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Why Did We Evolve to Be Depressed?

It might sound counterintuitive, but depression might well have served an important evolutionary function — and although it almost certainly doesn’t feel like it, it could still be helping us now

Oversharing alert and full disclosure: I’m not going to be able to be objective about this. On the face of it, the idea that depression — harrowing, painful, numbing depression — might actually turn out to be a useful thing in our lives, seems hugely counterintuitive, not to say problematic. “Depression = helpful” might feel like a callous slap in the face to anyone actually living with it, and amounts to a screeching reverse in most people’s understanding of how mental health generally works. But as it happens, somewhere in the middle of researching this apparently paradoxical theory, something completely unrelated happened in my own life that has flipped me into crisis mode. As a result, I kind of get it. I think.

Annoying though this will doubtless be, I’m going to spare you the personal details — while looming large as a colossal, teeth-grinding injustice to me and members of my family, it won’t be that interesting to anyone else. 

So why mention it at all? 

Well, I find myself writing this in-between bouts of obsessive rumination — in my head, I’m fruitlessly replaying a situation I can do very little about over and over again; it’s like watching an endlessly spinning zoetrope of someone violently throwing up and not being able to turn away. And by sheer coincidence of timing, it’s exactly this kind of compulsive scar-scratching that lies at the heart of the evolutionary ideas I’ve just been hearing about from psychologists. It’s given me an unexpected appreciation for them which — super-subjective and unscientific though it may be — I’d like to attempt to share. Surprisingly, in more detached moments, it’s also made me feel kind of good about feeling like shit.

My present state of mind provides a useful illustration, too, of one of the big points Paul Andrews, an associate professor of evolutionary psychology at Ontario’s McMaster University, has been trying to get over to the world of clinical psychology for some time now: That we took a major misstep when we decided to classify major depression as a “disorder.” “The truth is that almost everybody’s had experience with depression,” says Andrews. “They don’t remember it all the time, but let me say this: If you’ve been dumped by somebody that you really cared about, you probably were depressed for two weeks — at least — and you probably met the formal criteria for major depressive disorder, as the DSM uses it.”

If I hadn’t been talking to Andrews a few days prior to my own trigger event, I would never have dreamt that what I’m currently experiencing might count as a clinical disorder. Nevertheless, in response to those criteria, as set out in the fifth edition of clinical psychology’s pathological bible, the Diagnostic and Statistical Manual of Mental Disorders, here goes: Depressed mood? Well, duh. Loss of pleasure in almost all activities? Sure, whatever. Significant appetite disturbance? Definitely this. Sleep disturbance? God yes. Psychomotor agitation or retardation (i.e., thoughts and movements on go-slow)? Actually, yes — much like this. Fatigue or loss of energy? Weary nod. Feelings of worthlessness? Not so much. Diminished ability to think or concentrate? Absolutely (I’m a week late in filing this article). Recurrent thoughts of death or suicidal ideation? Thankfully, no, not this.

Since only five of these symptoms (which must include at least one of the first two) sustained over a two-week period are officially needed for a positive diagnosis — high-five! — yes, I’m clinically depressed. Literally, it seems, a textbook case. While to me this would seem a gross overstatement (I’d call this turbulence, not depression), psychiatric tick-box orthodoxy would apparently have it that something has gone wrong with the normal, natural functioning of my brain. Except, according to Andrews, the exact opposite may be true.

“When it comes to depression,” he says, “the current diagnostic criteria pathologize normal emotional experiences.” Right. And the reason he thinks this is because of his outside perspective as an evolutionary psychologist, and some very good questions his work raises. In my own clunky formulation, these would be: If depression really is a malfunction that only serves to inflict damage — an undesirable dent in the mental makeup of our species — then how did it survive countless millennia of panel beating by natural selection? 

And, since evolutionary trends usually work to drive out the injurious traits that limit our survival chances and promote those that help us pass on genes to future generations, isn’t it more likely that a near-universal phenomenon like this one has in some way been helpful to us?

If it seems trivializing, or perhaps in poor taste, to paint such horrendous misery in a positive light, Andrews is quick to point out that, as someone who’s experienced severe depression himself, “it’s not like I disbelieve in depressive disorder.” He doesn’t deny it’s something we should seek to avoid. Rather than “disorder,” though, he prefers to describe it as “a painful common condition.” He also warns that it’s only certain types of depression that his research so far indicates can clearly be seen as adaptations (that is, traits that evolved to do something useful in the service of passing on genes). 

He’s not necessarily talking about episodes of manic (bipolar) depression, for instance; instead, his research has focused on the spectrum of dejection that’s characterized by dwelling on awful outcomes, disappointments, your own shortcomings or generally bad situations. “This ruminative depression is one of the most common,” he explains. “You could also refer to it as ‘melancholic depression.’”   

Despair, Prepare, Repair

It’s this clawing, self-flagellating habit of thought, so familiar to so many who’ve gone through a major upset in their lives, that holds the key to understanding how depression might be a feature, not a bug, in our evolved programming. Back in 2009, Andrews’s paper (co-authored with J. Anderson Thomson), “The Bright Side of Being Blue,” was published in the journal Psychological Review, presenting his argument that depressive rumination is in fact a type of cognitive processing that helps us analyze complex problems.

To me, he explains this in terms of the two-speed model of mental processing, widely researched by psychologists and behavioral scientists and popularized by Daniel Kahneman’s 2011 global bestseller Thinking, Fast and Slow. To vastly (and heuristically) summarize this influential cognitive model: Kahneman and others hold that humans parse the world around them in one of two ways. We decide our actions on the basis of either a quick, intuitive thinking style (“Type 1”) — which employs clever shortcuts, involves sparky assumptions and allows us to make blisteringly efficient use of our mental resources, but is also prone to misleading biases and errors of judgement — or a much slower, more deliberate mode of thought (“Type 2”), which uses methodical, logical, stepwise reasoning to work through tricky problems. 

“Basically, lots of other researchers way before me have noted that sad, depressed mood promotes a slow, careful, methodical, analytical processing style,” says Andrews, and he thinks depressive rumination is a kind of automated version of Type 2 analysis, which our brains resort to in certain kinds of emotional emergencies.

He points out that the big drawback of analytical thought — both for modern humans and in our ancestral past — is that it demands an awful lot more from us than the quick-fire, Type 1 response to problems: “This Type 2 processing style is time-consuming, attentionally demanding and energetically expensive. Which means organisms need to be motivated in order to engage in it.”

For our distant ancestors, rapid, intuitive thought would have obviously come in handy — hunting, gathering, avoiding predators and sizing up suitable mates are all things that benefit from lightning decision-making. The question is, could there have also been situations where you or your offspring would have obtained a survival advantage through dwelling on intractable problems for hours on end? (With all the Paleolithic downsides that might entail: Social withdrawal from grooming rituals; not touching your haunch of mammoth; no longer getting any joy out of killing things with sharpened sticks…) Andrews believes that there would have been, and they would have been just those sort of circumstances that begin with an extreme emotional event — the loss of a loved one, say, or social ostracization, or some thwarted desire. “Now what we’re doing is linking an emotional state — sad, depressed mood — to the Type 2 processing, as its motivator.”

It’s an abstract idea, and to illustrate it he offers a more relatable modern example. Think of a physician, he says, who makes some sort of dreadful mistake, inflicting serious harm on a patient. “You can easily see how they might get anxious and depressed over this incident,” he says. “They’re depressed they hurt their patient, but they’re also potentially worried about how they may have harmed their own careers, their reputations amongst their peers, lawsuits, etc. There’s a lot there to get depressed and anxious about.” 

Cue Type 2 rumination on repeat. With this process engaged, says Andrews, and the awful mistake never far from their minds, “the other thing that happens is that they make productive changes to their practice. Things like: They read their patients’ charts more carefully; they write and document what they’ve done with more detail; they’re less reliant on other people to get information about patients; they double-check everything; they may read more medical literature, in order to understand what they should have done; they also are more likely to consult with colleagues who are more experienced.”

You get the idea. Essentially, a by-product of their fixation on the bad thing that happened, is that similar mistakes become less likely in future — while overall better outcomes, for themselves and their patients, also become more likely. What Andrews is saying is that perhaps this chance of better outcomes isn’t so much a by-product of depressive rumination after all, but rather the product. The reason we’ve retained our propensity for despair is that — averaged out across the species and down the millennia — its presence is genuinely productive and has a net-positive effect in our lives. “Now,” he says, “the next thing to ask is: What’s the relation between the misery that they feel and the productive changes? And the answer to that is that it’s a nice, strong, positive relationship. The more misery they feel, the more they’re going to make productive changes to their practice.”

When it comes to harmful events in general, “mistakes, failures, losses,” he argues, “The idea would be that the basic function or value of depression is to help you avoid a recurrence of these things. So it could be you’ve lost one child, but in an ancestral condition you’re likely to have five more kids, so thinking about why this child died may help you reduce the risk that future children die. It could be that your partner is cheating on you, and by understanding why she or he is cheating on you, and what you might have done differently, you might be able to prevent future cheatings.” 

The key thing to appreciate in all of these examples is that “the depressed mind is going through the causal chain of events and trying to map out all of the causes that led to the harmful events — whether it’s a mistake, a failure or a loss.”

Or, in my own case, a mistake made by someone else. 

How does this stack up against my live, subjective example? Writing all of this right now from the bottom of a ruminative well (and noting, of course, that I may well have been hopelessly primed by my prior conversation with Andrews), I have to say: Yep, it does kind of stack. It might not look like progress, but each time I return to the problem it feels like subtle adjustments in my interpretation of events are being made in the background. It’s at least plausible there’s some incremental problem-solving algorithm whirring away back there that I’m too self-absorbed to register. 

Who knows, though? 

With other mental processes that definitely are adaptations — sleep, say, or dreaming — it’s not like I’m in any way able to feel or fathom the work they’re doing on my behalf.

The bigger, more gaugeable point, about how this experience might make me more alert to the risks of a similar sideswipe down the road and nudge future-me’s behavior toward tempering those risks: Hell yes, absolutely — I can totally see that, and in all sorts of ways. I’m a bit old to have a formative experience, but this feels like it might be one.

If the kinds of depressive interlude Andrews is talking about really are there to give us an edge in our lives, “It’s to promote a slow, careful, methodical type of avoidant learning,” he says. In evolutionary terms, that would be depression’s function, “in the same way that vision is the function of the eye.”

‘A Fearful Gift?’

“It’s clinicians that give rumination the bad name,” says Steven Hollon, professor of psychology at Vanderbilt University, who himself has a clinical background — and, as one of the pioneers of cognitive behavioral therapy, is among the most respected figures in the field. “If you look up ‘rumination’ in the dictionary, it talks about a careful thinking through of things,” continues Hollon. “But when you look up ‘rumination’ in a medical dictionary, it says, ‘Useless obsessive ruminating about stuff.’ So clinicians have assumed because we mostly see rumination in depressed or obsessive clients, that it’s a bad thing that’s part of the psychopathology, when people who aren’t clinicians wouldn’t necessarily take it that way. Philosophers would think it’s a very good thing.”

As Andrews points out, in general, the trope of the “brooding melancholic genius,” from Achilles to Hamlet to Beethoven to Sylvia Plath, looms large in our culture. For him, the imprint of rumination on centuries of great art presents a handy historical clue “that being melancholic actually enhances your cognitive thinking.” Arguably it fueled an entire artistic era in the Romantic movement, and in a 2018 paper they collaborated on, titled “Artists Provide a Much Needed Alternative to the Disorder Narrative of Depression,” Andrews and Hollon quote one of the age’s figurehead poets, Lord Byron, who wrote: “…the glance of melancholy is a fearful gift; what is it but the telescope of truth?” In appreciating the usefulness of depression, suggest the authors, “Science is finally beginning to catch up with artists.” 

Interestingly, when it comes to clinically diagnosed conditions, a 2011 Swedish study of 300,000 families, in which at least one member had been diagnosed with a severe mental disorder, found strong links between the creative professions and both bipolar depression and schizophrenia — though explicitly not with the kind of unipolar depression associated with sojourns into Type 2 soul-searching.

For Hollon, meanwhile, the outward differences between bipolar and unipolar depression lend added force to Andrews’s description of the latter as a normal feature of mental life. “Ten years ago I wouldn’t have believed it,” he says. When Hollon first met Andrews he was skeptical about his ideas, but felt they should be published. “I thought I was just being nice to a colleague that I’d met socially, encouraging him along with this stuff. But nevertheless, 10 years of reading, discussion, arguments — I’ve pretty much come around to his side of it.”

As a clinical researcher looking for ways of treating depression, Hollon has a different academic perspective and doesn’t agree with Andrews in every respect. But he points out that one of the things we do know about depression is that “almost all episodes end on their own. Most other disorders don’t stop on their own accord; depression does. It’s what we call ‘spontaneous remission.’” Aside from Andrews’ explanation, he says, “there’s no theory of etiology [i.e., causal explanation] that accounts for that.”

On his reading, unipolar depressive episodes seem to lack the pathological markers of a classic “disorder” when compared to other psychological conditions. Unipolar depression, for starters, is extremely widespread but not that heritable — according to the standard measure of heritability (in which a zero indicates the genes you inherit from your parents have nothing to do with you having the trait in question, while a one means genes are all that matter), unipolar depression comes in between 0.3 and 0.4, “which means it’s less heritable than political preference, as how you tend to vote has about a 0.5 heritability,” says Hollon. Bipolar disorder, on the on the other hand, has a heritability of 0.8, which means genetic factors have about the same significance as how tall you are.

“So we’ve got unipolar depression, which is incredibly common,” says Hollon. “Probably more common than we realize — about twice as common in women as in men — and with low-to-modest heritability. We’ve got bipolar depression, which is evenly divided between the genders, generally more severe when you get it and highly, highly heritable. That looks to me like something that comes closer to an operational definition of a disease. It looks like whatever the mechanism is that we have for unipolar depression, that is where it goes wrong.”

Painful Realization

Another way to look at it, says Hollon, is by analogy with physical pain. “Almost all of us have the capacity to feel pain, and for most of us, that helps us not do stupid things,” he says. “Pain is an unpleasant, distressing experience which kept our ancestors alive, keeps us alive. And I don’t consider pain a disease. I’d consider those folks who either don’t have the capacity to feel it or who have it in the absence of external stimulation — those are the ones that have the disease.”

To clarify this, he points to an unlikely source: Research from 2014 concerning squids’ efforts to avoid being eaten by sea bass. In just about the most coldly Darwinian experiment you could devise, researchers rated the survival chances of squid — who have developed sophisticated techniques for evading predators — when placed in a tank with their natural enemy, the sea bass. Some of the squids they maimed, with a range of injuries to their tentacles; some of these injuries they inflicted with anesthetic, some without. While noting that they couldn’t be sure that what the un-anesthetized squids were feeling was “pain” exactly, they could be sure that these poor animals were more alert to the presence of predators, went to extra lengths to avoid them and survived their encounters more often than their anesthetized brethren.

At the time, Edgar Walters, one of the researchers involved, commented: “This study provides the first direct evidence for the plausible evolutionary hypothesis that sensitization mechanisms — which in some animals are known to promote pain — have been shaped by strong evolutionary selection pressures.”

“The moral of the story for me,” says Hollon, “is if you’ve got a choice between doing something which anesthetizes — which is what [antidepressant] medications do — versus doing something which advances the processes that depression evolved to serve, you’re going to be better off with the latter than with the former.”

None of this is to say, of course, that we should let depression naturally run its course without interventions. In its most distressing, chronic and recurring forms it can devastate lives, and some form of diagnosed depression is thought to be implicated around half of suicides. But what it does seem to suggest is that, just like most doctors don’t routinely prescribe morphine for transient aches and pains, depressive episodes should be met in a more personalized, measured way than simply blitzing them with SSRIs.

In treating the symptoms of depression, “[Cognitive behavorial therapy] doesn’t work better than medications,” says Hollon. Where cognitive therapy does appear to have an edge over the pharmaceutical approach, though, “is it seems to have long-term, enduring effects.” It cuts risk for subsequent episodes by at least half, “and that’s one thing medications can’t do.” 

Why might cognitive therapy have longer-lasting success in controlling depression? One possible answer is that medicating depressive episodes, in “driving serotonin levels in the brain up four times anything that occurs in nature,” might remove their pain while prolonging them indefinitely. In Hollon’s experience, treatment with drugs involves markedly higher relapse rates, because, he says, “The episode never runs its course; you never have the spontaneous remission. They’re not addicted in the classical sense, but it’s very hard not to have symptoms come back within a couple of months of the time they come off.”

Another answer is that cognitive therapy, in which people talk through their fixations and face up to the patterns of behavior at the roots of their distress, opens a direct line to the evolutionary purpose of the episode. “If you’d asked me 10 years ago, [I’d have said] what we’re doing is helping people stop ruminating and start thinking productively about that stuff. Now, after reading Paul’s stuff, I think what happens is we’re secretly helping people ruminate more efficiently,” says Hollon. In a paper he’s recently put forward, he also points out that cognitive therapy would “not work if patients were not capable of thinking clearly — if their ‘brains were broken.’”

If some types of depression really are adaptations, and if recognizing them as such leads to more effective, commensurate forms of treatment, are there other cognitive “flaws” worth reframing as evolved phenomena in order to address them properly? Does it help to consider implicit bias as an inbuilt survival mechanism, for example? Or any other of the DSM-defined psychiatric disorders that seem irredeemably negative but might be better explained by their hidden virtues? 

Perhaps

It’s a notoriously hazard-strewn field in which to conduct conclusive scientific research. But there’s at least one plate of calamari out there that suggests it’s worth investigating.

And to cycle back, one last time, to rumination: As I can attest from close-up, it’s horrible, can feel like drowning and has an irresistible undertow that only seems to pull you out further. But equally, that pull you feel could just be the tide going out — meaning eventually you’ll be able to walk back to shore and get on with life as before. In either case, however long my own period of preoccupation takes to pass, allowing it to wash over me feels a lot less of an exhausting prospect than trying to swim against it.

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