed including myself.

Pet hypothesis: it is the natural response of the human mind to a unresolvable and conflict between it's world model and its experiential data. This leads to a lot of problems, because we are reluctant to act on predictions made by a known incorrect model. It is very unpleasant in the same way the pain of a broken leg is unpleasant, and for roughly the same reason. Sometimes we double down on the obviously broken model, insisting that reality change instead, which often leads to anger and violence. Other times we simply give up and seek to end the discomfort by medical or suicidal means instead. Ideally, we are able to incorporate the data into a new world model that better reflects reality and that we can make decisions with in confidence.

We go through a bunch of these during our lives, especially as children and adolescents, but society and culture have incorporated mechanisms to help young minds build new, more accurate, world models so it usually isn't much of a problem. However, we're at a point in our societal development where more and more minds are seeing the failures of their world model that society has no answer for.

The "Chemical Imbalance" hypothesis is extremely simplistic and seems very appealing to believe amongst the HN crowd. Unfortunately the evidence for it has been sorely lacking and within the past couple of decades more psychologists have been advocating for a wholistic understanding of mental illness. That is it has causes which are complex. It is a mix of childhood experiences, relationships, maladapted development and many other individual circumstances.

Read more here: https://blogs.scientificamerican.com/mind-guest-blog/why-we-...

Genetics, behavioral and thinking patterns, lifestyle, life circumstances, ...

It is part of the fight-flight-freeze response. In humans, it can be triggered by abstract thoughts, and not just from predators. It can go all the way from mild depression to full catatonic states.

Many of the replies to this think I was making a flippant comment. To clarify, like many people I take antidepressants and I find they do help me get on with things. If someone says depression isn't about brain chemistry I'm wondering what else is there? Isn't our mood a physical chemical system? If not, what else do you think it is?

I wonder if it's related to the broader trend of lowered resting metabolic rate in humans. Not necessarily that the latter causes the former, but that some mechanism is driving both: an adaptation that tells the organism that it's time to hunker down, avoid unnecessary activity/risk, and save up calories.

Might be a software issue, not a hardware issue