This is exactly what you'd expect if the hypothesis that depression is an evolved adaptation for surviving no-win scenarios that can only be waited out holds.

In a scenario where a disaster has negatively affected the primary productivity of the local food web (e.g. volcano, forest fire, bolide, plague or tsunami), the groups of social species that exist in an environment are likely to engage in internal strife until the food web productivity the group subsists on has returned to normality. Phenotypes which reduce activity across the board without making any changes to their distribution of activities, just hoping for things to get better on their own, are likely the phenotypes that are most successful at surviving to reproduce within conditions of intragroup strife when these infrequent disasters occur.

If this line of reasoning bears out to correctly describe the actual selection pressures that have led to the genes for depression evolving, it follows that what we call major depressive disorder is in fact the genome seeing and carrying out false positives for needing the famine-survival strategy.

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Incidentally, I first came across the theory I'm repeating here on Steven Byrne's neuroscience blog, if you want an avenue for finding sources.

I do like evolutionary explanations for a lot of human behavior, but this one feels a little too pat to me.

Patience, "biding our time", "hunkering down", etc. are actual emotional states we can experience and recognize, and depression doesn't feel even remotely like for most people as far as I'm aware.

Also, this explanation would only really work if the entire group entered a dormant depressed state together. Otherwise, the non-depressed ones would capitalize the tribe's resource and everyone would still end up screwed. But depression doesn't seem to have that sort contagious social component. On the contrary, when someone is depressed, the immediate response by people around them is generally try to "cheer them up" or encourage them to exit that depressed state. And while the depressed person is likely conveying a whole lot of negative sentiment, most aren't actively attempting to get the people around them to be depressed too. That's the last thing most depressed people want.

There is nothing about evolutionary theory that posits that all current biological structures/functions must have a evolutionary purpose.

Only the system as a whole must carry superior fitness, not each of its individual components. Given a sufficiently complex system, its rather expected that there will be negative, or even outright destructive functions that arise. You can certainly try to find a positive reason for why cancer, disease, death during conception, etc exist, but there is a much simpler explanation.

Depression in this view, isn't something outright that was adaptively constructed, but merely a side effect of how the mind works.

Context: I dabbled in evolutionary biology at the university level, not enough for even a minor in the subject.

My understanding is the existence of selection does not necessarily mean every trait that exists right now has an evolutionary benefit. It is more coarse grained that anything that doesn’t prevent you from breeding is acceptable. Depressed people are not made infertile by their depression, so there will be a subset of depressed people (assuming depression even has a hereditary component). This doesn’t mean the trait of depression has an advantage in order to exist, it just isn’t so much of a disadvantage that it doesn’t exist.

> the hypothesis that depression is an evolved adaptation for surviving no-win scenarios that can only be waited out holds

I remember from my days studying to be an actuary that the population that can best estimate mortality odds from the gut are actually the depressed. (Most of us tend to be way too optimistic about common risks and pessimistic about uncommon ones.)

This was also used to explain mammalian postpartum depression, when the mother has to make a wretching call as to whether to keep the offspring given its health, her health and the environmental context.

This fits exactly with how depression feels to me, and appears to manifest itself in me behavior-wise, according to my partner. Def going to give this some thought. Thanks!

"Depression stops ant whorls" is my favorite quick and snappy summary.

depression, like alcoholism, is a crutch and a symptom of a deeper issue, not an independent behaviour in a vacuum.