Evolutionary Theories of Depression: A Critical Review

Abstract

We critically review evolutionary theories of major depressive disorder (MDD). Because most instances of MDD appear to be caused by adversity, evolutionary theories of MDD generally propose that sadness and low mood evolved as beneficial responses to adversity, and that MDD is dysfunctional sadness and low mood. If so, MDD research should focus much more heavily on understanding the healthy functions of sadness and low mood to better understand how they dysfunction. A debate about the boundary between healthy sadness and MDD is then reviewed. In part, this debate turns on whether MDD's costliest symptoms could provide unknown benefits. Therefore, the review concludes by discussing 2 theories that explore possible benefits of prolonged anhedonia and suicidality.Can J Psychiatry. 2011;56(12):716-726. Clinical Implications• The clinical implications depend on which, if any, of these evolutionary theories of MDD is correct. In general, if MDD is dysfunctional sadness or low mood, then the primary goal of psycho-or chemotherapy would be to restore healthy sadness and low mood, and not simply to reduce MDD symptoms. Conversely, if MDD is functional, then therapy would aim to solve the social problem that triggered the MDD.• In particular, if MDD is an involuntary subordinate strategy, then therapy should involve encouraging patients to let go of important but seemingly unobtainable life goals that involve conflicts with higher-status people. However, if the analytical rumination hypothesis is correct, then therapy should instead focus on identifying and solving the complex life problem that triggered the MDD. In some patients, and contrary to the involuntary subordinate strategy hypothesis, this may involve redoubling efforts to achieve a seemingly unobtainable life goal.• Finally, all psychosocial theories of MDD imply that it may be possible to prevent MDD by identifying and avoiding social risk factors. For instance, the credible signalling hypothesis highlights the potent MDD risk posed by the confluence of social conflict, powerlessness, and adversity, each of which, in principle, could be reduced with appropriate interventions. Limitation• The primary limitation of all evolutionary theories of MDD is that, although each is a reasonably parsimonious account of known facts about MDD, few of their novel predictions have been explored. In other words, these theories are largely untested.

The Signaling Theory of Symptoms

“…Sharing a similar basis, the ''social navigation hypothesis'' (Watson & Andrews, 2002) and the ''bargaining model of depression'' (Hagen, 1999(Hagen, , 2002(Hagen, , 2003(Hagen, , 2011; see also Rosenstrom, 2013) explain selfharming behavior in depression from drug abuse to suicide attempts. In interdependent relationships, like the family or a foraging group, harming oneself also imposes costs on others: Other people who usually depend on or cooperate with the depressed individual are left to their own devices when the self-harmer is injured or dead.…”

The 52 different symptoms of major depression: lack of content overlap among seven common depression scales

“…MDD has been understood, among many others, as a brain disease, a clinical form of grief, an adaptive response to recurrent fitness threats, a set of self-defeating attitudes, and a strategy to conserve resources (Hagen, 2011;Santor et al, 2006;Snaith, 1993). The BDI symptoms, for instance, are based on the particular concept Beck and colleagues had about depression, and the scale features many cognitive symptoms that were central to Beck's theory (Beck et al, 1979).…”

Why Has Natural Selection Left Us So Vulnerable to Anxiety and Mood Disorders?

“…Dr Hagen is correct that we should, like other physicians, investigate what may be arousing symptoms before jumping to the conclusion that they come from abnormal mechanisms. 2 Some have argued that medication treatment for mental disorders is justified because they are caused by brain abnormalities. This unnecessarily limits the use of treatments in psychiatry that can, as in the rest of medicine, relieve enormous suffering by blocking normal aversive responses that may not be necessary for this individual in the current situation.…”

“…2 Much of what general medicine does is to use medications to block normal defensive responses, such as pain, cough, and fever. We can do this safely most of the time because the body has redundant defences that are regulated by mechanisms shaped according to the smoke detector principle.…”

“…Evolutionary medicine suggests that this is only 1 of 6 reasons why selection has left us vulnerable to diseases. 4,5 Two others, emphasized in these articles, 1,2 are that some conditions that seem like diseases are actually defences, and that every trait is subject to trade-offs; making it better in one respect will make it worse in others. When I first did this calculation, I could hardly believe it.…”