A friend sent me this New York Times story called Depression’s Upside and my reply email ended up getting long enough I thought I’d blog it. The primary academic source is this interesting article in Psychological Review which also got coverage in Newsweek last year.
The superficial summary is that depression is an evolutionary adaptation, and that is still helping us solve problems in modern society. Is this true? These are two very distinct claims and while each may have some merit, saying it like that may obscure as much as it enlightens. These are not completely novel ideas, and the authors of the original article, Andrews and Thomson, discuss an enormous amount of relevant research. I learned a great deal reading it but I was troubled that they downplay the distinction between low and high levels of depression. Andrews and Thomson justify this in the following paragraph:
It is not uncommon to see arguments that depression might be adaptive at low levels but is maladaptive at levels that reach DSM criteria (Dobson & Pusch, 1995; P. Gilbert & Allan, 1998; L. Lee, Harkness, Sabbagh, & Jacobson, 2005; Markman & Miller, 2006; Nettle, 2004; Price et al., 1994; Wolpert, 2008). These arguments implicitly assume that clinical and subclinical episodes are qualitatively different. (624)
But that isn’t really true in any meaningful sense. Yes, major depressive disorder appears to be the tail end of a continuous distribution of symptoms that we all experience. (Does this remind you of my discussion of social class?) But this does not invalidate other scholars claims that depressive symptoms may be adaptive at low levels and maladaptive at high levels. To be more precise, it is not depressive symptoms which might be adaptive, but the predisposition to depressive symptoms when faced with particular circumstances. They go on to say:
Because we think that the clinical significance criterion leads to the overdiagnosis of depressive disorder, we intend our arguments to apply to a range of depressive symptoms, from transient sadness to much of what would currently satisfy DSM–IV–TR criteria for major depression. (624)
Clinical depression may be diagnosed, but that is not a logical justification for assuming the whole range of symptoms can be lumped together when addressing various issues, e.g. whether depressive symptoms have adaptive value. There is no doubt in my mind that our brains social and emotional processing systems were shaped by natural selection. There is a sense in which our predisposition to react to particular situations with depressive symptoms must have been an adaptation. But severe depression is obviously not an adaptation. Adaptations increase inclusive fitness; severe depression does not. Frankly, I think Andrews and Thomson are negligent in not pointing this out. In failing to discuss it, they lend sympathy and comfort to those who would argue that even severe depression is a morally or medically necessary state that people need to “earn” their way out of.
Another idea Andrews and Thomson spill too little ink on, is that severe depression could be the result of a mismatch between the environment our brains evolved for, and the modern environment we have created. This is the same logic behind why we instinctively eat more fat and sugar than is good for us. One of the ways to test this is to estimate the prevalence of severe depression among hunter-gatherers. Though at least one scholar (Ness) has argued it is far lower, but my googling wasn’t able to find strong evidence for or against this claim. I can recommend another review article which focuses on the broader issue of how mental disorders could have evolved.
When I was reading all this I identified a few questions I thought might clarify the issues:
Do people on a semi or fully unconscious level choose depression because it helps them achieve certain goals?
Well, if its an unconscious decision, then in a sense, evolution chose it… a huge amount of our behavior is best understood as unconscious, but the word choice is probably misleading in this circumstance. I think it is usefully descriptive to say that some people semi-consciously choose depression, but that is only because their other options appear (to them) even worse, e.g. giving up deeply held values.
Accepting that depression can on some level be understood as assisting in the achievement of certain goals. To what extent are those goals aligned with maximizing inclusive genetic fitness?
Very little for most people in modern society, perhaps (speculation) more in the environment of evolutionary adaptedness.
How should an individual or society weigh the goals depression helps achieve and other alternative goals, e.g. not being depressed?
I don’t have a good answer for this and would be skeptical of anyone who was highly confident of their own answer. That said, I think it is fair to say that most cases of depression have little redeeming value. So it seems reasonable to want to reduce depression and to be willing to consider pharmaceutical approaches. On the other hand, their track record is extremely spotty. I know that some researchers have claimed that physical exercise and some forms of therapy are as effective as drugs. I expect that fifty years from now we will look back on how we’re treating depression and conclude that we were doing it wrong (not that we will have discovered the perfect treatment). But that’s life, we have to make choices today with our very incomplete understanding of the world.
One final note, I noticed I found myself writing about “depressive symptoms,” rather than “depression.” Psychiatric diagnoses, including depression, are not particularly well defined. On the one hand, we all use the term depression because it communicates something, on the other hand it conceals a lot of complexity that psychiatrists don’t understand very well… it would often be helpful if researchers would focus on something more fine-grained, i.e. clusters of symptoms.
Andrews, P., & Thomson, J. (2009). The bright side of being blue: Depression as an adaptation for analyzing complex problems. Psychological Review, 116 (3), 620-654 DOI: 10.1037/a0016242