>

So are you arguing that westerners are biologically more prone to depression? Specifically young people in the west? That these genes are propagating especially quickly in recent years given the massive increase in depression/anxiety?
I come from an upper-middle class family, both parents still married and happy after over 25 years, always had a roof over my head, food in my stomach, and an excess of material items beyond my needs. I have no severe traumas, never had a TBI, never been abused, and so forth. By all definitions, I should be happy without any issues, and I usually am.
My father struggles with depression. We both can understand what it’s like to feel like a literal cloud rolls in from beyond the horizon and over our heads, and like a light switch, something in our brain makes a change and it starts to rain. We are both diagnosed with major depressive disorder, so is my paternal grandfather. We all three take the same antidepressant, Wellbutrin, and have for years. The brother of my 3rd great-grandmother (so my 3rd great-uncle) shot himself in the head and killed himself when he was in his early-30s, back in the late 1800s. Depression runs in my family, there’s no question.
Both my dad and I have a mutation in our SLC6A4 gene, which is responsible for producing serotonin receptors in the brain, that causes us to produce less receptors than the average person. There are several studies that suggest a connection between this mutation and depressive disorders and OCD. The link is still not certain, though. Nonetheless I think it’s an important thing to mention. There is ongoing research to understand how genetics play into depression.
My biggest trigger for a depressive episode is stress. When I experience enough of it in a certain period of time, my brain’s response is to essentially shut down. Look up the diathesis-stress model. It theorizes that psychological disorders are a result of the interaction between predispositional vulnerabilities (genetics, trauma, etc.) and stress from life experiences. This is why while my brother or even someone unrelated to me won’t develop depression in response to X amount of stress, others like myself will.
This is a biological thing, it is real and it is observable. Depression is an incredibly complex and multi-faceted issue, and it’s not always purely genetic. But as you can see for me, I have at least two direct, and one distant relative, that experiences/experienced depression. >

Thanks so much for sharing your experience and some detailed relevant facts! I will go have a think about this. Comments like this are definitely making me think. >

I’m glad you were able to read it. I can be pretty all over the place when it comes to topics I’m passionate about, so I’m happy it went to use.
Here’s my big point: yes, the world can be depressing, but that doesn’t mean we all have depression. Yes, we all likely find things depressing, but that doesn’t debilitate the entire population as a result.
Say a loved one dies, you get sad and that’s normal. It’s a sad thing to happen and the normal response is to feel sad about it. Experiencing depression is when it falls outside that normal range of sadness, where it’s been weeks or months since the loss and you still can’t get out of bed, eat a proper meal, or leave the house. Worse yet, people dealing with depression might not need to lose a loved one to experience those things, they might lose their job, experience some sort of hardship like divorce or a car accident or other trauma, and they can’t continue to function in their daily life.
Feeling sad about sad things is normal and healthy to an extent, it’s when it consumes your very being and everything you do that it starts to resemble clinical depression. >

Depression can be purely biological, purely emotional, a mixture of the two, or the first coming as a result of long-standing emotional.  
Our brains and mood run on neurotransmitters, and there can be a genetic predisposition to be lacking in those neurotransmitters, but also since our brains work on feedback loops, it is also possible to get into a feedback loop that is difficult to get out of without the help of medication.  
Of course, you can also have situational depression, where you are legitimately sad for valid reasons.  Sometimes antidepressants can help prevent that from becoming a feedback loop.  
For example, there's biological depression - everything in life is going great, but someone don't feel great and is depressed, despite having no legitimate reason to be depressed. Therapy is going to have some benefit there, to have coping mechanisms to deal with it, but antidepressants are going to be the main treatment, because there's nothing "wrong" in your life. 
Situational depression happens when a loved one dies or a relationship you value is lost, and a person feels depressed. It's absolutely valid as depression, and therapy has a huge amount of benefit there, because it is a specific issue that you need to learn to deal/cope with. Antidepressants can help sometimes, because they help with the neurotransmitters, which are suppressed because of your mood, but therapy is the best help.
You can also have situational superimposed onto biological depression - you have depression that is controlled with medication, but something bad has happened in your life that makes it worse.  Therapy would help on top of medication adjustment in that case.  
In other words, depression is complex, multifactorial and can change through the course of the disease. >


Situational depression happens when a loved one dies or a relationship you value is lost, and a person feels depressed.

This isn't depression though and even if you probably know that, just be careful saying it without clarifying. It's perfectly normal to be depressed when a loved one dies. The problem is when that depressed state persists. People who are grieving will often have short periods of time where they are very sad and then they will also have times where they feel ok, that is a healthy response. A person who is depressed as a result of the death of a loved one will be in a depressed state for a more continuous time. That's the thing to look out for. Not am I low mood because of my grief but does it persist more than it should.  
Also to add even more complexity if everything in life is going great but you feel depressed it may be your thought patterns and behaviors that are reinforcing the way you feel. So therapy can still be very helpful and may be better than medication. I think that's why the combination is pretty consistently shown to have the best outcomes. >


This isn't depression though and even if you probably know that, just be careful saying it without clarifying

I'm under the impression that any period of depression that lasts longer than 14 days is clinical depression. Our medical system doesn't differentiate based on the reason for the depression. >


Situational depression happens when a loved one dies or a relationship you value is lost, and a person feels depressed

You are correct but that's not what was stated. Also that's 14 days of depression not 14 days where during some short periods you felt depressed.
to be more clear here is some diagnostic criteria. To be depressed you would show 5 of the following with at least 1 of them being the first two over a 14 day period:

Depressed mood most of the day, nearly every day.
Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day.
Significant weight loss when not dieting or weight gain, or decrease or increase in appetite nearly every day.
A slowing down of thought and a reduction of physical movement (observable by others, not merely subjective feelings of restlessness or being slowed down).
Fatigue or loss of energy nearly every day.
Feelings of worthlessness or excessive or inappropriate guilt nearly every day.
Diminished ability to think or concentrate, or indecisiveness, nearly every day.
Recurrent thoughts of death, recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide. >

I didn't specify a time frame, and was meaning to imply it would be longer standing. But there are absolutely situations that can cause you to be depressed, clinically, if you do not have the coping skills to handle it >

I just wanted to clarify because some people mistake regular grief and being in a depressed state for depression. It did seem like you probably knew that and were referring to when people sink into a depression from their grief but I just wanted to clarify for people reading. >

So it's important we use the correct language here. 
Sad, depressed, and depression disorder, are different things. 
Being sad is an emotion. Being depressed or suffering depression are overarching feelings. Having depression disorded is a biological thing. 
The way I like to think about it is in weather terms. Being sad is like having a day where it rains. Being depressed is like there is a monsoon or hurricane. The rain doesn't last just a few hours/ a day, but multiple days. Depression disorder is like the rainforest. It rains every day and and getting sunny weather is very difficult because the trees block it out. 
Furthermore, just because someone is feeling depressed but is not diagnosed with depression disorder does not make their depression any less valid. Depression disorder however is a real biological problem. It is a chemical imbalence. 
You can also develop this chemical imbalence, so if youre depresed but not crossing the line to full blown depression disorder, you can develop that imbalence and get full blow depression disorder. 
For psychologists and doctors this disticntion is important . But for the general public it doesnt matter nearly at all and we should try to treat everyone with as much love and respect as possible at all times, regardless if they are just sad, depressed or have the disorder. >

Very true. I have experienced both kinds of “depression”, and multiple doctors agree. What you said about how someone can develop that chemical imbalance is important, though. I have decided that genetic predispositions and physical abnormalities are definitely mechanisms involved in depression, which is a wholly physical phenomenon - but I’m not convinced that the core issue isn’t sociological. I came up with a random analogy in a response to another comment about an imaginary society that lifts heavy objects all day, in which some people have a predisposition to weaker bones. >

Sure, if people in that fake society didn't lift rocks people with weak bones wouldnt be at as much as a disadvantage. 
There is definetly some merit to what you are saying, but to paint with a braod brush and say all depression is socialogical I don't agree with. Maybe a lot but definetly not all. 
Depression isn't always about being just sad, but it can be lethargy or not being able to be happy. Like not being sad but just not being able to acheive the  highs of life if that makes sense. 
There might be nothing sociological going on, no peer pressure, no social issues, no romantic issues. The person might just not feel happy. 
But all these issues regarding mental health all go hand in hand. There is no problem on the earth that is simple enough to not have 1000 aterisks attached to it and interactions with hundreds of other factors. 
So while I disagree to the notion the core issue is sociological, I can agree that that might be one of the largest contributing factors. >

I think I actually agree with this entire comment. Some of my previous wording has been misleading. What is written after your last comma is the crucial position I hold that most people here seem to reject. >

From your wording in your post it seemed like you thought all depression was a consequence on social issues, and myself and presumably others rejected that idea. 
The important thing is that there is no one qualifier, and by saying depressions core issue is sociological it may put up a barrier on entry for those who suffer deppression with no social problems. Because they would not meet that qualification of "all depression is caused by social issues" 
Thats what I came here to argue against, but it seems you donrt hold the that veiw I had thought.
I think if you reword your thought and focus more on the symptoms of the person and less of  the causes people will be  far more agreeable >

and it's good to acknowledge that both physical and social causes of depression can co-occur and reinforce each other. take having ADHD for example, I wasn't diagnosed until my 20s and had already been treating depression for 10 years. i believe I will deal with depression for life, it just seems the way my brain works. but the social consequences of having ADHD, especially undiagnosed during developmental years, are likely a major factor in why I remain depressed despite different courses of treatment and lifestyle changes >

One needs to be careful not to over-things like heritability estimates, though (and for MDD these are also rather lower than for BIP, in the order of 40-50% as I recall). 
That a disorder is heritable doesn’t mean all that heritable component is mediated by biological defects of some kind (and of course conversely, parts of the non-heritable component could still be based in biology). Heritability, ultimately, is just the proportion of variance in a trait or disorder in a given population that can be explained by genetic differences between people. 
As such, if for example genetic differences lead to differences in specific personality traits, and some of those personality traits make people more susceptible to MDD, that’s going to be part of the heritability of MDD. At the moment, the research just isn’t there to really say much definitively about this, that’s still a fair ways away. 
Most likely it’s going to be somewhere in the middle, clearly a lot of environmental factors contribute but there is also plenty of evidence for involvement of (defects in) various biological processes. Time will tell quite how the ratio of those two works out, though tbh that’s not really all that important a question (the insight into specific mechanism itself, that will allow for better intervention and prevention, is much more crucial). 
In this regard I would argue that OP is wrong here: we just can’t reasonably say to what extent it’s “difficult life experiences” rather than “inherent biological defect”, so it cannot validly be claimed at this point which is true for “the vast majority of cases” either way. >

You’re making good points. I think I agree with your criticism of my position. I am prematurely trying to jump to a conclusion on a couple of mysteries, one of them being the apparently relentless increases in depression in certain societies. I wonder what some of the viable explanations are? >

I think the first question to answer in that respect would be: are the rates of depression genuinely increasing, or is it just being diagnosed more? And if the latter, is that because of better accessibility of mental health care etc., is the threshold for diagnosis getting lower, something else? 
I think rates of diagnoses for other psychiatric disorders, including at least autism, have been increasing as well, which might be pertinent to answering these kinds of questions. Interestingly, at least for some of these disorders, I know that heritability estimates have increased over recent decades as well. Probably would be informative to compare different cultures/regions/segments of society that show different rates of change in (diagnosis of) depression here, that might help shed more light in what could be causing such changes, presumably there is research on that (that’s getting rather outside my own field, though). >

I’m inclined to agree that a lot of mental health issues are better understood from a sociological perspective. However, the boundary between our socialization and ourselves isn’t that thick. Let’s take the example of smoking. We don’t have an innate biological need for nicotine. But if your friends smoke and you pick it up, you will develop a physiological craving for nicotine and tobacco. Similarly, if we are socialized in ways that make us anxious or depressed that will eventually become a baseline of our physiology. 
So I think broadly we need to look at the societal reasons for depression, alienation and feelings of disconnectedness. But that doesn’t mean that we shouldn’t also provide symptomatic relief for individuals who are affected. >

Great point! >

Shit life syndrome it is called, some people are indeed depressed because of shitty situations.
But also, everything that happens biologically happens psychologically, and viceversa, there is this misconception about making a separation between the two, when in fact, humans are both biological and psychological. 
For example, if you feel stressed, you have more cortisol in your blood that signals the brain to feel stressed, and your environment might have caused that spike. Same happens with depression, low dopamine and serotonin signals the brain that we need to recover and stay inside, signaling that there is something wrong that needs time and attention to recover from it, and that might have been caused by your environment , or a disease in the body preventing normal function.
There are people that are naturally prone to depression because of how their brain are structured, a deficiency in some hormone in the body, and it’s been shown that depression can be passed through generations, if your mom suffers from depression, there is a likelihood that you’re prone to depression as well. >

You also don’t need depressed parents to be prone to depression, when your DNA was being created, some programming might have occurred that made you a depressed person, just by random chance… so yeah, nature have its ways to make us suffer unnecessarily and without a clear explanation for us to be satisfied >

I learned most  of these ideas from the book named “Behave, the biology of humans at our best and worst” by Robert Sapolsky, very good read >


How much robust evidence is there for these other biological theories?

I remember my therapist put it very succinctly. "Did you mother have OCD? Did your grandmother? Did other people in her line?" The answer was yes to all 3. "If it runs in the family how can it not be genetic?"
There are people in my family with OCD that lived on different continents. Much less raised in different households and having vastly different life experiences.
There's no doubt that the environment plays a huge role in your mental health. Very few are arguing against that. But to think that it's not heritable and that brain chemistry doesn't play a role is equally as fallacious as saying that the environment doesn't play a role. They are both critical. 
Regarding our environment. The biggest driving force for depression and anxiety is isolation. The human race has never had it more comfortable in their house. With lots of easy and cheap entertainment. As a result people socialize a lot less. But we still need that socialization and our brains "get sick" without it. >


"Did you mother have OCD? Did your grandmother? Did other people in her line?" The answer was yes to all 3. "If it runs in the family how can it not be genetic?"

Yes your therapist succinctly showed how they don't understand that correlation != causation. 
Usually it's fine to assume such things are linked, but that doesn't mean they are. Otherwise you're just stating claims and acting as if they're self evident. 
My gf thought clouds made wind because she's never seen it windy without clouds, and just linked to 2 together. The number of windy days she'd experienced is a much larger sample size to draw a causation relationship between that your 3 family members and whether something is genetically inherited. >

If physical health problems can have genetic inclinations that are inherited from parents, why is it so unreasonable to believe that genetics could also contribute to mental health problems as well? >

I don't think it's unreasonable, but behavior can have a strong effect on mental health as well and so perhaps we shouldn't draw conclusions one way or another without more evidence. For instance, the inherited OCD mentioned above could be more related to mimicking the habits of the parent rather than having a genetic basis. Or it could be partly both. >

A genetic role in the development of OCD is well-established. Given that OCD is in large part internal (and can in fact be entirely internal) I'm not sure how "mimicking habits" could result in its development. And no, OCD is not just being obsessed with neatness or cleanliness. >

OCD wasn't a great example, but I could see it being developed as a response to constantly feeling like you're under a microscope, e.g. a parent obsessing over the smallest details. That could create anxiety over similar things in anticipation that it would otherwise get noticed.
Not disputing the evidence of OCD being genetic. >

Part of the problem here might be that in English, "depression" can mean simply being in a depressed mood, or it can mean clinical depression (in my native language, there are different words for those). And those are two different things: one of those is a state of being that can be a natural response to your environment, and the other is a mental disorder. Another part of the problem is that "depression" is a pretty superficial psychological label that groups a lot of people with similar symptoms. But it might represent several different underlying conditions, and some of those might have environmental causes, and some biological causes. Psychology is still a pretty young field, and there's a lot we don't know.
OP, what you seem to be describing is being in a depressed mood. If you feel shitty because of the state of the world, because a loved one died, because you failed at something, well that's a fairly natural response to loss or adversity. It can grow to become clinical depression, but it's not inherently pathological. But a lot of depressed people don't really feel that way. They don't have particularly significant trauma or adversity in their past. They are beloved by others, but hate themselves. They have successful careers, a significant other, yet they feel miserable. They spend months or years with low mood, low energy, no motivation. In short, clinical depression can't always be linked to environmental causes.
Literature on depression is complex and kinda fractured, but it has been linked to biological factors: genetics (depression does run in families), the microbiome, inflammation, the HPA axis, kynurenine, etc. Those can also be linked to environmental triggers, but it can be difficult to isolate what causes what. >

You make an important point! Thanks.
In my experience, I can say that as a teenager, I gradually transitioned from feeling despair at the state of the world and my own life, to feeling numb, unmotivated, tired, anhedonic, fatigued, sore, and sleeping poorly. I feel my ability to understand my own emotions would fluctuate, and I would sometimes express this as “I feel depressed for no apparent reason”. >

While I'm not in any way qualified to make that determination, that does sound like you might suffer from clinical depression. In relation to your post, have you considered the possibility that the reason you see things so bleakly is because you have a biological predisposition for it? My experience is similar to yours, but obviously most people are not depressed by the state of the world, and not everyone falls into depression when confronted with loss or failure. There has to be something more, a biological underpinning to it. Research hasn't given a conclusive answer to what exactly that is (though there are interesting leads), but as someone that has done neuroscience research, trust me when I say establishing a clear relationship between biochemistry and a particular behavior in humans is fucking hard, and sometimes unrealistic. But that doesn't mean it doesn't exist. >


caused by difficult life experiences of some kind, and when those causes aren’t obvious, people incorrectly assume they have an inherent biological defect

I would say it's how an individual processes that life experience. Different people can experience the same thing and have it impact them in different ways. 
I think the issue comes in with the word defect. Different brains process things different ways. People tend to assume that other people experience and feel things the same way they do. There is no default "correct" brain though. So different people processing experiences different ways does not mean one is correct and one is defected. 
But there are people that are more pre-disposed to feeling depression or experiencing depression as a result of experiencing different things. >

I now realise I do believe in a genetic predisposition, but what I haven’t changed my mind on for now is the idea that the problem isn’t best understood as broadly sociological! Thanks for your input. >

Like with anything there is no one size fits all definition. And of course im sure there plenty of ppl with chemical imbalances. 
That being said i strongly believe that the vast majority of ppl are "depressed" because they dont have the ability some seem to   have where they can put blinders on and willingly deny the horrors unfolding all around us. If you face the terrible things in the world and are forced to admit they exist then you have to act on them or admit your an awful human.
I saw a comedian recently doing a bit about how the happy ppl are the ones who should be drugged up because the rest of us can clearly see whats happening to the world. >

I personally think that there cannot possibly a one fits all explanation and neither a one fits all solution for that phenomenon. We don't even know whether others experience it in a similar way or maybe what they call depression differs from what we experience as it.
I'd say it's most likely a combination of different factors and that these factors have different weighs varying from person to person.
When trying to find a solution, I'd always focus on the factors we can do something about ourselves. And in this regard I'd say it's our mindset. A quote that I'd heard in a different context but seems applicable to this too is: "We do not always have control on what happens to us. But we do have control on how we react to what happens to us."
To me the mindset of being in control, of being in charge and responsible for how I deal with my environment is quite empowering. I'm in charge of dealing with whatever life throws at me and I want to do a good job with that, so I can increase the pleasure I obtain from my life. I can indulge in my emotions whenever I want to and don't want to blunt them.
I cannot change biology. So it must not matter in my decision-making-process. What I can change is how I play the cards I'm dealt. >

Like everyone, I have had bad life experiences. One time, I came very close to killing myself. The rest of the times, I reacted appropriately with sadness or anger.
There was something biological going on that day that I hope never happens again. If it has never happened to you, it impossible to understand. The draw of driving into a river was almost irresistible. >

Depression is absolutely best understood sociologically. Ultimately, we’ve created a world in which, for many people, their basic social needs are going unmet. For example: a connection to the people/community/nature around you. This is the cause of depression from a macro perspective. Especially given the massive increase in depression/ anxiety in young people. 
I just want to address some of the thing I see people saying here. No, genetics does not explain this. Young people aren’t simply genetically more prone to depression. They’ve grown up in a different environment, one which makes them more likely to be depressed. The reality is that most depression in a predictable and understandable reaction to the circumstances that led up to it. >

I basically agree with you, but I do also wonder... given that this is the world we find ourselves in, are some people genetically predisposed to handle this situation better and not suffer depression as a result, or handle it worse and suffer more depression than "normal" for this situation?
In other words, I'm suggesting that while the sociological environment as a whole has drifted into something that we didn't evolve to cope with, there is likely still a biological component in terms of the effect (particularly the scale of effect) that has on people's mental well-being. >

A lot of people have pointed out to me that there are genes correlated with depression, and that having a depressed parent increases your own likelihood.
I don’t disagree - there’s a reason a human get get depressed, while a rock or a tree can’t. You have to have certain traits, and perhaps humans differ in the degree to which they possess those. But as for the idea that it’s a problem best understood from a sociological perspective, I guess one thing I’m trying to explain is why depression seems to be skyrocketing in certain countries. I guess it could be largely a physical but environmental thing too - something in our diet, or endocrine disruptors in our products? >

I would recommend a book like Lost Connections by Yohann Hari. I don’t believe it’s perfect, and as always don’t take it as gospel, but it does a decent job of looking at the major causes of depression. They do not tend towards what you referred to as physical environment, though I believe it touches on diet and exercise. Rather, as the name suggests, it is our social needs not being met. If you do not want to read a whole book I know he also has a Ted talk, and has made some podcast appearances. >

I think I saw him talk about drug addiction once - I agree his work needs to be taken with a grain of salt, for example, he seemed to subtly imply that some drugs don’t cause lethal physical dependence independently of psychological dependence - but I think his way of viewing the subject had a lot of merit. Thanks for the recommendation! >

I think there’s merit in thinking about addiction in this way as well. It’s certainly very messy. Addiction is mired in a context of depression, and isolation. It is a form of indirect self-harm and the reasons people are addicted tend to be from trauma. 
Many people are placed on pain killers like morphine while they’re in the hospital, yet do not get addicted. There is a larger story than that the drug is itself physically addictive. Why a person feels the need to use drugs tends to be the more important question. >

Approach this from the other side. Every organ has fail points. Every organ is susceptible to a variety of disease or internal malfunction. The more complicated a system is the more potential fail points there are. The brain is more complicated than any other organ by an order of magnitude. Why would you assume it's the only organ that doesn't malfunction when the odds are so much higher that it will? All processes in the body are chemical in nature. The chemical imbalance that was debunked was about the specific chemicals they thought were the problem, not the idea of a chemical imbalance. >

The fact that magnetic resonance therapy works better than placebo magnetic treatments demonstrates that depression has a physical component. >

One problem with the view I expressed in the post is that I am a physicalist, so I believe all mental phenomena are also physical phenomena. It’s all neurons. So changing the neurons will change the mental.
But what about the idea that the problem is best examined from a sociological perspective? If there were a social problem with our society, I would expect that to cause physical changes in humans, just as we see social problems causing drops in BDNF levels in fruit flies.
Thanks for your response! >

I don't disagree that our experience of mind is a phenomena of our physical brain.
Still, I think the all neurons perspective is a tad reductionist, as is a lit more than that, and we don't know how most of it works. There are hundreds of neurotransmitting compounds involved, the glia cells, and a host of other bits none of which we fully understand. 
We don't know how emergent functions of the brain work, and there are reasons to believe that some structural phenomena viewable on fMRI or other scans precede mental illness. 
Further, while all mental illness has some environmental components, we also know that genetics is highly important
 Twins studies demonstrate that two genetically identical people raised in very different social contexts still retain a base level propensity for various mental illnesses, including depression. >

Also gut bacteria (which makes up roughly 90% of all of our accumulative cell count) makes up to 95% of our entire serotonin supply, and it's quite difficult to have a decent gut biome in this day and age unless you're eating organic and natural foods. 
I feel like this one is a huge and underrated factor - you are what you eat (well 90% is anyway). >

True gut bacteria has huge influences on the brain and serotonin. But serotonin isn’t as large a factor in depression as many think, BDNF and dopamine are more significant, serotonin is more stress response. >

Well we understand every very little about depression. We don’t even know for sure that all the symptoms we call “depression” isn’t actually a group of distinct pathologies with varying causes and mechanisms behind them. To say you know at all what depression is or is caused by is at best an educated guess >

There is an absolutely ridiculous amount of research on depression, especially as a biological phenomenon. Just go through pubmed and read 100 studies on it. It’s pretty clear. Most of this research is done an animals, so there isn’t a sociological factor.
If you have a paywall on a study sci-hub exists. >

Asking CMV to ELI5 a psychiatric diagnosis? Bold move. I'll take the bait.
What do people think depression is? Some people will describe a physical thing, like genes. Others will describe it as an experience, like a feeling. And others will just simplify it by saying "it's the blues, stop overcomplicating everything." There are lots of opinions!
Depression is mostly a psychiatric label. It's really a statistical category that describes a number of observable behaviours along with some correlations between some physical and life factors loosely predicting the possibility of an individual engaging in behaviours that would indicate they have the unknown underlying condition. 
This may seem counter-intuitive. There's a lot of work in the world figuring out the causes and the mechanisms. But psychiatric labels are basically a helpful organizational system for the medical profession. It's what's used until more specifics are produced.
150 years ago absolutely none of this shit existed and you "had a fog" caused probably by either demonic possession or some kind of maladjustment in your green-to-blue-bile ratios. Now our labels are far more complex mumbo jumbo. Lets hope they're still not taking us all for a ride! >

So I think it depends on what you mean by depression. Depression is a physiological state. It can be normal, and healthy, and even beneficial. If grandma dies, depression is your bodies way of keeping you from taking out your emotions in a more volatile or harmful way, lets say drinking or fighting your emotions away.
In the same way that anxiety is often helpful, it is your body telling you that you didn't study well enough, next time prepare more. 
Now where most emotions or states turn into a disorder is when they aren't rational. If grandma died and I'm depressed for a few days or weeks, that's healthy. If I go into states of depression for no reason, that's essentially disorder level depression. 
So if we're talking about depression as a whole, or acute depression (an extended depression, with maybe longer than appropriate time) than sure I agree with you. Most is caused by an event, or a rational stimulus.
If we are talking on the actual disorder level, than it probably has more to do with biology than a stimulus.
Now I think a lot of people confuse the two, as in thinking because im depressed I have clinical depression, or because I get anxious I have social anxiety, but that doesn't mean they are the same. >

Rates of depression are highest in developed countries, not places where people are more likely to face hardship