Disturbed by the continuing and uncritical darwinization of psychiatry, especially the tendency of psychiatrists to explain mental illnesses as evolutionary adaptations, I’ve written a piece for the Psychiatric Times, which I’m told is the most widely read publication in the field. You’ll have to register (free) to see it at the journal, but I’ve posted it in its entirety below.
This article grew out of two of my posts on this website from last August (here and here). I felt especially compelled to write it because the authors of the study I critique think that the if depression is an evolved adaptation, psychiatrists should treat it with Darwinian remedies. To them, this means using problem-solving talk therapies (not necessarily a bad thing, I guess, though I don’t see why this should always be the best approach), and, especially, withholding medication. If depression is adaptive, so they say, then people should be encouraged to suffer through its pain to receive its benefits.
The Evolutionary Calculus
The discipline of evolutionary psychology views modern human behaviors as products of natural selection that acted on the psychological traits of our ancestors. A subdiscipline, evolutionary psychiatry, tries to find evolutionary explanations for mental disorders.
One of the most common subjects of evolutionary psychiatry is depression. Although debilitating, depression is also reasonably widespread. Estimates of its prevalence in Western nations range between 5% and 20%, and the disorder appears to depend at least partly on an individual’s genes. The relatively high frequency of an apparently maladaptive and partially genetic syndrome has led to speculation that it may really be “adaptive” in an evolutionary sense—that is, a liability to depression may have been installed in our genome by natural selection.
A recent version of this idea is the adaptive rumination hypothesis (“ARH”) of Andrews and Thomson,1 which posits that depression evolved as a way to solve difficult and complex problems, most of them involving social interactions. Instead of being a pathology, depression is seen as a useful complex of thoughts and behaviors that enable troubled people to withdraw from the world, deliberate intensively about their social problems, and devise solutions. Andrews and Thomson suggest this behavior evolved because it was adaptive in our ancestors, and may still be so.
The ARH has attracted a good deal of attention, much of it favorable. It was, for example, the subject of a recent article in The New York Times Magazine.2 Debate about the ARH is not purely academic, for Andrews and Thomson see the idea as pointing to specific therapies, including problem-solving talk therapies and the deliberate withholding of medication. Since these suggestions stem from a specific evolutionary hypothesis, we should carefully examine that hypothesis.
I have previously discussed a number of troubling problems with the ARH.3 Andrews and Thomson deliberately conflate clinical depression and simple sadness, assuming that these are simply positions on a continuous psychological gradient. They give no evidence that depression is caused by, rather than the cause of, difficult social problems, and they fail to show that depression actually helps people solve those problems. And many of the “experiments” supporting the ARH are unrealistic, bordering on silly. One such study mimicked the effect of depression on problem solving by having people engage in mock currency trading while listening to sad music.
Rather than repeat my critique, I want to discuss how evolutionary biologists identify features as “adaptations,” and relate this to evolutionary explanations of mental disorders such as the ARH. I will show that depression does not meet the minimal requirements for qualifying as a biological adaptation, and that even if it did, the evolutionary explanation of the ARH—and of other “adaptive” theories for depression—is scientifically unsound.
The ARH is unsatisfactory for three reasons:
Depression is not an adaptation in the evolutionary sense. Andrews and Thomson consider depression an “adaptation” because it supposedly helps the sufferer solve problems. But an evolutionary adaptation is more than something that is merely useful. Biologists consider a trait adaptive only if that behavior, and the genes producing it, enhance an individual’s fitness—the average lifetime output of offspring. It is this genetic advantage, and the evolutionary changes in behavior it promotes, that is the essence of adaptation by natural selection. To demonstrate that depression is an evolved adaptation, then, we must show that it enhances reproduction.
Andrews and Thomson don’t do this, or even try. And if they did try, they probably wouldn’t succeed, for everything we know about depression suggests that rather than enhancing fitness, it reduces it. The most obvious issue is suicide, a word that, curiously, does not appear in Andrews and Thomson’s text. Statistics show that those with major depression are 20 times more likely to kill themselves than are individuals in the general population.4 Evolutionarily speaking, this is a strong selective penalty. Depression also appears to reduce libido and may make one unattractive as a sexual partner. Andrews and Thomson point out depression’s “adverse effect on women’s fertility and the outcome of pregnancy.”1,p.638 Other health problems are comorbid with depression, although it’s not clear whether depression is the cause or consequence of these problems. Finally, studies show that depressed mothers provide poorer care of their children.
If there is counterevidence that depressive rumination outweighs all these problems and enhances reproduction, Andrews and Thomson don’t provide it. The evolutionary calculus for depression—as for any psychological “adaptation”—demands an answer to this question: how does that condition affect your expected number of offspring? It is odd that evolutionary psychiatrists neither answer this question nor, with rare exceptions, consider it, especially because data on reproductive output are not hard to gather.
If the evolutionary calculus is not favorable, one can still appeal to history: while depression may not be adaptive now, maybe it was reproductively advantageous in our ancestors. Perhaps the symptoms of depression were less debilitating in the past, or there was a lower possibility of suicide. Such appeals often smack of ad hoc special pleading, especially because we’re largely ignorant of the conditions under which our ancestors lived. Andrews and Thomson try this plea:
“A design analysis does not require depressive rumination to be currently adaptive because modern and evolutionary environments may differ in important ways. . . All that is required is that on average, depressive rumination helped people analyze and solve the problems they were ruminating about in ancestral environments.”1,p.644
This is wrong. Appeals to problem solving in the past, as to the present, must ultimately involve reproduction. Note too that if depressive rumination no longer helps us solve problems, we can ignore Andrews and Thomson’s suggested therapies.
But we need to consider other data as well—data about the genetic basis of depression. And here the ARH also fails.
The ARH does not explain the existence of genetic variation for depression. No evolutionary hypothesis about depression is credible without specifying the nature of genetic variation. It is most crucial to propose whether the genes producing depression are fixed or segregating. And both hypotheses come with problems.
“Fixed” genes are those for which all individuals have identical copies, presumably because those genes produced a form of depressive rumination that was favored in all human populations. Under this scenario, individuals do not vary genetically in their liability to depression, so variation in the disorder reflects only the different environments faced by different individuals (these environments include nongenetic accidents of development).
Under the fixed-gene model it is impossible to show by pedigree analysis that there is a “genetic basis” to depression, for those methods require the existence of genetic variation among individuals. For the same reason one could not demonstrate an evolutionary advantage of genes causing depression, since everyone currently carries the same “depression genes.”
Thomson and Andrews apparently reject this model because they recognize that individuals do differ genetically in their susceptibility to depression. They thus accept the second scenario: segregating “depression genes,” in which variation among individuals results from variation in both genes and the environmental circumstances that precipitate the disorder.
But adopting the “segregating-gene” hypothesis creates other problems, for now one has to explain not only the selective advantage of depression but also why genes producing it are segregating. Genes with a uniform advantage should not show this kind of variation. And population genetics theory tells us that the biological conditions under which natural selection maintains genetic variation for a trait are quite restrictive. One requires either that heterozygotes (individuals carrying one copy of a “depression” gene and one copy of a “nondepression” gene) have a higher fitness than individuals having two identical copies of either gene, or that environments vary over time or space in a way that depression genes are favored at some times or places, and disfavored at others. And even in this latter scenario, different environments have to appear in precisely the correct frequency or spatial distribution lest a single, generally adaptive form of the gene become fixed.
Neither Andrews and Thomson—nor, as far as I know, any proponent of adaptive explanations for mental disorders—describes what form of selection they see as maintaining genetic variation. Without such a hypothesis, any adaptive theory cannot be taken seriously, much less experimentally tested.
There is no reason to think that depression is an adaptation rather than a pathology. Lacking evidence for a reproductive advantage of depression, Andrews and Thomson see the malady as an evolutionary adaptation for three other reasons: it is an “orderly” syndrome (“there is a neurological orderliness [anhedonia and biochemical effects on serotonin concentration that affects rumination] that appears to specifically and proficiently promote analysis in depressive rumination and is not likely to have evolved by chance”1,p.622); it is relatively common both within and among cultures; and it has a partial genetic basis.
None of this suggests that depression is an adaptation rather than a pathology. The “coordination” of symptoms is a post facto rationalization: with sufficient imagination, one can view nearly any mental illness as an orderly and useful syndrome. Schizophrenia, for example, could be considered a cluster of “coordinated” symptoms that enable individuals to discard a reality that is simply too painful to bear. Without information that depression enhances reproduction, the idea of adaptive “coordination” is mere storytelling.
More importantly, there are alternative explanations for disorders that are fairly common and have some genetic underpinning. Take alcoholism, which has an incidence similar to that of depression (about 7%), and appears to have some genetic basis. But nobody maintains that alcoholism is adaptive. Rather, it’s almost certainly a pathological effect of an environmental change (the discovery of fermentation and distillation) on an adaptive trait (the evolved wiring and pleasure centers of our brain). Like the painful and sometimes fatal childbirth that is the byproduct of selection for larger human brains, depression could simply be a maladaptive byproduct of a feature that is generally adaptive—perhaps the wiring of those brains. Viewed in this way, depression could be a “spandrel,” a genetic hitchhiker that is a byproduct of something else.5
Alternatively, genes that cause depression might have some advantage when they are present but do not produce the disorder. This can happen if the condition has what geneticists call “variable penetrance”: 10% of individuals carrying the dominant gene for retinoblastoma, for instance, don’t develop the disease. Or, genes that cause depression only when present in two copies could, when present in heterozygous (one-copy) condition, have another, unknown advantage. Note that these two scenarios offer an adaptive explanation for depression genes that do not view the condition itself as adaptive. And both can be tested, for they predict that the non-depressed relatives of depressives (who carry but don’t express “depression genes”) should have higher reproductive output than do non-depressed people whose relatives are also not depressed.
This critique of the ARH applies, of course, to other adaptive explanations of depression, including the plea for help theory,6 the social rank theory,7 and the depressive realism theory.8 Further, some have suggested that depression is adaptive because it and other affective disorders are associated with high creativity.9 This suggestion is also dubious, as there is no evidence that depressed people who are creative have a higher reproductive output than other members of the population.
Andrews and Thomson conclude that, in view of the ARH, problem-solving therapies like cognitive behavioral therapy are the go-to treatments for depression. Further, they say, doctors should not be too hasty in prescribing antidepressant medication because the afflicted should be willing to “endure the pain”1,p.645 in hopes of a more permanent, evolution-based cure. Indeed, one could read the ARH as suggesting that depression should not be cured, but cultivated!
But Andrews and Thomson’s prescriptions lose force to the extent that they rest on a flawed biological premise. Of course researchers should continue to compare talk therapies and to determine which, if any, drugs are useful in alleviating depression. But in the meantime, let’s not expropriate and distort evolutionary theory in a misguided attempt to claim mental disorders as “adaptations.”
1. Andrews PW Thomson JA Jr. The bright side of being blue: depression as an adaptation for analyzing complex problems. Psychol Rev. 2009;116:620-654.
2. Lehrer J. Depression’s upside. New York Times, Feb. 25, 2010.
3. Coyne JA. Is depression an evolutionary adaptation? Available at: [Part 1] http://whyevolutionistrue.com/2009/08/29/is-depression-an-evolutionary-adaptation-part-1/. [Part 2] http://whyevolutionistrue.com/2009/08/30/is-depression-an- evolutionary-adaptation-part-2/. Accessed May 25, 2010.
4. Lonnqvist JK. Suicide. In: Gelder MN, Andreasen, Lopez-Ibor J, Geddes J, eds. New Oxford Textbook of Psychiatry, 2nd ed. Oxford: Oxford University Press, 2009:951-957.
5. Pies RW. The myth of depression’s upside. Available at: http://psychcentral.com/blog/archives/2010/03/01/the-myth-of-depressions-upside/. Accessed May 25, 2010.
6. Keedwell P. How Sadness Survived: The Evolutionary Basis of Depression. Oxford: Radcliffe Publishing; 2008.
7. Gilbert P, Allan S. 1998. The role of defeat and entrapment (arrested flight) in depression: an exploration of an evolutionary view. Psychol Med. 1998;28:585-598.
8. Taylor SE. Positive Illusions: Creative Self-deception and the Healthy Mind. New York: Basic Books; 1991.
9. Andreasen NC. Creativity and mental illness: prevalence rates in writers and their first-degree relatives. Am J Psychiatry. 1987;144:1288-1292.
91 thoughts on “Is depression an adaptation?”
Good read. A minor addendum: the reproductive benefit of the family group at the sacrifice of the individual could also be considered, but of course would need to be shown and isn’t, and in that case would argue against their treatment suggestions since we can and should be less cruel than nature.
I had a thought while reading the first point which may be pertinent – namely: “Depression is not an adaptation in the evolutionary sense”. I think it could be an evolutionary adaptation, if you’ll hear me out.
Here I’m appealing to history rather than present day. What if parents carried a gene that gave their offspring a greater than average chance of being depressed and therefore also, as Andrews and Thompson suggest, better problem solvers. Not all their children would be depressed but there’s a good chance that out of 3 or 4 children one of them would be. Now, this family would live in a tribe. This tribe would face problems that perhaps the depressed person, being a deep thinker, could help solve. An alpha male could take credit for making life in the tribe better, get the woman etcetera, but the depressed person actually helped make the “fitness” of the tribe as a whole better even though their personal fitness to the gene pool is below average.
I’m no scholar, and I wish I could write my thoughts more cogently – but to me it sounds plausible.
I have two problems here:
1) There’s no evidence that people who are depressed are actually better in any way at solving problems, social or otherwise. In fact, the opposite seems to be the case.
2) One of the characteristics of depression (if I’m not mistaken) is a complete lack of motivation, to do anything. This would include actually solving their problems, or thinking about them. Depression doesn’t seem to lead to helpful ruminations.
From this, that claim is fairly specious.
To me, it seems more reasonable that depression is simply an overload of existing natural emotional mechanisms and reactions to stress. At the point of real depression, the person is so overwhelmed by these reactions that they simply can’t muster the mental or physical effort to shake themselves out of it. I seem to recall in Psychology 101 the claim that exercise can help depression, probably by clearing some of the chemicals away. But depressed people are too unmotivated to try it.
So medication should not be used as a cure, but as a way of reducing the overload enough so that they can restore themselves enough to avoid the overload once they get off the medication. This should deal with the majority of cases, except for those where the overload is caused by an actual physical malfunction, and not by simple circumstances.
As for why depression is so common, we might be able to look at the modern lifestyle for the explanation, as opposed to an evolutionary explanation.
I seem to recall in Science blog reading 101 the claim that exercise can help over time, likely because depression repress neuronal cell birth from stem cells while exercise promotes it and thus potentially alleviates symptoms.
Is that the effect you remember, or was it a short term effect?
I think it was more of an immediate effect; some of the depression was alleviated if they did some direct physical exercise.
Then again, I might be confusing that with stress; that class was a couple of years ago.
No, that can be it. Depression is correlated with stress.
Also, I hits me that the model I seem to remember in my comment may be a protective effect, not necessarily a treatment.
This amounts to a form of ‘group selection’, something of which individual genes are incapable of foreseeing.
@barcsb: Depression is pretty much the opposite of problem-solving. This is the thing that jumped out at me in the original argument — a depressed person generally doesn’t take time out to ruminate, and to solve problems; they’re busy being depressed!
Maybe the mistake here is that depression could look like deep thinking — you know, with the solitude and the quiet contemplation thing going on, but that seems such a trivially wrong connection to make that I can’t really believe it.
Jerry, thanks for the article, I found it fascinating. I also think that people who believe in withholding medication because pain is good for you have a really odd approach to medicine.
Sometimes, though, it might be the best thing in that situation, especially with anything mental. Taking away the symptoms of depression or a mental problem might also remove the motivation to FIX the underlying issues, at which point you simply end up with the person being on medication for the rest of their life for a problem that they could actually solve.
Well, like anything, it’s case by case. Medication can also provide room to find motivation.
Clearly, verbosestoic has never actually suffered from real depression.
To put it more clearly — like the authors, you have conflated “clinical depression” with “being sad.” The latter can, indeed, be a quite useful motivator depending upon the circumstances. The former tends to sabotage itself, because even if the underlying issues are purely mental, actual depression (as opposed to sadness or other vague negative feelings) has a tendency to undermine motivation.
It is far more common for sufferers of clinical depression to finally have the motivation to fix underlying issues only after the depression is treated.
That said, the observation that there are often underlying issues which need fixing is one argument to prefer C-B therapy as the primary treatment rather than antidepressants — though as I pointed out in another comment, with most people’s insurance policies, the pills are way way cheaper…
Um, considering that my long post pretty much FLAT-OUT SAID THIS, I find your objections here mostly irritating.
Here, I was merely objecting to the idea raised that seemed to say that if someone even SUGGESTS that not treating such a condition might be beneficial there’s something wrong there. Of course, he clarified that he didn’t really mean that, and I pretty much let it drop.
Again, my main point in the post that dealt with it specifically was that it was probably an overload of existing systems, so you take the medication to get the levels down enough so that the underlying problems can be dealt with. You generally don’t treat the medication as a cure, though.
So, essentially, you are vigorously agreeing with me.
Posted May 27, 2010 at 7:01 am:
This is complete nonsense. Being depressed actually destroys the resources one would otherwise use to solve problems; there is strong and widespread evidence that being depressed harms problem solving ability, and even that this harm can be long term, continuing to affect the individual after the depression is gone. More importantly, there is substantial evidence depression reduces motivation to solve problems.
Yes, yes, yes, said it before, and was just replying to a comment that seemed to be suggesting that even suggesting that suffering through the pain was suspicious medically, which was clarified, thanks for playing.
No, it seems to me he clarified that there is a difference between individual outcomes and the general treatment/non-treatment effect. In the general case it is immoral to suggest that non-treatment is beneficial because of some individual outcomes differ, because the general effect does not support that outcome.
It is analogous to saying that being shot is good for some because those individuals survive and may then take care of not being put in that situation again, move to better neighborhoods et cetera.
In the more specific medical context treatment concerns the individuals health and well-being, not his social problems. There is no reason why a medical treatment would look at such effects, but every reason why it should focus on the health benefits. The “problem solving” idea is a treatment problem, not a potential treatment solution.
The moral and treatment problems are what concerns commenters here, that the suggested scenario is not an outcome of treatment nor non-treatment, not whether individual outcomes are different from the norm.
Actually the later are examples of religious thinking, which seems to be a theme here.
No treatment of depression is a cure. Depression may spontaneously remit, never recur, et cetera, and every treatment for depression increases both the rate and the likelihood of that (to my knowledge).
In that respect every treatment is a potential short term or long term cure.
“examples of religious thinking”, i.e. miracles and other exceptions assumed as being normative, to be clear.
Fascinating hypothesis: “busy bein depressed”? what does it mean?
It means “rhetorical flourish”. The contradiction of depression and being busy is used to highlight the absurdity of the adaptation argument.
For some people (that being emphasized), there can exist a byproduct effect of resilience applicable to identifying and avoiding future states of melancholy or dysfunctional reactions to trauma (not ad hoc problem solving, but a step towards self-awareness). This could result in favorable consequences brought about by cognitive behavior processing that allows for the innervation of neuronal plasticity. In this scenario, depression is clearly not an evolved adaptation but presents an unintended opportunity (for some people) to engage parts of the brain that may result in a positive “side effect” with fitness payoff at a later date. Nonetheless, major depressive disorder would be a roundabout, inconvenient, risky, and very ineffective way of having to get there. I like to think of it as cognitive evolution using trauma as experiential leverage for self-actualization. See Lewis Wolpert’s “Malignant Sadness.”
Jerry, your piece is the most cogent takedown of lazy evo-psych I’ve seen. My background is research psychology, and I worked for many years doing clinical research on depression. I have always found infuriating how vague and handwaving the claims of evolutionary psychology are, especially in the realms of mental disorders. The clear criteria you give for determining adaptation are almost never addressed in the Just-So stories that get told in evo-psych, and it is refreshing to see this problem addressed head-on.
This is a good, thought-provoking article.
Perhaps some of the confusion is missing the difference between an individual “adapting” psychologically to a difficult situation and “adaptation” as it is used by biologists. Before one ventures to write a paper on a biological topic, it seems wise to get the biological terms right first.
Anyway, it’s hard to see how anything other than mild and short-term depression could be a very good “adaptation” even in the first, psychological sense.
Yes, liminality would be the word that comes to mind.
Unfortunately, so much of psychology ends up being a speculative “art” without empirical restraint.
adapting psychologically is an adaptation.
But is it reliably heritable?
I don’t see how A&T can reject EBM, whether or not their biological premise is flawed. Evolution is science based, ergo you would go where the evidence leads you for best treatment.
Whether of not the untreated symptoms are helpful (“solves problems”) is inconsequential. You wouldn’t cultivate debilitating cancer just because inability to work helpfully gives you free time!
I guess I would say that their suggestions are both scientifically and socially flawed.
The flawed biological premise is truly and seriously flawed though. Disregarding their “adaptation” criteria, it is as if they suggest that miscarriage is an adaptation.
But I wonder if that analogy doesn’t stand up for their criteria as well:
– “It is common.” ~ 70 % of fertilizations, IIRC.
– “There is a structure whose absence reduces … .” Remove the fallopian tubes, no fertilizations.
– “… involves a group of “coordinated” symptoms.” Symptoms includes resumption of menstrual cycle and fertility.
Presumably miscarriages for A&T is a method to increase fertility by solving its regulation problems.
It isn’t exactly the same by any measure. But if alcoholism is “decreased sensitivity to alcohol”, the paper on gene-culture evolution that WEIT referenced a while back have the hypothesis that some asian populations _increased sensitivity to alcohol_ is an adaptation – against alcoholism!
you are kiddin’ ?
And perhaps lactose intolerance is an adaptation against having the milkman shag one’s wife whilst at work!!
WHAP WHAP WHAP WHAP WHAP!!!
Ouch. What a spanking.
This is why I love science.
Great article, but I disagree with your point about segregating variation being difficult to maintain in this case. This may be surprising for a trait affected by a single locus, but not one affected by many loci and quantitative inheritance. Depression almost certainly is a complex trait with many genetic loci and many environmental factors that can affect the expression of the trait. I may be misinterpreting, but it seems you are saying that if the optimum phenotype is to be 6’4″ tall, you will find no people who are 6’2″ (at least factoring out environmental effects)? I think we can very well argue that a population may be selected for “tall height” or “slight depression”, and still see substantial variation about those means for complex traits (it’s can be very hard to fix an exact combination of 50-some independently segregating alleles in a population!). The evidence in nature bears this out as well. Genetic variation in quantitative traits is ubiquitous.
The question is why a trait that is supposed to be under directional selection (unless height, which is under stabilizing selection) is genetically variable. They have to deal with that. If it’s mutation-selection balance and depression really isn’t under directional selection, then they have to state it.
That may have been their intention, I haven’t read their paper so I’m cheating off your notes. However, doesn’t strong stabilizing selection exert stronger selection on the genetic variance than strong directional selection? If the optimum for the right amount of depression was very far away from the population mean (strong directional selection), then mutations in any one of the many loci that effect that phenotype would have a fairly high probability of being advantageous and would sweep through the population in successive waves, greatly inflating genetic variance as they do. All this requires is that the population is not mutation limited (and yes, there can be tradeoffs with other traits, but now we’re talking about multivariate optima and multivariate genetic variance). Mutation limitation is very likely for a single locus, but not at all obvious for a trait as complex as depression. I suppose the optimum could be continuously moving, but I don’t see why that would be necessary for their argument to hold. That being said, I think their argument is very poor for all the other reasons you list in the article.
Example: Fitness is one of the most complex traits, and is consistently under strong directional selection, but there is always genetic variation for fitness in a population.
Good article. I suffered from severe depression for many years and, although obviously this is anecdotal, it consisted in a total lack of motivation and a near-delusional inability to even consider practical problems, let alone solve them. Basically the opposite of their suggestion. There’s also decision paralysis. Just choosing what to eat for dinner becomes a difficult task (not that you enjoy it either way). (That said, there was definitely a heightened interest in less practical subjects; philosophy, science, “the meaning of it all,” etc.)
What I find most absurd about their proposal, though, is just the very that social (personal) problems can be “solved” by rumination. That runs counter to both intuition and a lot of research in behavioural psychology. (There are experiments that show going with your initial intuition on such matters leads to a happier outcome.) I’m even tempted to state the opposite: much rumination is really the expression of depression and anxiety, rather than adaptive problem solving. If you spend a lot of time ruminating over a particular decision, it’s probably because you’re anxious about it, rather than vice versa.
Indeed, “repetitive thoughts” are one of the hallmarks of pathological depression. Even if we buy into this (evidence-free) rumination hypothesis, it still ought to be painfully obvious that, in the vast majority of sufferers of clinical depression, the purported “adaptation” has run amok.
I have to say, even if we totally bought into this ARH theory or some other adaptive theory of depression hook-line-and-sinker, it would not at all follow that antidepressants should be avoided because the patient should “endure the pain.” By analogy, there is NO doubt that human fertility is adaptive (in fact I think that’s more or less a tautology), and yet nobody is suggesting that doctors shouldn’t prescribe birth control, so that the patient can “endure the children.”
Oh wait, the Catholic church is. Nevermind. But still, you get my point. That’s just stupid. Whether or not a trait is adaptive is completely unrelated to whether people “ought” to choose to indulge that trait or allow it to proceed in its natural manner unfettered.
I do agree that cognitive-behavioral therapy should be the go-to, but for different reasons. Of course, with most people’s insurance, it’s also way more expensive…
OMG, I haven’t had time to read the article, but I have to say “If depression is adaptive, so they say, then people should be encouraged to suffer through its pain to receive its benefits.” is among the worst attitudes about depression I’ve ever seen. That’s saying a lot. Doesn’t this violate the Hippocratic Oath?
Looking forward to reading and commenting on the article.
Psychiatrists and psychologists do not take the Hippocratic oath – only physicians and surgeons.
Are you SURE? Psychiatrists are physicians–they have an M.D. I thought all M.D.s took that oath.
I thought so, too. Maybe they only take that oath if they practice?
Ah, OK, psychiatrists do take the oath.
An excellent critique. Seems to me that most of the output from evolutionary psych is rather brain-dead.
One thing not mentioned in Jerry’s critique is inclusive fitness. This is understandable, since A&T try propose that “depressive rumination” somehow enhances individual fitness, so debunking their claim only requires debunking their argument from individual fitness.
If there is any basis for depression as an evolutionary adaptation, we must consider it a “mental state” or “emotion” rather than a disorder, and then ask what behaviors that mental state leads to. Then we ask how those behaviors might improve *inclusive* fitness. Clearly depression depresses individual fitness, so to be adaptive, it must enhance the fitness of close kin or others who are likely to carry the same “genes” for depression.
What behaviors does depression lead to? Withdrawal, self-neglect, self-punishment, and in the worst case, suicide. All of these behaviors are forms of self-sacrifice. The impact on the kin-group would be a reduction in the resources consumed by the depressed person thereby increasing resources for everyone else. Such self-sacrificing behavior will improve inclusive fitness only when the self-sacrificing individual is an excessive burden to the kin-group *and* it is highly unlikely for the situation to reverse itself.
As it is inevitable that such situations arose quite often in our ancestry, it makes a great deal of sense that genes for such an emotional state leading to self-sacrificing behavior under appropiate conditions would be successful.
I hypothesize then, that depression was never adaptive for the individual. Rather, genes that cause depression-like behaviors have always been positively selected for reasons of inclusive fitness (kin-selection) in any social species. Like most basic emotions, it goes back to our most distant rodent-like, colony or pack oriented ancestors, or even further back.
Depression is often (I would bet almost universally) concomitant with debilitating disease or injury. It is also associated with guilt, regret, feelings of “worthlessness” and so forth. These facts support my hypothesis, but far from prove it.
With my hypothesis, depression is, by definition, maladaptive for the individual, despite the genes for it being positively selected.
For humans, determining whether we are an “excessive burden” to our kin must involve processing a great deal of complex social information. It is not simply a question of assessing one’s own physical state of injury or disease. Our ancestors would have processed feedback from their kin to determine “am I an excessive burden to those around me?” For the most part, we would have been well-adapted to accurately assess the answer to this question in the setting of a small primitive kin-group. We can readily imagine a severely sick or injured individual, knowing that they are unlikely to recover, refusing to eat, especially when food is scarce, so that the other, healthy members of the group would have more to eat.
But in the modern world we get such confused social messages. The sheer mass of society, coupled with technology, reduces the contribution of any individual to relative insignificance. Mass media presents us will any number of “ideals” against which we can compare ourselves and find ourselves lacking. Our divergent social connections (nuclear family, two (or more) seperate extended families, school, career/employer, political parties, religions, social causes, product brands) lead to conflicting values, priorities, and loyalties, so that we are likely to always feel like we are letting down one or more of these pseudo-tribes to which we have emotionally bonded. Anyone who, by normal variation, is genetically more prone to the emotion of I-am-an-excessive-burden-to-my-kin-group will likely develop pathological depression, despite the fact that our technologically derived abundance means that no one is an excessive burden, as a practical matter. (Consider that we can readily afford to care for even the most debilitated individuals in our society — paraplegics, comatose, etc.) Anyone who can put in even a modicum of work is not a “burden” to society, but we may nonetheless feel that we are by comparison to others and/or to unrealistic ideals.
(1) An evolutionary explanation for depression must lie in inclusive fitness/kin-selection.
(2) Depression, by definition, is maladaptive for the individual (in terms of the individual’s reproductive success). Depression may have been beneficial, under appropriate circumstances, to the kin-group of the depressed individual.
(3) Depression in the modern world is pathological because the radically different social-situation generates social signals which more readily lead to negative self-assessment than was the case within a primitive close-knit family group.
(4) I am under know illusions that the above is anything more than a hypothesis. But I do submit that it is a hypothesis which is consistent with evolutionary theory and addresses the question of successful reproduction of the genes involved. While it would be difficult, but not impossible, to gather relevant field data — perhaps by studying highly social small mammal species (meerkats?). Appropriate mathematical models and computer simulations might be able to bear out the hypothesis.
I think you have something very interesting here, and something like this hypothesis can be found in The Lucifer Principle by Howard Bloom. I haven’t read it (or owned it) for a long time… But I’ve just found a nice exert here concerning this very thing: http://howardbloom.net/lucifer/excerpt2.html
I absolutely agree with you that depression is not an adaptation on the individual level. However, there are several flaws with your hypothesis:
1)”If there is any basis for depression as an evolutionary adaptation, we must consider it a “mental state” or “emotion” rather than a disorder…”
While depression could be described as a “mental state” of a sort, it is most definitely no mere “emotion.”
2)”Withdrawal, self-neglect, self-punishment, and in the worst case, suicide. All of these behaviors are forms of self-sacrifice.”
What about symptoms such as hyperphagia – excessive eating, increased appetite (the opposite of a self-sacrificing behavior), insomnia or hypersomnia, persistent aches or pains, markedly diminished interest or pleasure in all or most activities? (none of these involve self sacrifice that would benefit kin).
3)”Depression is often (I would bet almost universally) concomitant with debilitating disease or injury.”
Not so. Depression frequently exists in the complete absence of any injury or debilitating disease (unless depression itself is the debilitating disease) and not all persons with injuries or debilitating disease become depressed (this *may* be common, but is not universal).
4)” We can readily imagine a severely sick or injured individual, knowing that they are unlikely to recover, refusing to eat, especially when food is scarce, so that the other, healthy members of the group would have more to eat.”
This is not a description of depression and the motivation behind suicide is to end ones individual suffering. It is not self sacrifice for the sake of kin.
5)”…perhaps by studying highly social small mammal species (meerkats?). Appropriate mathematical models and computer simulations might be able to bear out the hypothesis.”
Meerkats, mathematical models and computer simulations to model a complex psychological syndrome such as depression? I can’t imagine such studies would provide any wothwhile information.
“…depression could simply be a maladaptive byproduct of a feature that is generally adaptive—perhaps the wiring of those brains. Viewed in this way, depression could be a “spandrel,” a genetic hitchhiker that is a byproduct of something else.”
Something else like… my syrupy sweet golf swing, or my devil-may-care good looks, maybe? I KNEW there was an explanation for those things!
Seriously though Professor Coyne, that was a marvelous and most erudite piece of science writing, and I think you for the information. Your main point seems crystal clear:
If “depressed people” don’t differentially produce more offspring than “non-depressed people”, then evolutionary psychologists better keep hitting range balls.
Great post. Syncs up well with the class I just took on Behavioral Genetics. Thanks!
To some: please note the difference here between evolutionary psychiatry (where ARH seems to be mostly based) and evolutionary psychology. The latter to me seems to have more potential, at least when it can bare fruit through neuroimaging and cognitive science to bridge the gap between genes and behavior.
That’s not to say it’s never abused (see much of the debate around the “gay gene” or “god gene”)… only that I think there are some actual hardworking empiricists in the psychology field.
A good sign is when start by embracing measures of prevalence through pedigrees, twin or adoption studies, or proper linkage or genome scans… rather than skipping straight to conclusions about behavior like I get the impression Andrews and Thompson were doing.
Can you point me to any study in evolutionary psychology that would meet the standards Jerry sets forth?
Fuck that noise.
If I hadn’t had my meds I wouldn’t have had the wherewithal to gain anything from my therapy.
Is that yet another “nature is perfect and can do no wrong” cult? I think I’ll write a paper on how flat-footedness or clubfoot are adaptive. Then again it may be easier to write a paper about how a cleft palate is adaptive.
Oooh – I’ve got a better one: a perforated interventricular septum is adaptive.
I just saw a Viagara commercial. Erectile dysfunction must be adaptive, or so many people wouldn’t experience it. Right???
Death must be very adaptive then.
Thank you, Prof. Coyne, for pushing back against this idiotic narrative. As a person who has actually suffered from depression, when someone suggests it is “adaptive” because it “helps solve problems” I don’t know whether to laugh or throw something across the room. Depression doesn’t mean you don’t go out dancing and thus have time to think about your life; depression means you don’t do much of anything. Period. It means hours of watching pointless TV or playing Solitaire, if you can bring yourself to get out of bed at all. It is a sapping of mind as well as body, a dearth of hope in better days coming along.
Anyone who says depression is a helpful condition literally has no idea at all what they are talking about.
thank you, i was about to slap them for thinking they could simulate depression by playing ‘sad music’; what garbage. how you described depression is exactly spot on.
rather than an adaptation maybe it was something that just wasn’t bad enough to stop a someone from mating and having kids so it stuck around? some spandrel from the development of something else maybe?
One has to wonder whether the original authors had ever actually dealt with a really depressed person.
At least one of them is a practicing psychiatrist who sees severely depressed patients on a daily basis. I think this is in the NYT article.
That’s disturbing. But not really surprising.
The Scientologists might actually be on to something! 😉
A practicing psychiatrist generally means they meet with a patient for a 20 minute appointment every 3 to 6 months. But still, their attitude about depression and medication is outrageous (caveat, I haven’t confirmed this characterization myself, relying on Jerry). This is whole different topic, but I would think prescribing meds simply as a placebo would be called for in most depressive cases.
Have a look at the New York Times article to which I linked; it talks a bit more about Thomson’s own practice (he’s the psychiatrist). The article says this:
Did he say HOW he statistically tested his various procedure/results ratios?
Or is it all going on ‘feel’?
“…he says, he now believes that the drugs can sometimes interfere with genuine recovery, making it harder for people to resolve their social dilemmas.”
And he’s basing this on, as has been amply demonstrated by Jerry and others, a ridiculous evo-psych hypothesis. As is unfortunately the case with many in the mental health profession, this man could likely be doing more harm than good.
Just to point out that a high mutation rate can also maintain genetic variation. The alleles associated with Huntington Disease persist at high frequency despite being both dominant and deleterious to reproductive success. They just keep cropping up. Doubtless nothing to do with depression.
Anyone who says depression is a helpful condition literally has no idea at all what they are talking about.
“A subdiscipline, evolutionary psychiatry, tries to find evolutionary explanations for mental disorders”
This line bugged me; it gets the definition as wrong as Andrews and Thomson were about using ‘adaptation’.
I think it’s more about looking at the problem of how the mind works, from language and memory to how the mind processes stereo vision and creates a perception of the world in the mind, and using evolutionary biology to try and find how and why the mind is set up the way it is to be able to develop.
I can see how some psychologists may use the term ‘adaptation’ a little loosely, but psychology has never been more grounded in reality since the problem has been viewed from an evolutionary perspective (see Steven Pinker, Gary Marcus, Stanislas Dehaene, Christine Kenneally, etc.) There are some who take it too far, outside the realm of the testable, but it is nonetheless a fruitful field.
Biology isn’t without its proponents of just-so adaptation stories, so why harp on a whole field because it to has its share of just-so adaptionists.
As a layman I’m trying to wrap my mind around how evolutionary psychology has an “evolutionary perspective” and is “using evolutionary biology” if it isn’t viewing human behaviors as “products of natural selection that acted on the psychological traits of our ancestors”.
That is, aside from the problem that if it is merely “using evolutionary biology” as a method among others but is actually psychology at large, the whole field is a misnomer.
[And yes, I have read some basic text of Pinker, but I can’t remember the methodology as laid out in Coyne’s post or in the gene-culture review I just read. Also, the feeling I got that it looked at using evolutionary biology as a research strategy, not a methodology.]
regardless it was just the definition that bugged me; whether for methodological or strategical purposes (i’m also a layperson fyi), the goals were laid out here as only looking for “evolutionary explanations for mental *disorders*” seems off, the disorders are of the least focus, if any.
from what i’ve read it’s more about trying to figure out what a certain mental feature was originally meant for, like why we like sex for instance. we like sex because liking sex lead to having more babies, so it was a psychological trait that stuck around. i don’t think that’s terribly controversial and it would be considered ‘evolutionary psychology’, no?
anyway, i just felt that the whole field of evolutionary psychology was being bashed becuase there are people who like to weave just-so stories, when regular biology has just-so stories too, so it would be odd to poo-poo the whole field because of some sloppy thinkers.
oh wait, i saw the error, my fault, i read psychology and psychiatry as the same….
thought it was an odd paragraph…
must be dyslexic :/
yes ignore everything i posted….
You conflate psychiatry with psychology here.
i actually read both as psychology, hence the dyslexia comment. it wasn’t until the fourth or fifth time i read it that i saw my error. totally my fault for reading too fast
Sorry Ken, meant to reply to the article, not to your comment.
Thank you for writing this. Maybe for some depression is linked to a clear cause that needs to be worked through, but not so for me. My life was (and is again) fantastic, yet I was hit by severe depression. I could not even muster the energy to feed myself or shower. Thankfully, I got medical intervention. Talk at that stage would have been reckless and futile.
I can see where depression is not an adaption for survival but one should not forget that another mental disorder can confer considerable positive survival advantages. Bipolar disorder when the sufferer is in a hypomania early-to mid-mania period can give considerable evolutionary advantages such as a very high libido along with an amazing ability to charm and to seduce. Add that to an extraordinary focus in work, creativeness, hunting or story-telling and you definitely find a good reason for Bipolar disorder to be survival-enhancing.
There are two poles to bipolar disorder. The other is depression. What’s the overall effect on reproduction?
And if psychiatrists want to see this as an adaptation, they should measure the reproductive output of bipolar people before they start making up stories.
And THEN, if they find a reproductive bonus to bipolar disorder, they have to explain why everyone isn’t bipolar.
Suffering from depression myself I have a bit of a bias, and I generally agree with evo-psych concerning mate selection and sexual behavior but I don’t think depression has any adaptive value. My pet hypothesis is that there are high levels of depression in developed countries for reasons similar to the reasons there are high levels of obesity in developed countries. It’s a byproduct of living in a society vastly different than the one we evolved in. I don’t really have any mechanism to explain how this might work but, I think the byproduct theory is more likely than the adaptive theory.
I’m an evolutionary psychologist with an interest in individual differences. I’m not here to defend the rumination hypothesis, which I don’t find persuasive. I also agree (as I believe most of my colleagues do) that major depression itself is probably not an adaptation but a pathological byproduct. However, I wish to respond to the argument that people should “count babies” everytime they propose an adaptive hypothesis. This is incorrect for two reasons:
1) Mass contraception has recently broken (or at least severely muted) the link between mating behavior and reproductive success in modern societies. This is an unprecedented event in human evolution, and it would be foolish to act as if it didn’t happen. In fact, it would be much easier for evolutionary psychologists to just go on and count people’s offspring – the problem is, it doesn’t work well. This is why we resort to proxies such as status, number of partners, investment in childrearing, and so on (by the way, biologists do this quite often as well, for example when they use offspring weight as a proxy of their reproductive potential). Take social status as an example. The relationship between status and reproductive output in modern societies is weak and inconsistent. Certainly, it can tricky to show that it -would- increase reproductive success in modern societies weren’t it for the intervening effect of contraception. But it can be done, and indeed has been done by Perusse (1993): Cultural and reproductive success in industrial societies: Testing the relationship at the proximate and ultimate levels. Behavioral and Brain Sciences, 16, 267-322. In addition, there is a lot of work in traditional societies (no contraception) in which evolutionary antropologists do count babies, and consistently find positive relationships between status and number of children. Taken together, these findings allow one to use social status as a proxy for reproductive success in past environments, without any post-hoc storytelling involved. That said, many traits that were adaptive in the past may still be adaptive today – but this is an empirical question. For example, there are data indicating ongoing positive selection on wealth accumulation in human males. Nettle & Pollet (2008): Natural selection on male wealth in humans. The American Naturalist, 172, 658-666.
2) The lifetime reproductive output of a single individual carrying a certain allele is not without problems as a measure of fitness. Examples: (A) The environment may fluctuate cyclically, with different genotypes being more successful in different phases of the cycle (e.g., resource scarcity versus plentiness). This mechanism has been shown to maintain genetic variation for personality traits in birds, and may be relevant to humans as well. (B) some reproductive strategies may lead individuals to invest more heavily in fewer offspring, with positive effects on long-term fitness at the cost of reduced reproductive output in the present. For this reason, the strategy (or allele) that produces more offspring in the short term (i.e., a single generation) is not necessarily the one that wins out in the long term (i.e., multiple generations). See e.g., Houston & Mcnamara (1999): Models of adaptive behaviour. Cambridge. (C) there may be sexually antagonistic effects, so that an allele has (say) positive effects in females but negative effects in males. In such cases, counting children without a good theoretical model would result in a null.
3) There are several other ways to gather evidence for or against an adaptative hypothesis, and they are employed in biology as well. They include mathematical modelling, experimental analysis of proximate function, cross-species comparisons, and so on. Not every biological study of adaptation goes on to directly measure reproductive success.
Finally, alternative hypotheses such as those suggested in the post have already been put forth by evolutionary psychologists: For example, Daniel Nettle’s work on schizotypy is based on the hypothesis that schizotypy (a suite of traits that increase the risk of psychosis) is advantageous, but psychosis itself is not. He also showed that schizotypy in healthy individuals predicts mating success, a proxy of actual reproductive success in past environments: Moreover, Nettle & Clegg (2006): Schizotypy, creativity and mating success in humans. Proc. R. Soc. Lond. B 273, 611-615. To the question “why aren’t we all schizotypal then”, there are at least two plausible answers: (1) stabilizing selection against the extremes of schizotypy, and (2) the fact that schizotypy increases mating success only with short-term partners; the (documented) presence of alternative mating strategies in humans would make schizotypy adaptive only for a subset of the population, i.e, those engaging in short-term-oriented mating strategies.
It seems to me that the argument has moved on a little. Firstly there is and never has been any evidence that clinical depression is caused by genetics, “faulty genes”, and even artificially lowering serotonin levels doesn’t produce depression see: ‘The antidepressants dirty little secret’http://www.uncommonhelp.me/articles/antidepressants-dirty-little-secret/
I suspect depression is adaptive in the sense that hunger is adaptive when you don’t eat and thirst is an adaptive signal when you aren’t getting the hydration you need. When people move from living in traditional (what some people call “primitive” societies) to westernized ones they instantly the adaptive response to living in such a culture is a much greater vulnerability to clinical depression. So what might depression adaptively signalling us?
Depression is much rifer in industrialized or “westernized” cultures in which basic emotional needs of individuals are not met as an easy and natural by-product of the way the culture is constructed.
Basic needs for quality attention giving and receiving, a sense of community, a sense of purpose, a sense of connection to something bigger than oneself, clear secure life/work roles and status, a sense of control and autonomy over ones life, a natural relationship to physical exercise and rest, and so on are less likely to be easily met it seems in modern cultures (in which rates of depression have sky rocketed over the last fifty years).
We all have innate drives to meet needs that help us flourish as individuals and societies. Depression would be needed to signal to both the depressed person and people around him or her that needs are not being met. By unfairly labelling the depressed person as “diseased” or genetically handicapped we are acting like the person who when confronted by the agony of a starving man assumes his current suffering is caused by his unfortunate biochemistry.
If we can all agree that all human beings share recognizable emotional and physical needs (which makes us recognizably human) then we could also agree that there would need to be a recognizable “signalling system” within a person that activates when basic emotional needs are not met for any length of time just as when thirst or hunger of physical pain is activated when needs for food, water or physical safety are not being met.
If the “pain” of depression isn’t a signal that the structure of ones life is damaged and required emotional needs aren’t being met I don’t know what is.
People can, of course, become depressed even when all seems to be well in their life but if someone habitually uses depressive attribution styles” when reflecting about themselves and life’s events then this “perceptual bias” in itself will be blocking the sense of their emotional needs being properly met and therefore still be producing the pain signal that is clinical depression. Attitudes and “memes” are highly infectious people can learn to be depressed from others in their lives. Fortunately when we are clear about basic needs and how people construct their personal realities then we can actually start to help people.
Suppose that, instead of an individual trait, depression is a societal trait that selects out groups who are less able to perform within society taken as a super-organism?
I have been taught (at a highly esteemed research institution, Penn State, by one of my psychology professors) that depression is a signal to those people surrounding the depressed person that something is wrong. The symptoms elicit help from the family/kin group. As in, ‘hey I feel pretty damn worthless, what is the point of life?! and I have been contemplating killing myself” — People can’t usually ruminate on these things for extended periods of time without family members knowing, or feeling that something is wrong. Depressive symptoms are a cry for help, “Remind me why life is good, help me through this”…. It can be adaptive for the individual in that they do not end their own life and actually reproduce, getting their genes into the next generation, and increasing fitness.
As for suffering through depression, whoever suggested that clearly never suffered from it firsthand.
It can also be argued endlessly whether depression is a more ‘accurate’ view of the state of affairs of ones life. Yes, everyone does die, so what is the point in continuing to get up everyday? (Obviously there is a point – the thing I finally fixated on and got me out of bed was love) Is everyone who is not depressed just succumbing to illusions – adaptive illusions that increase fitness?
Well, if your esteemed psychology professors taught you that this is even a semi-established fact, you’re not being well served. If they didn’t give any evidence that depression evolved as a signal, then they’re just talking out of their nether orifices. I suppose you could claim that groaning when you’re sick is a sign to others that you’re not well, too!
This discussion is interesting. For me, and I do suffer from depression, depression is part of my artistic personality. Depression, as a kind of suffering, makes me grow spiritually and intellectually. There is a correlation between genius and madness. Also those who suffer from depression, statistics show, are more inclined to see reality while most people live in the delusion that everything will be OK. People, as statistics show, tend to be over optimistic. Depression makes people more aware of the problems. For many artist great art work comes from depression. As far as evolution depression, like other mental disorders, could well be an evolutionary mechanism which keeps people more “aware” about the problems we face such as the fact that we are destroying our world and that the clock is ticking. Will we make it in time? Will our children have the same kind of life that we enjoy today? will they be able to live a decent life? These are the pressing questions that are often present in the mind of those with depression. Naturally there are exception and not all people with depression are artistic or worry about the future but I feel that the purpose of depression may be clear in the big scheme of things. It has most definitely a purpose. For me personally it is part of my creativity and the reason why I care for many people and help many via email exchanges. It is also the reason why I develop artistically and spiritually. And yes, over the years, I have learned to control depression so that it does not stop me from living. I have learned to cope with it so that it does not prevent me from doing the things I love. But it takes great commitment, practice, will and strength. I control my depression today, depression does not control me.
Depression, stress and other anxiety-related disorders are a *failure to adapt* to the requirements of modern society. For some people genetics is the major contributor, while for others it’s more about the environment. In a sense genetics is a common factor because the human brain is fragile.
Very belatedly (on this site), I want to thank Jerry Coyne for his superb
article in Psychiatric Times (I am Editor in Chief Emeritus, and invited the piece); and also would like to apprise readers of a follow-up piece I did for Psychiatric Times, available after a free registration step at this link:
Best regards, Ron Pies MD
Is myopia an adaptation??
My thinking is that depression is like myopia. There is a certain amount an individual can have before it becomes a complete blocker of reproduction, even still a blind person is fully capable of reproduction, but it becomes unlikely. Any amount of depression may have a negative affect, however, there are many positive traits that can make up for the depression. Also there seems to be a great variation of the amount of depression one can experience…its not something like blue eyes vs brown eyes….Which also probably has a gradualness to it…Consider this: A person that can get by with having sub par vision (before the advent of vision aids) by having traits that increase their fitness. Of course, an individual with the fitness increasing traits along with ‘perfect’ (no human will have eagle eyes…something also to consider) eyesight is better off, but does not mean the person with bad eyes is completely unfit. Bad eyesight combined with many other fitness decreasing traits may decrease fitness to the point that reproduction is not possible. The same may be said for depression: Depression seems to be viewed as always negative, but if other factors are strong, say intelligence/cleverness/resourcefulness…to the point where the individual with depression doesn’t even have to try to do things better than the others around them, and downplays the ability (I think that would be seen as a positive trait), the chances of reproduction increase (boasting about your accomplishments, overconfidence, and extravagance (the opposite of depression), in certain environments may be detrimental, as we are all human, we make mistakes, the boastful person will loose a lot of trust when they do make a mistake) There could also be certain traits that build well with a certain amount of depression that increase fitness. Basically, I believe that any trait will exist in a population if it doesn’t completely destroy chances of reproduction. Depression, I believe, is one of these traits. I think evolutionarily it should be viewed as not what makes us fitter, but what are we allowed to get away with. Too much of a good thing can be detrimental as well. Depression seems to be something that ideally is kept in balance. Negative thoughts are needed in order to make things better-if not we would all be complacent with throwing our poop at others as a means of communication, sleeping without shelter, not using tools. Progression starts with a negative thought. If things weren’t looked at as being not good enough, nothing would change. These negative thoughts can be overwhelming to the point where they’re turned on the thinker-depression. Now that I think of it, humanity is depressing in that things are never good enough, we always need more money, property, convenience, ‘cool’ stuff…it never ends. The thoughts that drive this progress I think are linked to depression in that they are negative. Where they are aimed is the difference. Very interesting subject.